4 a four for wireless a azme

4

A FINE FOUR FOR /5

Wirelessa azme

EDITOR: BERNARD EJON ES TECHNICAL EDITOR J. H.REYN ER,B.sc(y0,04.m.tEE:

:VOL 8. N°43. AUGUST 928TH JIM'

Civcr " A 0: (:)

(j)IL f

OAP

40,

BLUE PRINTS of THIS MONTH'S SETS AT HALF PRICE

Wireless Magazine. August. 1928

READY?AYE-EVER READY!

For loyal, unflinching Service

BRITAI NS BEST BATTERIES

Wireless Magazine. August. 1928 ...... Volume VII

No. 43

1111

Wireless Magazine"The Best Shillingsworth in Radio "

PAGE

CONTENTSPAGE

The Five -pounder Four. Toy Balloons and X -Rays .. 37Receives Over Twenty Stations " Different " Crystal Circuits .. 37on the Loud -speaker .. 5 Half Hours with the Professor.

Under My Aerial. Halyard's A Chat About Screened -gridChat on the Month's Topics.. 10 Valves .. . . 38

Some " Home" Additions tothe Chummy Four.. .. 13

Mixed Grill .. ..Intervalve Couplings for Your

Portable. By Capt. H. J.

40

Seeing Distortion .. 16 Round, M.I.E.E. 41

Summertime D.X. Work ! .. 17 An Efficient Frame Aerial .. 43The Connoisseur's Six. The Are You a Valve Buster? By

Last Word in Super Receivers 20 R. W. Hallows 44bow.

.........August, 1928

Price 1/.

PAGE

The Glee -singer Three. AGramo-Radio Receiver .. 55

Doubling the Number of LicenceHolders ! By B.B.C. Officials 59

The Value of Four -volt Valves.By D. Sisson Relph 61

The Sunshine Five in the NorthCountry. By J. H. Reyner,B.Sc., A.M. I .E.E. . . . . 62

Broadcast Music of the Month.Reviewed by Studius 64

A Moving -coil Loud -speaker .. 681111.

JUST A COMMENT ORIAM not inclined to the belief that we are nearing the end

of the very best "portable" season we have yet had-asentence which has, I fear, two meanings. Undoubtedly

the best portables in the history of wireless have been intro-duced to the public during this summer (and we are proud tothink that J. H. Reyner's Sunshine Five and our Construc-tional Staff's Chummy Four hold premier positions amongthem), but what I have in mind is that the season itself is notending; the vogue of the portable has arrived, and a briefsummer season will not see the end of it.

Perhaps the set of the winter will be a large portable-atransportable-that we can remove at a moment's notice fromthe cold drawing -room to our warm "den" or to the cheeryliving -room without trouble and without sacrificing quality.

As you look through our pages this month you will certainlyescape any suggestion that the portable is waning as the daysdraw in. J. H. Reyner talks of experiences with his SunshineFive in the North country ; Capt. Round offers a helping handto those who would like to design their own portable sets ; wedescrib.e at length the Pilgrim Portable, a headphone set forthe tourist ; and we take the Chummy Four and make it a"home" set by adding a jack for phones or external loud-speaker, and by adapting it for external H.T. supply, etc.

TWO BY THE EDITORBoth,'. H. Reyner and R. W. Hallows speak enthusiastically

this month on summer -time reception.In our "Gramo-Radio Section" Capt. H. T. Barnett

writes upon a most absorbing subject-the angle and theweight of the pick-up. When you are using expensive recordsyou need to see, not only from the point of view of quality ofreproduction but from that of expense also, that the needle isused at the correct angle and that some counter -balance isused to take up the dead weight of the pick-up.

We have a small gramo-radio set, by the way, in this issue,The Glee -singer Three, comprising a detector and two resis-tance -coupled low -frequency stages. The Connoisseur's Six,another fine set in our pages this month, can also be used forgramo-radio work.

One of the most popular features of our issue will be theFive -pounder Four, carefully designed for economical building.In the blueprint of this set (available at half-price to everyonewho sends us the Special Blueprint Coupon during its currency)you will find the shape and full size of every wire used inassembling the set, a system which many novices prefer.

Well, the great annual holiday is upon us, but how quicklyit will pass ! In my next issue I shall be talking about theprogramme for the winter. B. E. J.

How Wireless Helped to Win theWar. By H. de A. Donisthorpe

Valve Soot : What It IsLa Politesse !What Simple Meters Can Show

You ..

25

27

27

28

Continental Studios 30

Successful Short-wave Recep-tion. By J. H. Reyner, B.Sc.,A.M.I.E.E. 31

Broadcasting Organs andOrganestras " .. 33

Valve -leg Spacing 33

To a Fickle Jade. Verse .. 33

The Pilgrim Portable. ATwo-valver for Headphones 34

That Interfering "Verse ..

Radio Music Revivals ..What Readers Think of Our

Sets ..

4545

46

Gramo-Radio Section" Starting Off " . . . . 47" Faking " the Curve.. . . 47Pick-up Angle and Weight :

Are Yours Correct? ByH. T. Barnett, M.I.E.E. . . 48

Lissen Portable Gramophones 50An Outline of Gramophone

Developments . . . . 51

Continental Notes. By Jay Coote 53The World's Broadcasting . . 54

Chinese Telegrams in Morse .. 68The Chummy Four Accumu-

lators .. .. 68W.M." Tests of New Appa-ratus .. .. 70

Comments on the Five -pounderFour. By J. Godchaux Abra-hams ..

A Show(room) Worth Seeing .. 73

Taking the " Ire - Out of Wire-less. By John Simple.. .. 74

The Same Old Songs .. 76Modified H.F. Coupling Unit.. 77Reference Sheets .. 78Useful Accumulator Connector 80The Gramo-Radio Four 80Index to Advertisers .. 80

Published by BERNARD ,ONES PUBLICATIONS, LTD., publishers of "Wireless Magazine" and `Amateur Wireless." Editor : Bernard E. Jones.Technical Editor : J. H. Reyner. B.Sc. (Hons.), A.M.I.E.E. Editorial and Advertisement Offices : 58/61 Fetter Lane, London, E.C.4. Telephone :

City 3733., 3734. Telegrams : "Beejapee, Fleet, London." Published about the 25th day of the month and bears the date of the month following.Subscription : Great Britain and Abroad, t 5s. 6d. a year, post free (Canada only, 135. 6d.). Contributions are invited and will be promptly considered.14 ....10110111

1

Wireless Magazine, August. 1928

1/3

Fit your Valves with66 Balloon Tyres "!

An Anti-microphonic Valve Holder is to a valvewhat the springs and tyres are to a car. Continuingthis analogy the new Ashley Anti-microphonicValve Holder is the " Balloon tyre " of valveholders. It is the latest counter to vibration andits consequences, tending to preserve the life ofany valve and to enhance the transmission to theLoudspeaker.

Special Note to Constructorsof Portable Sets.

The Ashley is the neatest of the superiortypes of Anti-microphonic Valve Holder,it weighs lightly, and permits of 5 valvesbeing placed where normally only 4 wouldfit, of considerable importance to YOU.

1/3

We want you to have a copy of our latest illustrated Brochure,oblige us by completing and posting this slip.

Send Booklet to : -

NAMEADDRESS

ASHLEY WIRELESS TELEPHONE CO. (1925) LTD.,Finch Place, London Road Liverpool:

GET ACOPY

TO -DAY !

NOBODYWho Wants toGet the Best

Results fromThese New

Valves

CANAFFORDTO MISS

THISBOOK

2/6From All Nt.osagents and

Booksellers

Published jointly byBernard .1 ones Publications, Ltd. and Cassell & Co., Ltd.

2

KEEP inTOUCH

Keep in touch with thelatest developments inRadio Science and Prac-tice by buying AmateurWireless every week.In its bright and inter-esting pages you willfind all that is best andlatest in Wireless, writ-ten with understandinga n d authority, a n dcopiously illustrated.Each week sees somenew development inthis most absorbing ofhobbies; some new setto bring yet morethrills to the enthusiasticamateur ; some nattygadget or novel refine-ment.This Autumn will seegreat changes in wirelessdesign. New valves,improved components,new ideas, will set newstandards in Receiverdesign and performance.Keep in touch with thesenew developments

by reading

Every D. EveryThursday Thursday

SPECIALOFFEREBONITEPARTS

L.Described in "Wireless

OF

1928FIVE

Magazine"

.,,,....a,

Jan., 1928

,

LARGE SALES ,,

.

Write for particulars III

to the Sole Makers

THE BRITISH EBONITECO.. LTD. ---L.

HANWELL, LONDON, W.7. '''-----"

,,:

1-1

MID


PolarAll - Wave

H.F. Coupler(2- stage) 250-2,000 metres

IN polished, moulded case suitablefor fitting antiphonic valveholders.

Recommended for the

Sunshine Fiveas explained on page 77

Manufactured Only by

WINGROVE & ROGERS, LTD188/189, STRAND - - LONDON, W.C.2

V.1

Every tender note that the Harpist V ,strikes is faithfully yours, just as Ifshe were playing to you alone as yousit listening -in.

To fully realise the thrill of real Radioinstal Clarke's Atlas Battery Eliminator,which requires No Valves, No Liquids,No Replacements. It gives you indefinitelife and is absolutely foolproof.

The A .C.56 Model (illustrated on right) incorporateshe Westinghouse Metal Rectifier. Retails at £8 15 0including royalty.

H. CLARKE & CO., (M/CR) LTD.Atlas Works, Old Trafford

MANCHESTER

1111011111111i1sui1111111111111111 1111111111111111111111111111111 111.11111111111 111111111111

Ask us to send you folderNo. 31, it is free by post

ive outAliA5

BATTERYELIMINATOR

...

For Alternating CurrentModel 56

11111111111111111111111111111111111111111111111$111111111111111111111111111111111111

:3

1111111111111111111111111111111111iiiiiiliii111111h 111111111111 11111111111111111111111111


Come on and Dance-TO LISSEN'S NEW

PORTABLE GRAMOPHONELISSEN has entered the gramophone trade-with a determinationto make good in it. The first productions are two portablegramophones in different price fields. These are LISSEN 'Sfirst contributions to the gramophone buying public.LISSEN has got to make good in gramophones right fromthe very beginning, and you can be sure, therefore, thatthere is fine value for money concentrated in the two port-able models illustrated on this page.TAKE A LISSENOLA PORTABLE WITH YOU ON YOUR HOLIDAYSDo this year what you may never have done before-take a portable gramophone withyou on your holidays, and be sure it is a new LISSENOLA portable. On the river, in thecar, in your garden, use it indoors. You can take the LISSENOLA Portable Gramophonewith you everywhere. The large model is better than many indoor table grands sold atdouble the price.

The LISSENOLA Portable will happily pass away many of your leisure hours, nomatter where they may be spent. The range of tone reproduction is wider in theLISSENOLA than in many other portables sold at double the prices, because the hornin each LISSENOLA is longer than any portable horn except the most expensivekind. There is a fine sound -box fitted to each LISSENOLA model. The motoris strongly made and silent running. Fittings are bolted on - not merelyscrewed in. They, therefore, do not come loose. Heavilynickel -plated fittings throughout. Case is covered inblack morocco grain leather cloth. Every LISSENOLAPortable is compact, easy to carry, tight, handsomely L I S S E N O LAfinished. The lid of each machine carries eight 10 -inchrecords. Each machine plays up to 12 -inch records. MODEL No. I.

Should your music dealer be unable to give you prompt (Thorens motor)delivery, ORDER AT ONCE DIRECT FROM FACTORY.Kindly give dealer's name and address. State machine 12i" x 101" x 6"required. Remittance may be sent with order, or the £2 : 2 :machine will be sent by return C.O.D. merely on receipt of 0your order on a post card.

7 DAYS' APPROVALIf you are not entirely satisfied with yourLISSENOLA Portable Gramophone after trial,you can return it to the factory within 7 days ofpurchase, and your money will be willinglyrefunded in full.

THE LISSEN TRADITION FOR FINE QUALITYAND BIG VALUE FOR YOUR MONEY ISFULLY UPHELD IN THESE TWO NEWLISSENOLA PORTABLE GRAMOPHONES.

LISSEN LIMITEDFRIARS LANE, RICHMOND, SURREY.

Thomas N. Cole, Managing Director.

LISSENOLAMODEL No. 4.(Garrard motor)

14" x lli" x

C3 : 7 : 6

4

Wireless Magazine. August. 19281eifyl

Twenty -odd stations in one evening is not at all a bad performance for a cheap four -valuer,yet the point that struck J. Godchaux Abrahams most about the Five -pounder Four was itsgreat selectivity. Many readers of the " Wireless Magazine " will find it a receiver that will

meet their needs-especially if they are new to radio. Read all about it now!

NOW that you have seen theheading of this article you

know the most important thingabout the set to be described inin the following pages.

But there are a number ofspecial features about it that willappeal to you even if you arenot a beginner in radio-though it is for beginners, ofcourse, that the set is speciallyintended.

Great though the popu-larity of the three-valver isamongst beginners-thatwas evident from the successof the Music Charmer in theWIRELESS MAGAZINE forApril-we have no doubt that hun-dreds of amateurs would have pre-ferred to have started their radiowork with a four-valver, if only asimple enough design had beenavailable.

Well, not only can this set be builtfor (less coils, valves, batteries,and loud -speaker, of course), but theWIRELESS MAGAZINE Technical Staffdefinitely claim that it is the simplestdesign of a four -valve receiver yetattempted.

Actual Shape of Every Wire

This claim will be better appreci-ated when it is known that, althoughthe set is connected with stiff wire,

the length and shape of eachconnection is indicated full sizeon the blueprint.Nowhere, we believe, has an

attempt been made to do so muchfor the constructor as has beendone in this case by the WIRELESSMAGAZINE Technical Staff.

MAKES USE OF GOODQUALITY COMPONENTS

RECEIVES 24 STATIONS ONTHE LOUD -SPEAKER

NO SOLDERED CONNEC-TIONS

COVERS BOTH WAVE-LENGTH RANGES

EACH OF THE 39 CONNECT-ING WIRES SHOWN FULL

SIZE

ONLY TWO TUNINGCONTROLS

DESIGNED AND BUILT BYTHE "W.M." TECHNICAL

STAFF

TESTED INDEPENDENTLYBY

J. GODCHAUX ABRAHAMS

And now, in the leisure ofsummer days, is the time forthe beginner to build this finereceiver which will be worthits cost many times over in thewinter evenings when it bringsentertainment to the hearth -side from all over Europe, andeven further.

Question of PriceBefore going into actual

technical details of the Five -pounder Four, let us first lookinto the question of price alittle closer. Money has beensaved wherever possible, ofcourse, but nowhere at theexpense of electrical efficiency.

Here is an analysis of thecost of the original set :

Ebonite panel ... 8/-2 .0005-microfarad variable con-

densers, with dials ... 15/-2 dial indicators ....000i-microfarad reaction con-

denser ... - 5/-: ...H.F. choke 5/6Resistance -capacity coupling unit 4/ -Low -frequency transformer ... 15/ -Terminal strip ... 1/-7 -ohm panel rheostat ... 2/6Single coil -holder ... if -Neutralising condenser ... 5/-4 valve -holders ... 5/-6 -pin coil base ... 1/6.0003-microfarad fixed conlemer2-megohm grid leak with holder 1/6io terminals 5/ -Cabinet ... ... 16/IIConnecting wire ... 1/8Screws ... -/6

Total ... £4 15s. 3d.If this list is read in conjunction

with the detailed specification onpage 8 it will be seen that thecomponents are of good quality andrepresent the best value for money.

Full Size and Shape of Each Connecting Wire Shown on Blueprint !

5


The prices given apply, of course,to the original WIRELESS MAGA-ZINE receiver and the manu-facturers of the componentsused in that are mentioned firstin the brackets in each case.

Complete OutfitCo convert the Five -pounder

Four into a complete receivinginstallation it is necessary to addfour valves (44/-), coils for bothwavelength ranges (4.4./-), anaccumulator (16/-), a high-tension

The Five -pounder Four (Continued)

The Five- frequency amplifier, provided with a separate grid -biasPounder tapping, this being coupled by means of a transformer to

Fourwired (4) the second low -frequency amplifier, in the anode

up circuit of which is connected the loud -speaker.

H.F. Valve gives Greatly Increased SelectivityIn this arrangement the high -frequency amplifier with

its tuned transformer circuit gives the set a highdegree of selectivity. For this reason a four-valveris often of much greater utility near a local stationthan is a three-valver without a high -frequencyamplifier-the last gives sensitivity and selectivity.

Moreoever, in this case still greater selectivity is

EBONITEPANEL

'0001 MICRO -FARAD REACTION

CONDENSER

H. F.VALVE HOLDER

CENTRE -TAPPEDAERIAL COIL

HOLDER

NEUTRALISINGCONDENSER

'0005 MICROFARAD VARIABLE CONDENSERS

SPLIT -PRIMARY RHEOSTATTRANSFORMER BASE H F CHOKE

RESISTANCE -CAPACITY

COUPLING UNITANODE RESISTANCE.

25MEGOHMS,GRID LEAK:

2 MEGOIMIS

L. E. T RANSFOR ME RAPPROXIMATELY

4 TO I

POWER VALVEHOLDER

Isr. L.F. VALVE HOLDER

.0003 GRID CONDENSER 2 MEGOHM GRID LEAK DETECTOR VALVE HOLDER

All the components for the Five -pounder Four aredearly indicated in this plan -view photograph

obtained, without in any way complicating the controls,by utilising a tapped coil in the aerial -tuning circuit(see circuit diagram on left). The whole of this coilis tuned by a .0005-mfd. variable condenser.

GB- s

OriT+2

OrIT+1

LT+

battery (p6/-), and a loud -speaker (3o/ -)-say £12 los.for a complete outfit !

Combination of Valves EmployedEven the non -technical beginner will be

interested in the circuit of the Five -pounder Four,for it is representative of any straightforwardmodern receiver. The combination of valvesemployed is : (I) High -frequency amplifier, neutralisedand coupled by six -pin split -primary transformer to (2)the detector, which makes use of leaky -grid rectificationfor sensitivity and simplicity; reaction is taken to thesecondary of the high-frequency, transformer and thereis a resistance -capacity coupling to (3) the first low -

6

(Left )-Circuit ofthe Five -pounder

Four

Another view of theFive -pounder Four,with valves and coilsin position ready for

use


Ideal for the Beginner in Radio WorkIn the anode circuit of the first valve is the

primary of the split -primary transformer, thecentre tap of which is connected to the H.T.1-terminal. The top end of the primary is connectedback to the grid of the valve through a neutralisingcondenser, which gives the set stabilisation andgreater range.

Capacity -controlled ReactionTo the primary is coupled the secondary of the

transformer, which is tuned by another .0005-microfarad variable condenser. Reaction isobtained by means of a special winding coupled tothe secondary and connected through a smallvariable condenser (which controls it) to the anodeof the detector valve.

No efficiency is lost by not screening this split -primary transformer in a metal case-it is, in fact,more efficient than those that need screening. Thewindings are of the astatic type and, having only anegligiblc external field, no interaction with neigh-bouring components or pick-up from the localstation is experienced.

Importance of the High -frequency ChokeLeaky -grid rectification of the detector valve is

carried out by a .0003-microfarad fixed condenserand a 2-megohm grid leak. High -frequency cur-rents are prevented from leaking through to thelow -frequency portion of the receiver and so caus-ing interference by the insertion in the anode circuitof the detector of a high -frequency choke.

The coupling between the detector and the firstlow -frequency amplifier is provided by a resistance -capacity unit ; note that it has the following values,which should be specified when the complete unitis ordered : Anode resistance, .25 megohm(250,000 ohms) and grid leak, 2 megohms. It isimportant that these values should be adhered to.

Separate Grid Bias for each AmplifyingValve

A low -frequency transformer with a ratio in theneighbourhood of 4 to x is used to couple the firstlow -frequency transformer to the last valve. Notethat each amplifying valve is provided with aseparate grid -bias tapping. A rheostat is utilisedas an on -off switch to protect the valve filamentsfrom too sudden changes in temperature.

Before beKinning the construction of this setreaders are advised to obtain a copy of the full-sizeblueprint that is available for half-price, that is, 9d.post free, up till the end of the month if the couponto be found on page iii of the cover is used beforethat date.

Where to send your Postal OrderAddress your inquiry to Blueprint Department,

WIRELESS MAGAZINE, 58/61 Fetter Lane, E.C.4,and ask for No. WM 91; your copy will be sent byreturn of post. It is not essential to buy a full-sizeblueprint in order to build this set if the full-sizelayouts of the connecting wires are not required ;

.F746-

.0001 MFR.REACTIONCONDENSER

BASEBOARD

M.F. VALVEHOLDER

EuTR41..1.51114ConEIENIMA

TERMINAL STRIP10"01.

DIAL INDICATORS

0005 MFD.VARIABLE.CONDENSER

ARIALTUNING

COMEILILSER

WON, EARTH LTH LT -

.0005 MFR.VARIABLECOnoursER

" TUNING

0

WEL 16*Xe

I &MURK(WM9I

MA5TER RHEOSTATUSED AS 00-01T

SWITOI

0-

R.C.CEMPLIRLUNIT L.F. TRANSFORM(

0.05AMOREMOHR

REN5fARCE.

I - L.EVALVE

MOLDER

urL"E'At

Wrsi eIT.2. GB -1 RB-H EAT Lb -

47'©FLEA eAll r--;7

@0.

0 a. 0

MOTU. ALL WIRESARE 5110V1 fuLLSIZE sUggErilip

Tnc ntIRBLAs ONTHIS BLUEPRINT

If:'WLZ'ST,7 INCA

This layout and wiring diagram of the Five -pounder Fourcan be obtained as a full-size blueprint (on which the actualsize and shape of every wire is indicated) for half-price, thatis 9d., post free, if the coupon on page iii of the cover is usedby August 31. This blueprint, which is reproduced on good

stout paper, actually measures 37 in. by 16 in.

7


TheFive -pounder

Four

all the essential details are reproducedin these pages.

Before starting to do any part ofthe constructional work the reader isrecommended to get together all theparts. Remember that if you intendto wire up from the full-size layout ofconnecting wires you must use com-ponents made by the manufacturerswhose names are mentioned first inthe list of components.

Unusual LayoutLooking from the back of the panel

the components are laid out on theopposite way from standard practice.This was done after considerableexperiment and discussion as itsaved a number of awkward cross-over connections. Moreover, thelayout of the set as it is being wiredcorresponds closely to the circuitdiagram.

Constant reference to the full-sizeblueprint (or the reduced repro-duction on page 7) and the plan -view

The Five -pounder Four (Continued)

photograph on page 6 willenable even the newest

reader to recog-nise and place intheir proper posi-tions all the com-ponents, and they

will not beenumeratedn detail

here.The top

part of theblueprint acts as a drilling

one end of it firmly and then stretchit out taut. If it is pulled hard enoughit will stretch slightly but, more im-portant, it will also become morerigid and quite straight. It is im-portant to stretch only the wire andnot the insulated covering, as thelatter will crack under tension.

Now with a pair of wire -cuttingpliers cut off a piece of wire the samelength as connection No. 1 on theblueprint, allowing enough to make asmall " eyelet " at each end. Connectthis wire in position, and put a.

COMPONENTS REQUIRED FORI-Ebonite panel, 16 in. by 8 in.

(Resiston, Raymond, orBecol).

2-.0005-microfarad variable con-densers with 4 -in. dials (Ray-mond, Dubilier, or Igranic).

2-Dial indicators (Bulgin).I-.000x-microfarad reaction con-

denser (Bulgin, Cyldon, Bebeor Igranic).

1 -6 -ohm panel rheostat (Lissen orPeerless).

I-Single coil -holder (Lissen orMagnum).

i-Neutralising condenser, 65micro-microfarads (Bulgin orPeto-Scott).

4-Anti-microphonic valve holders(Ashley, Lotus, or W.B.).

1 -6 -pin coil base (Cason or Lew -cos).

I-.0003-microfarad fixed conden-ser (Lissen, Graham-Farish,or Dubilier).

I-2-megohm grid leak with holder(Lissen, Graham-Farish, orDubilier).

I-High-frequency choke (Lissen,Wearite, or Igranic).

I-Resistance-capacity couplingunit with .25-megohm anodeesistance and 2-megohm

1111.11,11111

THE FIVE -POUNDER FOURgrid leak (Lissen, Trix, orDubilier).

I-Low-frequency transfo r m e r(Igranic type F, R.I. andVarley, or B.T.H.).

1-Ebonite terminal strip, io in.by 2 in. (Raymond, or localdealer).

To-Terminals, marked :-Aerial,Earth, L.T.±, L.T.H.T. 1, H.T. +2, G.B. -1,G.B. -2, L.S.-(Belling-Lee, type M).

2-Centre-tapped plug-in coils(Lewcos or Atlas, No. 6o and15o).

2-Si-pin split -primary high -frequency trans f or mers(Lewcos types, BSP5 andBSP2o).

1-Cabinet, with 9 in. baseboard.2-m -ft. coils insulated wire

(Glazite).22-y2 -in. wood screws.12 -3/4 -in. wood screws.

Short length of flex.

(Only components made by thefirm mentioned first in the bracketsin each case can be utilised if properuse is to be made of the full-sizeblueprint.)

IMO

template for the necessary panelholes, while the lower partcan be utilised as a base-board layout. If the blue-print is folded and stuck onthe back of the panel andon the upper face of thebaseboard there is nochance of going wrong.

As soon as all the com-ponents have been securedfirmly into position, wiringup can be started, and herethere is less danger of goingwrong than there is in thebuying of the components.

Uncoil one of the lengthsof Glazite and bare an inchor so at each end, clamp

ff

SLOT ArtTO TAKE

PR/EL /6.r8.Details of cabinet for the Five -pounder Four

8

line through No. 1 on the blueprint.Carry on with wires Nos. 2, 3, 4,

etc., marking them through on theblueprint as soon as they have beenplaced in position on the set. In thecase of shaped leads bend the con-necting wire exactly to the shapeindicated on the blueprint and it willfit into position without furtherbending, although it may be necessaryto give a slight twist to the "eyelet"at each end.

No Soldered ConnectionsNotice that there is no need to

solder any connections, but all theterminals should be screwed downtightly with a pair of pliers. Con-nection No. 39 is a flexible lead.

Wireliss Magazine. August. 1928

The Simplest Yet AttemptedThe necessary coils for use in the

Five -pounder Four are listed with therest of the components. For thelower broadcast waveband use theNo. 6o coil and the BSP5 trans-former, while for the higher wave-band use the No. 150 coil and theBSP2o transformer.

Not quite so easy is the choice ofvalves, but the following may betaken as an approximate guide.Two-, four-, or six -volt valves can beused, but they should conform to thefollowing standards :The high -frequencyamplifier should havea n impedance o f20,000 to 3 o, 000ohms, while the de-tector should havea n impedance_ i nthe neighbourhoodof 6o,000 to 8o,000ohms.

Any valve roundabout To,000 to15,000 ohms will dofor the first low -frequency amplifier,

wit

.1

47

sound (not a howl orwhistle) is heard from theloud -speaker; this indicatesthat the set is on theverge of oscil-lation and ina very " live "condition forreceivingsignals.

Now turnthe twolarge dials slowly

1

/6Panel layout of the Five pounder Four

while the last valve should be of thesuper -power type with an impedanceof 6,000 ohms or less. Actually inour tests we used the following Six -Sixty two -volt valves: SS2I0HF,SS2IoRC, SS2IoLF, and SS215P.

As regards batteries connect theseup as follows (remembering that red ispositive and black is negative) : ToL.T.-1- and L.T.- connect an accum-ulator of the same voltage as thevalves to be used. To H.T. I applyabout 8o to 90 volts and to }LT. -I-the lull 120 volts of the battery. ToG.B. I apply 3 to 6 volts negative,and to G.B. -2 apply 6 to 12 voltsthis depending upon the valve used.

Connect both G.B. + and H.T.-to L.T. - (this, of course, saves twoterminals). If two 6o -volt high-tension batteries are used connectthe negative end of one to the positiveend of the other and regard theremaining negative and positive polesas those of one 120 -volt battery.

To operate the set connect up theaerial, earth, and a loud -speaker.Now turn round the knob at the left-hand side of the panel; this switcheson the valves and makes the receiverready for action.

Next, move the small right-handknob until a slight rustling or hissing

Wave.length Stationmetres1,765 Radio Faris ..1,604 5XX1,480 Moscow (3)1,380 Motels. ..

556 Budapest ..649 Milan VIgentino517 Vienna ..508 Brussels491 505

a 485 Berlin ..470 Langenberg461 Oslo (faint)

throughout their range, in such away that the rustling or hissingsound is always heard from thelcud-speaker, until a transmission ispicked up.

When this occurs, readjust thereaction condenser (small right-handknob) until the clearest results areobtained.. If the quality is very badreadjust the grid -bias voltages; anincrease in the amount of negativebias applied will in most cases effect acure.

As soon as one station has beenfairly well tuned -in try neutralisingthe high -frequency valve ; this willmake the set easier to manage.

Keep the station tuned -in and re-move one of the filament connections

Anotherview of the Five -pounder Four

from the holder of the high -frequencyvalve, say wire No. T.

Do not remove the valve, but turnthe vanes of the neutralising conden-ser on the baseboard until signalsbecome quite inaudible; then thecapacity of the valve has beencompletely neutralised. Replace wireNo. I and carry on as explainedpreviously. If this neutralisation iscarried when the low -wave coils arebeing used it -may be necessary to re -neutralise on the higher waveband.

Note the Dial ReadingsWhen a station has been picked up,

make a note of the dial readings-that of the left-hand condenser dial(which tunes the high -frequencytransformer) is very critical, but willremain constant under all conditions.The reading of the right-hand dial(which tunes the aerial circuit) willvary with different aerials.

For quick searching note thedifference in the readings for anyparticular station of the two dials,then keep this difference (approxim-ately) throughout the entire rangewhen turning the dials.

LOG OF FIVE -POUNDER FOUR(TESTED JULY 1st -3rd, 1928, by J. GODCHAUX ABRAHAMS)

LONG WAVES (COIL NO. 200)Wass -Aerial S.F. length Station

Cond. Cond. 'leave.. 155 122 1,250 Koenigswusterhansen

135 105 1,153 Kalundborg116 90 1,100 Warsaw112 84 1,060 Hilversum

MIDDLE BROADCASTING BAND (COIL NO. 60).. 180 178 428 Frankfurt .... 176 164 6 422 Kattowitz .

.. 172 158 380 Stuttgart.. 168 152 e 375 Madrid EAJ7 .

.. 164 150 d 368 Leipzig.. 160 146 364 2L0 London .... 148 128 345 Barcelona EAJ1

142 126 337 Copenhagen

AerialCond.

S.F.Cond.

106 82100 8094 7286 64

132 114130 112126 110124 105120 100115 98110 90104 80

Gleiwitz, Breslau, Lille, and Cologne were also picked up, but with the use of a smaller coll.a Only heard when 5GB closed down. e Heard when Stuttgart had closed down.

Wan somewhat spoilt by Frankfurt. d Only when 2L0 was not transmitting.(FURTHER OOMMENTS WILL BE FOUND ON PAGE 78).

9


HALYARD'S Chat on the Month's Topics

Wireless GramophonicsALITTLE wireless know1,3dge is

a-wait a minute-very usefulthing sometimes, now isn't it?

I certainly thought so one after-noon recently, when I had what wasto me a new, and rather novel,experience. My intentions thatafternoon were to visit the annualsports of a school in which I have alive interest, in the shape of a boy.Rain, however, caused a postpone-ment of the sports, so I turned in tothe nearest cinema.

The music in this cinema that after-noon was provided by apparatus of atype now becoming rapidly familiarto wireless enthusiasts, namely, agramophone with electrical pick-upfollowed by amplifiers, the amplifiedsound from the gramophone recordbeing reproduced by loud -speakers.

During the performance the soundsfrom the loud -speakers graduallydiminished in volume until theyfinally dwindled away altogether. Ithought I recognised the symptoms,and I think you would have done so,too.

After the performance I went tohave a look at the wireless gramo-phonic apparatus. A very troubledcinema operator was going over thewires to the two loud -speakers onthe stage. I asked him what kindof an accumulator he was using tolight the filaments of the valves.

" A six -volt accumulator," hereplied.

" Do you mind letting me have alook at the valves with the accumu-lator turned on ? " I asked.

He did so and, as I thought, theaccumulator was run down. Therewas scarcely enough glow in the valvesfor the dullest of dull -emitters.

I suggested trying another accumu-lator. On our doing so, the volume

of sound from the loud -speaker wassplendid.

The operator was very puzzled toknow how the accumulator had cometo fail so badly in the middle of itsweek's work. If he had our know-ledge of wireless he would know that

New and rather novel experience

accumulators do occasionally playstrange tricks of this kind, wouldn'the?

Titles for TalksIf there is anything in the old

idea that your ears burn when some-body is talking about you I shouldthink that certain of our programmebuilders and broadcast talkers musthave had red-hot ears on manyoccasions during the past few weeks.Really it is astonishing how much has

If there is anything . . .

been and is being written and saidabout our broadcast talks.

Most of the criticism of our talks isof the destructive variety. Occasion-ally we do get a little criticism of theconstructive type, as for example,a recent suggestion that, if only

10

Sketches by GLOSSOP

attractive titles were to be given toour broadcast talks, all would bewell and we should find ourselvestaking far greater interest in thosetalks.

I have been rather intrigued by thissuggestion and I should be veryinterested to hear your opinion of it.Do you think that you would be muchmore tethpted to listen to a talk onAmerican motor cars say, if the titleof the talk were given as " RattlingGood Things from the U.S.A." ?

Again, would you be more likelyto listen to a talk on Wordsworthif the talk were announced under thetitle " The Poet with the Big Out-put."?

Sound TheoryI had just finished reading an

interesting article on the acoustics ofreception when George came in. Fullof my newly -acquired knowledge,I fired this question at him

" What is the best way to obtaintonal fidelity, George? "

" Gargle night and morning withsalt and water," replied George.

Now if my technical adviser hasone fault above all others, it is thisevasion of my technical questions.Usually he evades my questions inorder to gain time to think. On thisoccasioh however, I was in no moodto be trifled with so I said :

" Don't be foolish, George. Youknow I am referring to tonal fidelityin wireless reception. To obtainsuch a desirable quantity, the properposition of the loud -speaker mustbe determined from a careful con-sideration of the acoustical proper-ties of the reception room. A loud-speaker should never be put so thatit points across the breadth of a

Sound theory

narrow room. It should point downthe length of that room."

" So that everybody can see thepoint."

"Damping should be moderateover the whole room, George. Softmaterials such as rugs, curtains, andupholstered furniture damp sound.Flat, hard surfaces reflect sound,whichis bad."

"That's why a loud -speaker neverworks as well in a room full of bald-headed

" Be quiet, George, and pleaselisten. Damping should be greatestat a point directly opposite to theloud -speaker. Hence a soft hangingof some kind, or a rug, placed on thewall facing the loud -speaker mayimprove the quality of reception."

" I know a wireless enthusiastwho hung a large tapestry on thewall opposite his loud -speaker."

"Did it improve the tonal fidelity,George ? "

" I'm not; sure about that, but itcertainly hid a nasty hole in theplaster."

Taking More RisksWhat kind of notice do you take of

thunderstorms these days? Are youswitching off your set when atmos-pherics become troublesome, or areyou taking more risks than you usedto do ?

I do not know whether it is a casewith me of familiarity breeding con-tempt, but just lately, I seem to havebeen risking a great deal more than

.previously with regard to thunder-storms.

Possibly this increased daring ofmine started on the afternoon ofDerby Day. I could not go to theDerby, but I did manage to snatcha few minutes from a busy day tolisten -in to the great race. As soonas I switched on, the banging andcrackling of a severe thunderstormcommenced. I was more than a little


afraid of it, but when I heard thecommentator tell us that Epsomwas free from the thunderstormthat somebody or other had pro-phesied for the Derby this year, Imade up my mind not to let mythunderstorm do me out of my recep-tion of the Derby.

It was pretty bad though, really.The next day I read of a bad thun-derstorm which had occurred theprevious afternoon some fifty milesaway. So I know now just whatnoise a thunderstorm fifty miles awaycan make in my wireless receiver, and,

Taking more risks

having that knowledge, I am takingmore risks than before, perhaps.

A Wireless Log .The last time I went on a shopping

expedition to the city, my attentionwas drawn to a wireless writing -pad in a stationer's window. Iwonder if you have ever seen sucha thing?

At the top of the pad were the

A wireless log

words "London calling the BritishIsles" and a picture of Big Ben.The pages of the pad were of differ-ent lengths. On the bottom of eachpage was a heading-well--scarcelya heading at the bottom of a page,perhaps, but anyhow, there wereprinted words at the bottom of eachpage indicating what was to bewritten above.

By pushing my nose close to thewindow pane, I was able to countup the pages. There were five pagesallotted. to " Stations Heard," oneto " Records of Renewals and

Additions to Set," five to " GeneralNotes," and one to " Press Cuttings."

Rather an optimistic person whodesigned that log, wasn't he ? Howwould the proportion of five pagesof "stations heard" to one page of"renewals and additions to set" suityour book?

Still, the idea of a wireless log likethat seemed good to me and I reallybelieve I should have bought that oneI saw if the shop had not been closed.

.

StuntsAre you in favour of the re -intro-

duction of " stunts " into our broad-cast programmes with the idea ofbrightening things up a little?

You remember the broadcast" stunts " of a year or two ago,don't you? There was the stuntbroadcast of a diver speaking fromthe bed of the river Thames. Anotherstunt, and a very jolly one, was thebroadcasting of feeding time at theZoo. Then there were severalstunt broadcasts from aeroplanes.

I wonder what has happened to thestunt department of the B.B.C.? Whydid it cease to stunt? Was it becausethe stunters ran out of ideas, or wasit because the B.B.C. officials cameto the conclusion that we were tiredof stunts? Of course it might havebeen' that somebody high up heldthe opinion that stunts were not goodfor us.

Anyhow, there is no stunt depart-ment at the moment, and the questionis whether we want its revival or not.What is your opinion ?

If we were to ask for the re -intro-duction of stunts, it would be ratheran idea for each one of us to suggesta jolly good broadcast stunt. Hereis my suggestion-the roar of NiagaraFalls, promised to us some time backbut never broadcast to us, as far asI remember. What is your stuntsuggestion ?

Brightening things up a little

Do Not Miss the Special Gramo-Radio Section on page 47 !

11


Under My Aerial (Continued)

It was like this

One UCWhat do you think happened last

week, of all things? George and I paida visit to one of our broadcastingstations. It was like this. I hadan appointment at-er-let's call itTUC, you will easily recognise thestation if you have ever been to it,and I thought it would be a goodthing for George if I took him with me.

" You know iUC pretty well,don't you ? " asked George as wewalked along a busy street towards thestudios.

" Yes. I've been there manytimes and I once spoke from there,you remember? " I replied.

"That was a couple of years ago,wasn't it? "

"Yes, George.""They never asked you again, did

they ? "" As a matter of fact, George, I

expect to speak from 'ITC again atthe end of the month," I repliedwith some asperity.

When we reached the studio build-ing, I led the way along a dark corri-dor, round a corner, down a flightof stairs, round another corner, downmore stairs, round more corners anddown more stairs until there were nomore stairs to go down.

" Broadcasting at iUC is appar-ently at a pretty low level," remarkedGeorge.

A boy from " Inquiries"approachedus. Looking at George, he said :

"Audition, sir ? "Before George could think of a

suitable reply, I gave the name ofthe official I had come to see.

In a few minutes we were in therush and turmoil of a broadcastingstation. We saw the studios andwe talked with several of the B.B.C.officials.

Altogether, we had a good timeat iUC, and I am glad to say thatGeorge has shown a little more res-pect for me since our visit. If heshows the least sign of getting a bituppish, all I have to say now is :

" Audition, sir? "You see there is nothing annoys

George more than to be taken for amusician.

A Better GaugeHave you ever written to the B.B.C.

to tell them whether you have likedor disliked any particular programmethey have broadcast? I doubt if youhave, any more than I have.

It is really quite astonishing howfew of us write to the B.B.C.; indeedthe reticence of the average listenermust surely be the greatest difficultyour programme builders have tocontend with. Those who are con-cerned with the arrangement of ourbroadcast programmes wouldwelcomenothing more than a reliable meansof gauging the manner in whichtheir programmes are received.

In America, of course, they havethe " applause card," and I haveoften wondered why something of thesame kind is not tried in our country.What I would like to suggest is thata packet of fifty-two "applausecards," one for each week in the year,be given to each one of us when wetake out our yearly licence.

My idea is that one of these cardsshould be used for one particularbroadcasting station on one particular

Really quite astounding

evening in the week to which thecard applies, the station and even-ing to be at our choice. On the cardwe should state the item of the pro-gramme we had liked the best, andthe item we had liked the least. Weshould then post the card.

LOOK OUT NEXT MONTH -FOR PARTICULARS OF ASCREENED -GRID THREE,VALVER. IT HAS SOMESPECIAL FEATURES THATWILL APPEAL TO EVERYHOME CONSTRUCTOR.

12

If some regular system such as thiscould -be adopted our programmebuilders would have a far bettergauge of the listener's opinionsthan they have at present and Ithink that better programmes wouldquickly result.

Quick WorkWhat is the quickest time in which

you have put together a three -valvereceiver?

I have just assembled a three -valve set for test purposes in a littleover three hours, and I am certain

0"EwE LL.E211

Quick work

that I could reduce that time veryconsiderably if I made an effortto work against the clock.

In building this three -valve re-ceiver, I used a horizontal baseboardand a vertical panel screwed to anedge of that baseboard, and I do notthink I ever appreciated the modernbaseboard method of assembly somuch before. It really is a conven-ient method, much more convenientthan the old back -of -panel methodand far and away the best methodwhen it comes to quick work.

My three hours spent in makingthis set included a certain amount oftime spent in hunting about for aconvenient baseboard and an oldpanel. To get my baseboard I hadto knock a box to pieces, but Ifound an old panel just the rightsize amongst my wireless junk.

I had some trouble in fixing aterminal strip at the back of the base-board, but when that was done, Itackled the wiring -up with greatenjoyment. As the receiver was fortest purposes only, I did not use asoldering bit in wiring up.

This test receiver has been givingexcellent results. I only hope thatit will give the same excellent resultswhen it is built into the fine cabinetI am having made for it. Sometimesthey don't, as perhaps you know fromexperience. HALYARD.

4,

IWireless Magazine, August. 1928

SOMe"HOMCAdclitions toThe CHUMMY FOUR

FOR the benefit of those who havenot previously heard of it, let us

say at once that full constructionaldetails of the Chummy Four weregiven on pages 399-406 of the Juneissue of the WIRELESS MAGAZINE andfurther notes were published onpages 483-5 of the July issue.

extraordinary for a frame -aerialreceiver which is completely self-contained and which is so cheap-thecomplete set of parts, includingvalves, batteries, and a cone loud-speaker, costing only iI5 or so.

after remedying it obtained on theloud -speaker thirty-three stations ina period of three hours. And remem-ber that this was without any elabor-ate aerial -and -earth system !

In writing later, to give us per -

FULL CONSTRUCTIONAL DETAILS OF THE CHUMMY FOURWERE GIVEN IN THE JUNE ISSUE OF THE "WIRELESS MAGA-ZINE." BACK NUMBERS ARE Is. 3d. EACH, POST FREE.

Tested during one evening by Mr.J. Godchaux Abrahams, the well-known authority on European broad-

casting affairs, twenty-threestations were picked up on theloud -speaker and each trans-

mission was defin-itely identified. Ina subsequent testa member of the"W.M." Staff

received thirty-one sta-tions in an evening,though all of these werenot identified.

If any further proofis required of theenormous range of thishandy four-valver, it is

THIS SET WILL RECEIVE THIRTY STATIONS ONTHE LOUD -SPEAKER, AND THE COST OF ALL THEPARTS FOR A COMPLETE OUTFIT IS ONLY ABOUT L15

And what exactly is this ChummyFour, of which so much fuss is beingmade ? Well, it was at the time of itspublication the first screened -gridvalve portable to be put before thepublic by any radio journal and is, asfar as we are aware, the only set ofits kind in existence.

The results it gives are really

provided by the letterfrom a WIRELESSMAGAZINE readerreproduced on page 15.

Here is a case of areader who, after writinga letter of complaint,found a small fault inhis Chummy Four and

13

mission to reproduce his letter photo-graphically exactly as it was receivedby us, this reader says : " Do yourealise that you have made a mistakein publishing details of this set?Whoever makes one of these will

never want another set !"As it was originally ar-

ranged the Chummy Four hada rheostat for controlling

Although the weight (30 lb.) of theChummy Four necessitates aslight angle of inclination on thepart of the person carrying it, thecase swings freely by the side

of the legs

This photograph shows the position of the headphone jackand the jack switch for using an external H.T. supply

Wireless Magazine. August, 1928

the filament cur-rent of the Cossorscreened -gridvalve and a push-pull on -offswitch for con-trolling all fourvalves at once,but experiencehas shown thatsuch critical con-trol of thescreened -gridvalve is not reallyessential.

RheostatIt was therefore

decided to dis-pense with thepush-pull switchand control allfour valves withthe rheostat, thisbeing used as anon -off switchwhich protectsthe filamentsfrom too sudden changes of temperature.

A number of readers also asked for somemodification for using a pair of headphonesas well as the loud-speaker-presumably forD.X. work.

Several other useful modifications pre-sented themselves and the WigsMAGA-ZINE Technical Staff decided to make suchalterations as would be of the greatestutility to the operator.

Range and Volume UnaffectedIt should be very clearly understood, how-

ever, that these alterations or modificationsin no way affect the performance of theset. They will not make the Chummy Fourbring in more stations or louder signals, butthey do make it handier for use in the home.

The alterations that have been made

cnEcnth LsI e'LWIT2'

Cla la OM OW Of IRAPIL TO Un ,AP On OW'S

uu,+90 -

liF (HOKE, IIETOL BO '-' ''l o A.fr[.

1lip 0,n rolIW'.4,1-4COMILIroLli

o 16.11 aftr4, .==- I,

101,Zl11,601.11 .II 11W 4euk

iii

61.re. al

"06 ,..60, .olLTO 6TI

'' gi. 1 ri°8.43,- I. ,14

sc"..nal .,,

'-'1n

oa 0 :0 V PAII(1.IC %13

- r- mil-KGB;

ik5 TO PIT-

..,

011

00 02 FD.

.

- -1

1"

111 morn:....=k. 1 45

,06

III 0 C1111 ,ONT10tri or II BIN.,f,B0AllkKLTAI. box

--'-', TUFV,Z.PoN, 0,---,o

eS./

A. 0 0 t:,

0 0 0 0 t A 0

,1

.m.-.0111U w6.61. 01.11,- *,,-11.....

OUTPuT `.1,, OUL .

i'vra!LX,411,1,14.1,,r7,711nn,.1..1".

.

This revised layout and wiring diagram (No. W.M.80A) can be obtained as a full-sizeblueprint for half-price, that is 9d. post free, up to the end of August if the coupon on

page iii of the cover is used. The original blueprint (No. W.M.80) is 1/6 post free

"Home" Additions to the Chummy Four (Contd.)

in the "Home" edition of the Chummy Four are, then, asfollows :

Alwaysready "Home " Additions and Modifications

for (i) Addition of terminals for utilising ordinary aerial anduse earth for experimental work.

is the (2) Provision for use of headphones or an external loud-Chtunmy

Four !speaker. (In the " W.M." experimental laboratory theChummy Four will operate a moving -coil loud -speakerquite successfully.)

(3) Use of rheostat as on -off switch to protect valve filaments.(4) Provision for using external source of high tension, such

as high-tension accumulator or mains supply unit.Those wishing to convert their existing models of the

Chummy Four inthis way will needthe followingextra compon-ents:

3-Terminals,marked : Aerial,Mid -tap, Aerial(Belling -Lee).

3-Small plugs andsockets, 2 redand I black(Lectro Linx).

I-Plug and jack(Lotus, No. 2).

1-Double-polejack switch(Lotus, No. 8).

These additions,of course, meanthat a new wiringdiagram isrequired and forthis reason a newblueprint (repro-duced on theleft has beenprepared. This is

JACK FORPRONL.5 ORE XT ERR ALLOUD-SPEAKER

Here is the Chummy Four with the " home " additions, described in detail inthese pages. The phones are Brown's Featherweight type

14


Thirty Stations on the Loud/speaker !No. W.M.8oA (the original Chummy Four is No. W.M.8oand is still retained) and can be obtained for half-price,that is 9d. post free, up till August 31 if the coupon onpage iii of the cover is used by that date. Note thatthe full price of is. 6d. is now charged for blueprintNo. W.M.80.

Where to Send Your Postal OrderAddress your inquiry to Blueprint Department,

WIRELESS MAGAZINE, 58/61 Fetter Lane, E.C.4, andyour copy will be sent by return. By the way, newreaders who want the original constructional article onthe Chummy Fourcan obtain copiesof the June issuefrom the Publisher,at the aboveaddress, for Is. 3d.each, post free.

Some moredetailed explan-ation is needed re-garding the pro-vision for using anexternal source ofhigh-tension,although theremainder of themodifications areself-explanatory.

Cheaper H.T.It was thought

that those who hadavailable a cheapersource of supplythan dry batteries-that is, a high-tension accumu-lator or mainssupply unit-would prefer toutilise it if possiblewhen operating theChummy Four athome.

The adaptation

is not difficult.In the set thereare two high-tension positiveleads, one supply-ing 120 volts or soto the anodes ofall the valves andthe other supply-ing 8o or go voltsto the screeninggrid of the Cossor

How the headphones are held in the lidscreened -grid valve.Now obviouslythese two leadscould be taken to adouble -pole switchwhich would con-nect them towander plugs onthe batteries insidethe case or to twoterminals to whichan external sourceof supply could beapplied. The nega-tive lead can, ofcourse, remain com-mon to bothsupplies.

Thiaphane.Sovthall /339.

JOINERYMANUFACTURERSTIMBER MERCHANTS

AVERY & VINCENTIF VINCE NT,

Hart ingt on Road.

SOUTHALL. MIDDX.

The Bditor,The ,tireless Magazine,58/61, Potter Lane,London.3.0.4,

Dear Sdr,Re "The Chummy your";.

Established /897

CONTRACTosTS ToH.14.0FP.CE O WeAlt(S.

THE WAR Orr ECoup,. CovnTIT

Jun. 26th.1928.

As I have previously written you complaining about theperformance of this set I think it only right that I shouldlet you know that rhos,e now remedied the fault and thatthe performance of the set is now all that can he desired.

On Bridal,' last, Jun. 22nd., beftmen 9-30.p.m. and12.30.a.m. I tuned in on the loud speaker, thirty threestations including 2.L.O. and 5.0.2., and when I say on theLoud Speaker I mean that the majority of the stations coaldbe heard upstairs when the set was working downstairs.

The only other set that I have had that Le as *sayoperate as this one was a seven valve Super -hot and thateasily lost on the score of Noisiness end Purity of Tone.

Up to the moment I have had nothing to compute with thissat in respect of Range, Simplicity of 'rutting amt orQuality of Reproduction and I Congratulate you.

Yours truly,

P.S. This is my first experience with n Screened Or;4

When you have built your Chummy Four try to beat this record

15

Three SocketsThe three sockets

at the top right-hand corner of thereceiver are there-fore arranged in thefollowing orderfrom left to right :(a) negative, black,(b) 8o or 90 volts,red, (c) 12o volts ormore, ,red. Thesesockets are in usewhen the knob of thejack switch is pushedin. When the knob

is out the high-tension batteries in the case are in circuit;on no account pull the switch knob out when an externalsource of high tension is connected to the sockets.

Jack for Headphones or External Loud -speakerImmediately underneath the jack switch for external

high tension is the headphone jack (this can also beused for an external loud -speaker as itsoperation cuts out the cone loud -speakerbuilt into the set).

For portable work, a pair of phones canbe arranged inside the lid as shown by thephotographs reproduced in these pages.


Some "Home" Additions to the Chummy Four (Continued)

COMPONENTS REQUIRED/-Ebonite panel, 16 in. by 8 in.

(Resiston, Becol, or Raymond).-Metal screening box with lid

(Magnum or Formo).2-.0005-microfarad variable conden-

sers (Formo 1928 Log).2-Vernier dials (McMichael).x-.0002-microfarad Bebe condenser

with small dial (Cyldon).1 -7 -ohm panel rheostat (Lissen,

Igranic, or Peerless).I-Screened-grid valve holder (Burn -

dept).2-2-microfarad fixed condensers

(Lissen, Dubilier, or T.C.C.).r-Anode coil as specification (Burne-

Jones).r-High-frequency choke (Omnora,

Wearite, or Igranic).I-Low-frequency transformer, ratio

4 to I (Mullard).3-Anti-microphonic valve holders

(Redferns).I-On-off switch (Bulgin Midget,

Lotus, or Lissen).I-Pair small panel brackets (Mag-

num, Cameo, or Bulgin).2-2-raegohni grid leaks with clips

(Loewe).I-.005-microfarad fixed condenser

with clips (Loewe).I-.0003-microfarad fixed condenser

with clips (Loewe).I-.25-megohm grid leak with clips

(Loewe).1-Ebonite strip, 2i in. by if in.

(Resiston, Becol, or Ready Radio).

6111411.101M NM *NOM NV M

FOR THE CHUMMY FOUR2-Ebonite washers, in. bore and

+ in. thick (Ready Radio).6-Lengths Glazite.3-yards thin rubber -covered flex

(Lewcos).2 -6o -volt high-tension batteries

(Lissen).2 -9 -volt grid -bias batteries (Lissen).2 -2 -volt accumulators (C.A.V. type

2NS9, with jellied acid).1-Loud-speaker unit (Goodman

doubt -acting).1-Piece gold -finished cone paper

(Goodman).1-Piece rubber sheet, x ft. square

(any sixpenny stores).io-Wander plugs, 6 red and 4 black

(Igranic).xo-Indicating tabs for flexible wire,

marked : two H.T.+ , oneH.T.-, two G.B. - , one G.B.+,one L.T.+ , one L.T. -, oneL.S. + , one L.S. - (Bulgin),

1-Cabinet with baseboard, batterybrackets, loud -speaker front andback (Ready Radio).

2-Oz. No. 28 -gauge d.s.c. wire forframe aerial (Lewcos).

8-Ebonite strips, 11 in. by x in.(Ready Radio).

12-6B.A. 1 in. round -head screws withnuts (Bulgin or Ready Radio).

36-+ in. No. 3 brass wood screws(Bulgin or Ready Radio).

2-Ii in. brass wood screws (Bulginor Ready Radio).

3-Dial indicators (Bulgin).1-Station log, small (Bulgin).

This is the original specification as pubMagazine

The earpieces of the phones must not be too thick or itwill be impossible to close the lid. We found a pair ofBrown's Featherweight (type F) phones verysatisfactory for this reason. No attempt has beenmade to count the number of stations that can bepicked up on a pair of phones-they roll in righton each others' heels right round the dials !

No Difficulty in Getting ResultsFrom the correspondence we have had with

readers regarding this set during the past fewweeks we are certain nobody building it up willhave any trouble in getting good results if theoriginal specification is adhered to. Constructorswho use parts other than those recommendedmust not blame the WIRELESS MAGAZINE if theydo not get satisfactory results.

Almost the only trouble that is likely to arise isa high-pitched and not very obtrusive low -frequency whistle. If this occurs reversing theconnections to the low -frequency transformer isalmost certain to effect a cure.

Use of Ordinary Aerial and EarthWhen it is desired to use an ordinary aerial

and earth system for experimental work, makethe necessary connections to the terminals at thetop left-hand corner of the receiver. Connectthe aerial to the left-hand terminal and the

ished in the June issue of the " Wireless

earth to the middle terminal. In thisway the frame aerial in the lid isutilised as an aerial coil.

SeeingDistortion

ONE of the oldest radio hints isthat of putting a milliameter

in the plate circuit of a valve sus-pected of distorting owing to grid -voltage overload. The hint is notalways properly understood, orproperly applied, and this despitethe fact that it is something of achestnut.

A mistake is made in believingthat when everything is ready fortest, with the meter in circuit, theneedle should remain rock -steadyif there is no overload.

Slight Swing InevitableActually, with a good meter, a

certain' amount of needle swing isinevitable. If a set passes a totalof io milliamps, for instance, aswing of from 91/2 to io y2 milliampsis allowable, and does not necessarilymean distortion. Serious jumpingof the needle at large grid voltage

swings should be corrected, however, by alteration ofH.T. or grid -bias voltage values.

H F.CNOKE ANODE COIL

ANODEREACTION CONDENSER

CONDENSER \

BLOCKINGCONDENSERS

L.F.TRANSFORMER -

ANODECONDENSER

& GRID LEAKS

POWER VALVE'

!sr L. F. VALVE'

DETECTOR"VALVE

SO -VOLT HT. -BATTERY

SCREENINGBOX

B. MARSHALL

HE COUPLINGCONDENSER FRAME

CONDENSER

2 -VOLT ACCUMULATORSIN PARALLEL (C.AN)

The arrangement of all the parts in the Chummy Four is clear from thisphotograph. It consists of a high -frequency amplifier, a detector, aresistance -coupled low -frequency amplifier and a transformer -coupledamplifier. This shows the set before the " home " additions are made

RHEOSTAT

H. F.VALVEHOLDER

TWO 9 -VOLTC.B. BATTERIES

CONELOUD -SPEAKER

60 -VOLT H.TBATTERY

16

TWO

THERE are many who regard-quite mistakenly-the summer

as a kind of dead season for thereception of anything but the trans-missions of the local station or thoseof 5X X and 5GB. Actually there isno more interesting time of the yearthan the summer for wireless recep-tion at long range. True, one does notfind stations roaring in all round thecondenser dials, as is the case duringthe darker months. Nor is signalstrength, taken as a whole, so greatas at other times of the year.

More Difficult to GetStations, are in fact, rather more

difficult to get in summer time, andtherein lies one of the main charmsof reaching out at this season. Inwinter almost anything that is fit tobe called a wireless set will bring inin some kind of fashion severalstations besides the local and thehigh -power.

It must, indeed, be a poor thingthat will not enable one to receive,say, Langenberg, Frankfurt, or Ham-burg on the medium waves, or Radio -Paris, Motala, or Hilversum on theupper band. But in summer, successcan be achieved only if the apparatusis really up to the mark.

And not the apparatus only; a good

`Wireless Magazine, august, 1928

deal depends upon the operator. Inwinter time stations are easy to find.As you turn the dials, you suddenlyhear speech and music at quiterespectable strength and no greatskill is needed to bring them up tothe desired -volume.

In summer, a distant station maybe so faint, when first picked up, thatit is easy to pass it over altogether;and, if it is heard, a certain amount ofskill is required to tune it in properly,without allowing the set to oscillate.As a rule, though, transmissions thatare very weak are not worth seriousattention, if one wishes for repro-duction of fine quality. One maytune them in occasionally as a matterof interest, or to test one's skill andthe efficiency of the. apparatus.

Keep to Powerful StationsBut, if we are in search of genuine

alternative programmes, that is,programmes that are thoroughlyworth listening to, the soundest of allrules for summertime work is toconfine oneself to the more powerfulstations. The reason is this. Atalmost any point on the broadcastband, with an efficient set broughtinto a sensitive condition, one mayhear mush or commercial Morsesignals, some so faint as to be hardly

17

audible, others strong enough to bea nuisance.

In summer time, too, electricaldisturbances are frequent, so that,even if grinders and crashes areabsent, there are always tiny atmo-spherics from distant storm centres,which become audible if the receivingapparatus is unduly sensitive.

Unwelcome BackgroundInterference from all these sources

is not noticeable so long as thestrength of the desired signal isgreater than that of the undesired.If we try to work up a very faintbroadcast transmission, we shallprobably bring up too an unpleasantbackground of interference from someof all of the sources mentioned.

Some of the winter stations willcontinue to be good friends to usduring the summer. The big Ger-mans, for instance, can be reliedupon on most nights on the mediumband, and late in the evening theSpanish stations come through withsplendid strength and quality. InSpain the evening does not beginuntil about ten o'clock or end untilthe small hours; hence the Spanishstations are to be found at work laterthan almost any others in Europe.

But Spain and Germany, are not


Summertime D.X. Work ! (Continued)

the only countries to which we canlook for summer entertainment.France, Italy, Denmark, Sweden,Holland, and Poland also deserveattention. It is impossible to sayjust which stations will be bestreceived in any particular place ; onecan only make suggestions on generallines.

Satisfactory MethodI am going to introduce to readers

a method which I have foundeminently satisfactory during severalpast summers, for ensuring goodlong-distance reception in the lightermonths. Begin by looking down thelist of foreign transmissions and selectfrom it twenty stations or so whichappear most promising.

The first point to look at is theposition of the stationand the power that ituses. You may find inyour district that recep-tion is generally bestfrom stations lying incertain directions. Insummer time the" blanketing " effect ofwoods, and of largeisolated trees, close tothe aerial is particularlymarked, for trees arethen full of sap andcovered with juicy leavesso that they form fairlyeffective collectors ofwireless impulses.

In my own case, Iknow that stations lyingbetween due north andnorth-north-east, areof very little use insummer time. They areeffectively blanketed bybig trees and recordsshow the same story, summer aftersummer : transmissions from thesedirections have grown fainter withthe coming of spring and the rise ofthe sap.

Good and Bad DirectionsExperiment will soon show

whether in the case of any readerthere are good and bad summerdirections.

Let your preliminary list containonly stations of two kilowatts ormore. Leave the smaller fry alonefor the moment. Do not select any

station whose wavelength is so closeto its neighbours on either side thatis is certain to be heterodyned. Todo so is clearly a waste of time.Having made out your list, tune inthe stations one after another andmake a note of the strength andquality in each case.

Some you will find quite satis-factory, though others will have to beweeded out. You will also discoverthat some of them are quite goodbefore, say, g p.m., whilst othersmust be classed as late stations.

And now for a trip in summer -timeD.X. work, which will be foundextraordinarily useful : Don't neglectthe stations below 30o metres. Withthese the power used is not of sogreat importance as with those onhigher wavelengths. 'The shorter

Stanley Peters New Picture House, Edinbur hWho Broadcasts from the

g

waves have a wonderful way ofspanning distance in summer time.

From 30o metres right down to200, or below, there are numbers offine stations such as Cologne, Bor-deaux, Malmoe, Toulouse PTT, Kiel,Muenster, Nuremburg, and Stettin,whose quality and strength are oftenremarkable. Curiously enough, thelittle Swedish relays, whose power isonly from .25 to .5 kilowatt, are wellheard in many places right throughthe summer season.

On the long waves, the list ofpossibilities is a long one, for high

18

power and a high wavelength seemto make for good daylight ranges.The long waves would, in fact, beideal for summer reception were itnot for one unpleasant and importantfactor-the atmospheric.

Atmospheric TroublesThe higher the wavelength to

which a receiving set is tuned, themore violent as a rule is the inter-ference caused, when atmosphericsare about. The long -wave stationswill, therefore, be available only onevenings when the ether is `` all clear."This brings one to another useful tip.

On " atmosphericky evenings, ifstations above i,000 metres are bad,drop down to the upper half of thebroadcast band. Should you findthat there is no atmospheric inter-

ference here, conditionswill probably be betterstill below 300 metres.You will see, if youthink for a moment,how this helps the long-distance man. He wantsperhaps, to receive aspecial programme fromBerlin during the even-ing.

Having tried Koenigs-wusterhausen and foundatmospheric interferenceprevalent, he drops downto 484.6 metres and seeshow Witzleben is sendingout the programme. Henotices that there is lessatmospheric interfer-ence, but there is still toomuch to be quite plea-sant. He, therefore, putsa still smaller set of coilsinto the set and tunes inStettin on 236.7 metres,

with complete comfort. Never forgetthe relays of the various Continentalstations. If one wavelength will notdo, there is often another that willbring in the same programmeexcellently.

List of Reliable StationsAfter a few evenings of trying -out

possible stations, a fair copy list ofthe most reliable can be made. It willpossibly contain some stations oflower power than those mentioned,for in some localities certain of thesemay come through exceedingly well.


By R. W. HallowsIt will in any case, save a great

deal of trouble, since it enables oneto know just what stations are bestworth trying for when it is desiredto hear distant transmissions.

A further word about atmospherics.No means of getting rid of thementirely has yet been discovered.One can, however, do a good deal topalliate their effects. The moreefficient the aerial the better it is as acollector not only of signals that wedo want, but also of the crashes thatwe don't !

Using An Indoor AerialIn summer time, therefore, it often

pays, instead of the outdoor wire, touse an aerial suspended close to theceiling of a living -room. Again,atmospherics often come moststrongly from a certain direction forthey may be caused by a thunder-storm which is raging in some placeor other. The frame aerial, therefore,with its strongly directional proper-ties, may be of considerable assist-ance in minimising their effects.

On the Very Short WavesSo far, we have spoken only of the

medium and long waves. One of thegreatest joys in summer time isD.X. reception upon the very shortwaves. Far from being at theirWorst, many short-wave stationsare at their best during the summermonths. During the whole of lastsummer I never once failed to obtainexcellent reception of broadcastingfrom America when I wanted todo so.

The Schenectady station, 2XAD,which works on 21.96 metres, is not,as a rule, of very much use in winter-time, unless he is transmitting earlyin the evening. In the neighbour-hood of 20 metres signal strength isgreatest and fading least pronouncedwhen it. is daylight at either thetransmitting or the receiving end.

Schenectady's StrengthAt Is p.m. when 2XAD switches

on, it is only 7 o'clock in the eveningin Schenectady and, therefore, broaddaylight over there. Signal strengthis as a rule wonderful for the nextthree hours-and 2 a.m. is quite lateenough for most of us to sit up.

PCJ J, the Dutch station, comes through splendidly during summer

Here isan ideal set-ting fora goodportable set !

months as a rule, and there arestations in every part of the worldthat can be heard right through thesummer with the short-wave receiv-ing set.

If you do not already possess ashort -waver now is the time toacquire one. It is one of the mosteasily made of wireless sets, as youmay see by examining the designsthat appear at frequent intervals inthe WIRELESS IVIAGAZINE. Inexpen-sive too, for no high -frequencyamplification is needed.

Two -valuer SufficientAll, in fact, that is required in

order to hear short-wave stations,thousands of miles away is a grid -leak -and -condenser rectifying valvefollowed by a single note -magnifier.With two note -magnifiers in cascademany stations may be received uponthe loud -speaker. There is no diffi-culty whatever in operating a modernshort-wave set, and to do so is asheer delight. Don't forget, too, thatthe short-wave set makes an excellentbroadcast receiver.

All that is required to convert itfor work upon the longer waves is toprovide a suitable set of coils. If Iwere confined to a single receiving

' 19

Why notbuild the

ChummyFouror the Sun-shine Five?

set, I would choose, unhesitatingly, athree -valve short -waver with anextra set of coils suitable for thebroadcast wavelengths.

You will find your summer -timelong-distance work still more inter-esting if you keep a log and recordin it the dates and the times whenreception was at its best, making anote also of the state of the moon andof the weather as well as of barometerand thermometer readings.

Testing Some TheoriesBy going through the log at the

end of the season you can see whatconditions appear to make for thebest wireless reception on all wave-lengths and can judge whether thereis truth or not in the many theoriesabout weather and wireless that havebeen put forward from time to time.

DO NOT FORGET THATFULL-SIZE BLUEPRINTSOF ALL " WIRELESS MAG-AZINE " SETS FOR HALFPRICE IF USE IS MADEOF THE COUPON ON PAGE

iii OF THE COVER

Wireless Magazine. August. 1928rEMIN111.100 IMRE MMMMMMMMM Oa MMMMMM 0. MMMMMM MMMMMMMMMMM 111111

Although a good four -valuer will do almost everything that is required for normal use thereis a need for a really " super" broadcast receiver, and details of the Connoisseur's Six, whichis completely described in this article, are published at the request of a large number ofreaders particularly those who reside overseas in distant places. All the parts are standard

and can be obtained without difficulty

LAST TWO VALVES" PUSH -PULLED "

FOR PURITY

SIX OR THREEVALVES AT WILLBY MEANS OFSINGLE SWITCH

SWITCH FORGRAMOPHONE

PICK-UP

SIMPLE AND EFFEC-TIVE VOLUME

CONTROL

6nnoisse12rs% JCX

Plan view of the baseboard of the Connoisseur's Six

FROMmany quarters we have received requests for a

" super " broadcast set, incorporating every possiblerefinement, and capable of " delivering the goods "-aset, in fact, that is quite definitely the best possible inevery way.

Many Weeks Spent in Perfecting DesignThus the Connoisseur's Six saw the liglit of day after

many weeks had been spent on its perfection by theWIRELESS MAGAZINETechnical Staff. Thegeneral points of thedesign will appeal to alarge number of readers,even though they donot desire such a power-ful combination them-selves.

In the first place,however, it should bepointed out thatalthough six valves areemployed, there areactually only five stagesof amplification, the lasttwo valves beingarranged on the push-pull system, so that ordinarysuper -power valves will give "super -super -power" results,without the need for an impracticable high-tensionvoltage.

Essentially the Connoisseur's Six comprises two stagesof high -frequency amplification, a detector, a resistance -coupled low -frequency stage and a push-pull transformer -coupled stage (two valves). The set is arranged for gramo -radio by incorporating two terminals to which a pick-upis permanently connected ; it is brought into circuit by theoperation of a simple push-pull switch.

20

Wiring and components on under side of baseboard of Connoisseur's Six

COMBINEDSURFACE AND

SUB -BASEBOARDWIRING

ANODE -BENDDETECTOR WITHPOTENTIOMETER

SEPARATEHIGH TENSION FOREACH VALVE GROUP

DESIGNED BY THE" W.M. " TECHNICAL

STAFF

Further details of the circuit are that the high -frequency stages make use of standard binoculartransformers, neutralisation being carried out on thesplit -primary principle. The detector works on the anode -bend principle, while the first resistance -coupled low-frequency stage is provided with a " motor -boat"stopper.

" Push -pulling" of the final valves is carried out byplacing two resistances in series across the secondary

of the low -frequencytransformer and tap-ping off from the mid-point. This system hasbeen found by the WIRE-LESS MAGAZINE Tech-nical Staff to be par-ticularly successful. Aspecial output trans-former with a centre -tapped primary is, how-ever, employed.

For the convenienceof those who desire tolisten only to the localstation, a switch is pro-vided for transferring

the aerial connection from the grid of the first high -frequency valve to the grid of the detector valve, at thesame time switching off the filaments of the two high -frequency valves.

Controls for Every Purpose for Best ResultsIn keeping with the de -luxe nature of the Connoisseur's

Six there are a large number of controls. The two smallknobs at the top of the panel are the detector anode -bendpotentiometer and master rheostat respectively. Acrossthe centre of the panel are three large dials attached

to the condensers for tuning the aerialand two anode circuits.

Between these, on a lower level, aretwo smaller dials for the reaction con-denser and volume control, whichtakes the form of a variable leak in thegrid circuit of the first low -frequencyamplifying valve.

Three Panel SwitchesIn line along the bottom of the

panel a -e the push-pull switch forputting the gramophone pick-up incircuit, the key switch for cutting outthe two high -frequency valves and themain on -off push-pull switch.

As well as these controls on the frontof the receiver, there are two neutral-ising condensers for the high -frequency


o wuris nruvu

3/00,1.

0005

°NA° 1=

G15- ca -a

011T+4

0117+351+2

0171,4

NT -

LT

LT+%Mr!.

Circuit of the Connoisseur's Six with the last two valves "push -pulled"

stages on the baseboard and a tapped grid -bias batteryworking in conjunction with the anode -bend potentio-meter for the detector.

At the back of the receiver are provided no less thansixteen terminals, arranged as follows : Aerial, earth,pick-up (z), low-tension -I- and -, high-tension positivesfor the high -frequency stages, detector, first low -frequency and final stages (4) and negative, grid -biasnegatives for first low -fre-quency and final stages (2)and positive, and loud -speakerterminals.

Special WiringYet another special point

about the Connoisseur's Six isthe combination of surfaceand sub -baseboard wiring,which gives a remarkably neatappearance to the finishedreceiver and also saves timein construction.

Except that it does incorporate a large number ofrefinements not found, and indeed not required, in theaverage broadcast receiver, we desire to emphasise thefact that the Connoisseur's Six is quite straightforward indesign, and makes use of standard parts that should beobtained from dealers everywhere without difficulty.

Though all the essential details regarding this set areincluded in these pages, and we have no desire to forcereaders to work from a blueprint, yet this course will

save a great deal of time and trouble, notwithstandingthe fact that the constructor may be well experienced inradio matters.

If the original specification is followed (and it isparticularly desirable that it should be) the blueprintacts as a full-size drilling template for the panel layoutand complete wiring diagram with the most con-venient sequence of wiring indicated. Moreover, up

to the end of August thisar

-I." 3

46. - 144

3A5 4156

Panel layout of the Connoisseur's Six

Front view of the Connoisseur's Six showing arrangement of controls

21

blueprint, which measures2o in. by 3o in. can beobtained for half-price, thatis 9d. post free, if a postalorder for that amount is sentaccompanied by the couponat the bottom of page iii ofthe cover.

Where to SendAsk for blueprint No. WM

88, and address your inquiryto Blueprint Dept., WIRELESS MAGAZINE, 58/61 FetterLane, E.C.4, before August 31 if you want the blueprintat half-price.

It is advisable in assembling a set of this type not tobegin the construction at all until all the parts have beenobtained. But when everything is ready, the panelcomponents can be mounted in position. These includethe master rheostat and potentiometer at the top, thethree large tuning condensers, the reaction condenserand variable grid leak, and the three switches at the

bottom.The baseboard itself is provided with a strip

support at each end and the front edge of the base-board is screwed to the panel 2 in. from thebottom edge of the latter, no brackets beingemployed.

Arrangement of Baseboard ComponentsThere is little difficulty in arranging the base-

board components. The three six -pin coil basesand the two neutralising condensers for the high -frequency valves are arranged in. line. At theleft of the baseboard, looking from the back of thereceiver, are the low -frequency transformer, withthe two .5-megohm grid leaks in series across itssecondary, and the output transformer.

Underneath the baseboard are the low -frequency

coupling condensers, the anode resistance and the"motor -boat" stopper. The arrangementparts is clearfrom the photo-graphs and blue-print (or thesmaller layoutand wiring dia-gram, repro-duced on page24)

Wiring up theset will be verygreatly facilit-ated (even if theconstructor canwork from a cir-cuit diagram !)if the full-sizeblueprint is used.This not onlyindicates clearlywhich points arewired together,but the most convenient sequence is also clearly shown.

As soon as all the parts have been firmly fixed, placethe receiver with the panel farthest from you andpick out on the wiring diagram those pointsmarked a. Some of these will be above the base-board and others on the under side. First wiretogether those points which are above the base-board and drill holes at the points indicated forthe sub -baseboard wires.


The Connoisseur's Six (Continued)

The Con-noisseur'sSix withValvesand bi-no.cularcoils inposition

Before testing the set, suitable valves and coilsmust be obtained. There is considerable latitude inthe case of the former, but no difficulty at all aboutthe latter. The coils used are Lewcos six -pinbinocular transformers, of the split -primary type.These are made in two ranges, one for the bandbetween 250 and 55o metres and the other for ther,000 to 2,000 metre waveband.

Choosing Suitable Valves for the ReceiverFor the high -frequency stages, two valves with

impedances in the neighbourhood of 20,000 to30,000 ohms will be suitable, while for the detectorstage (which is resistance -coupled to the first low -

Note the neat appearance frequency valve) a valve with an impedance inresulting from the combina- the neighbourhood of 6o,oco to 8o,000 ohms will betion of surface and sub- best; considerable latitude is, however, permissible

baseboard wiring in this case.If a valve with an impedance of the order of r5o,000

of all ohms is used an anode resistance of .5 megohm should beused in place of

these

VALVES TO USE IN THE CONNOISSEUR'S SIX

Make. H.F.Amplifiers. Detector. 1st. L.F.

Amplifier.Push-pull

Valves.

Cosmos ... ... DE5o SP5oB SP5oR SP5oR

Cossor ... ... 6roHF 6roRC 6IoLF 61oP

Ediswan ... ES5HF RC6ro ES5LF PV6i 0

Marconi ... DEH6to DEH62o DEL6 to DEF6to

Mullard ... ... PM5X PM5B PM6 FM256

Osram ... ... DEH62o DEH62o DEL610 DEP6to

Six -Sixty SS6o75HF SS6075RC SS6loP SS625SP

Equivalent 2 -volt and 4 -volt valves can, of course, be used.....

Wiring on the Under Side of the BaseboardNow push through all the a holes wires which

will project through to the under side of the base-board. Turn the set over and join together all thea points on the under side of the baseboard in themost convenient way.

When all the a points have been thus wired,connect up the b points in the same way, and carryon throughout the alphabet. After the pointsmarked z go on with aa, bb, etc.

the .25-megohmresistancespecified.

The first low -frequency ampli-fier should havea much lowerimpedance,since it is trans-former -coupledto the final stage ;an impedanceround about15,000 ohms willbe quite good.

For the finalpush-pull stagetwo super -powervalves of iden-tical characteris-tics should be

used. These can have an impedance of anything below6,000 ohms. Using two super -power valves in " push-pull"

22

TheConnoisseur'sSix withoutvalves or coils

The three holders for the six -pincoils and the two neutralisingcondensers are arranged in lineat the right of the baseboard


A " Super" Set for the Discriminating Listenergives double the grid swing of either of thevalves on its own; thus it is possible to get whatmay be termed " LS5A results" without the needfor what in many cases is an impracticable high-tension voltage.

Testing Out the Connoisseur's SixTo test out the Connoisseur's Six, insert the

required valves and coils in their respectiveholders and connect up the various batteries.

Normally the grid -bias battery for the detectorvalve, (mounted on the under side of the base-board), which works in conjunction with the anode -bend potentiometer should be tapped off at theI1/2 -volt point and the potentiometer used forvarying the actual voltage applied to the grid.

To H.T.-1- (which supplies the anodes of thetwo high -frequencyamplifying valves) Another view of theapply 6o to 8o volts Connoisseur's Sixpositive; to H.T.d-z

supplies thedetector) a higher volt-age can be applied asthe valve has a muchhigher impedance andthere is also a highresistance in its anodecircuit-say 90 or ioovolts.

Normally the fullvoltage of the battery,which should be at least To the extreme left is

120 volts, can be applied ttpecial output transformer,

andto both H.T. + 3 " ientteorvtahleve ransformerrightt of it is the

TheConnoisseur's

Six

A large number ofterminals is necessary so thatcritical voltages adjustments can bemade for the valve anodes and grids

COMPONENTS REQUIRED FOR-Ebonite panel, zo in. by 8 in. (Parfait,

Becol, or Raymond).3-.0005-microfar id variable condensers

(Burndept, Cyldon, or fgt. inic).3-Vernier dials (Flumdepl, Igranic, or

Formo).1-.00ca-microfarad reaction condenser

(Cyldon Bebe, Bulgin, or Igranic).t -7 -ohm panel rheostat (Lissen, Peerless,

or Igranic).1 -400 -ohm panel potentiometer (Lissen,

Igranic, or Bumdept).1-High-resistance potentiometer, 500,000

ohms (Dubilier or Igranic).2-Dial indicators (Bulgin).1-On-off push-pull switch (London and

Provincial, Lotus, or Lissen).1-Single-pole change -over push-pull

switch (Lotus, Lissen, or Bulgin).6 Anti-microphonic valve -holders (Lotus.

W. & B., or Ashley).3 -6 -pin coil bases (Lewcos or Cason).2-Baseboard neutralising condensers (Peto-

Scott, Bulgin, or Gambrel)).t -Low -frequency transformer, approxim-

ately 4 to t (Igranic type G, MarconiIdeal, or R.I. and Varley).

z-.5-megohm grid leaks with holders(Mullard, Dubilier, or Lissen).

1-Output transformer with centre -tappedprimary (R.I. & Varley).

THE CONNOISSEUR'S SIXI -Double -pole change -over key switch

(Wearite, Dubilier, or Burndept). 1-25o,000 ohm wire -wound resistance with

holder Dubilier, Mullard, or (R.I. &Varley).

1 -5o,000 -ohm wire -wound resistance withholder (Dubilier, Mullard, or R.I. &Varley).

1-2-m'crofarad fixed condenser (Dubilier,Hydra, or Lissen).

1-Horizontal high -frequency choke(C.D.M. or Cosmos).

I-.006-microfarad fixed condenser (Dubi-lier, Mullard, or Lissen).

1-.ol-microfarad fixed condenser (Dubi-lier, Mullard, or Lissen).

t-Flashlamp battery clip (Bulgin typeGBz).

1 -41 -volt grid -bias battery (Siemens,type GI, or Ever Ready).

t -Cabinet and baseboard, to in. deer:(Cameo).

1-2o in. by 2 in. terminal strip (Parfait,Becol, or Raymond).

t6-Terminals, marked : Aerial, Earth,Pick-up (2), L.T.+, L.T.-, H.T.-,H.T.± 1, H.T.-1- 2, H.T.+3, 1-1:rdi-

, G.B.-z, ,

L.S.- (Belling -Lee).2-Wander plugs (Lectro Linz)r yd. flex with spade tag.12 -2 -ft. lengths Glazite.

23

H.T. 4 (the forme,feeds the anode of thefirst low -frequencyvalve and the latter thefinal "push -pulled"valves.) When aneliminator is available,however, it may bepossible to apply 15ovolts, or more, to thelast two valves, in whichcase not more than 120volts should be suppliedto H.T.+3.

It is not so easy torecommend the amountof grid bias that willgive the best repro-duction, as so much

depends upon the actual valves used.Normally 6 to 9 volts negativeshould be applied to G.B. andprobably as much as 12 to 18 voltsnegative to G.B.-2.

H.T. Battery for Grid BiasIt is convenient to use a 36 -volt

high-tension battery for obtaininggrid bias for the Connoisseur's Six.,Remember that the more grid biasthat is applied the lower is the high-tension consumption, a point of someimportance when six valves are in use.

The degree of selectivity can bevaried by taking the aerial connectionto either terminal No. 3 or No. 4 ofthe aerial coil and both positionsshould be tried.

To tune the set, pull out the right-hand push-pull switch (which lightsall the valves) and see also that theknob of the left-hand switch is " out"(otherwise the gramophone pick-upwill be connected in circuit). The

rWireless Magazine. August. 1928

The Connoisseur's Six (Continued)

middle switch should bein the right-handposition for all six val-ves (left for three valvesonly).

ReactionAdjust the reaction

condenser until theslight rustling or hissingsound is heard from theloud -speaker, whichindicates that thereceiver is on the vergeof oscillation. Nowturn all three maintuning dials in unison,until a station is pickedup. (Note that rightround the scale thethree readings will bethe same within aboutone or two degreeseither way.)

As soon as a trans-mission is picked up,adjust the anode -bendpotentiometer and re-adjust the reaction con-trol until the best resultsare obtained. Finallyadjust the volumecontrol.

NeutralisationBefore the Connois-

seur's Six is put intogeneral use, however,there is another pointthat needs attention,and that is the neutral-isation of the high -frequency valves.

To do this remove onefilament connection ofthe first valve (havingfirst tuned -in a station)and adjust the firstneutralising condenseruntil signals become quite inaudible. Re -make the fila-ment connection and repeat exactly the same processwith the second valve.

If the valves are neutralised on the lower waveband itmay be necessary to re -neutralise for reception on theupper waveband and vice versa.

When the centre switch is in the left-hand position,only the detector and low -frequency amplifying stages

51111. arne---"

0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0G13-2 G5-1 GM nT.4 nit, iTry KT. t1 LT- LT* Rd -UP WOW MR.I.

This layout and wiring diagram of the Connoisseur's Six can beobtained as a full-size blueprint for half-price, that is, 9d. post free,if the coupon on page iii of the cover is used by the end of August.

Ask for No. W.M.88.

are in use, the filamentsof the two high -fre-quency being automat-ically switched off. Itis then only necessaryto tune the right-handcondenser dial, thesecondary of thesecond high -frequencytransformer in this casefunctioning as an aerialcoil.

No ScreeningFor the benefit of

novices in radio, it maybe pointed out thatbinocular coils have anegligible externalfield and, therefore, nometallic screening isrequired.

To operate the Con-noisseur's Six as agramo-radio amplifier,put the middle switchin the left-hand positionso that only three valvesare in circuit and pushin the knob of the left-hand switch, after hav-ing connected the pick-up to the two terminalsprovided at the back.

Volume ControlIn this case, the only

control that needs ad-justment is the variablegrid -leak for controllingvolume.

From this briefdescription it will berealised that the Con-noisseur's Six makes thebest possible use ofexisting componentsand can be relied uponto give really good re-

sults. It is difficult to estimate the range of such apowerful receiver, but it will be possible in most casesto rely upon the reception of fifteen or twenty stationsat loud -speaker strength every evening.

Because of its great power, the Connoisseur's Six isan ideal receiver for use during the summer months,when reception conditions are never ideal by anymeans.

More About the Chummy Four on Other Pages of this Issue!

24

Some New &'Interesting Disclosures byCAPT. H.DE A, DONI STHORPE


BY reason of the fact that broad-casting did not come into being

until after the Great War had beenfinished for some four years thereare many people who do not realisethe important part that wirelessplayed in everyday life prior to theinception of this wonderful newform of entertainment.

A Broadcast fromNewcastle

Recently I was giving a specialbroadcast from the Newcastle broad-casting station entitled "Wirelessand the War" and since that talk Ihave been asked by a number of mylisteners, who were associated withme during the war, to give thecontents of this talk in story form.What better medium is there, there-fore, than the WIRELESS MAGAZINEto disseminate these wireless warstories?

I do not think it is generally knownthat the thermionic valve, which isused so univer: 11: to -day for mag-nifying and detecting signals comingfrom broadcasting stations, came intocommercial use round about thetime when the Great War started.

Recognising the Valueof the Value

Coinciding, therefore, with thebeginning of the war, the Britishofficials quickly realised the value ofvalves for detecting and magnifyingwireless signals coming from longdistances, and stations were erectedimmediately the war started invarious parts of the country forintercepting messages from enemywireless stations.

It was my honour, with two otherofficers, during December 1919, tointroduce the thermionic valve tothe British Expeditionary Force in

In this article the WIRELESS MAGA-ZINE is able to give its readers anew insight into the part thatwireless played in our lives longbefore broadcasting was inaugu-rated, or even thought of. Theauthor was one of the officers whointroduced the valve to our forcesin France in 1919 for the first time

-only nine years ago !

France. In France, prior to thatdate, the listening -in for enemymessages by the British WirelessSignal Corps was accomplished bymeans of crystal receivers only, andthe competition between the BritishWireless Corps and the French Wire-less Corps in this direction was verykeen, and each day the messagesintercepted by the two armies werepooled together, and deciphered at acentral headquarters, with the resultthat much valuable information wasobtained therefrom.

Astonishing IncreaseImmediately we introduced the

thermionic valve into the wirelesssets of the British listening stationsthe number of messages which wewere able to intercept over theFrench increased astonishingly, andthe information so obtained becameextraordinarily valuable, because sig-nals were picked up from Germanyarmy stations located at a consider-able distance away from the front.

This fact caused much consterna-tion amongst the Frenchmen, whocould not realise at once why we weredoing so much better in this directionthan themselves, and they, therefore,asked whether they might be allowedto come over and inspect our specialreceiving apparatus.

I remember very well the day thatthe French inipecting officer enteredmy wireless cabin. If e just took onelook at my valve and said.: " Ah !

25

That is the secret, it is the little lampthat is giving you the advantageover us," and from that day theFrench army also introduced thethermionic valve into their wirelessreceivers.

As a matter of fact wirelessmessages from the German fieldstations were often received anddeciphered by the Allied Armiesbefore the German station to whichthey were addressed had properlyreceived them.

Interesting WorkOne of the most interesting parts

of the work carried out by the wire-less signals during the war was thatof direction -finding. By means of aseries of wireless direction -findingstations, it was possible for us tolocate the positions of German wire-less stations.

A wireless direction -finding appa-ratus is an instrument capable ofdetecting the direction from whichwireless signals originate, so that ifyou have two or three of these sta-tions on a base line it is actuallypossible to locate the exact positionwhence the signals are coming.You will readily appreciate thevalue of this work as far as war isconcerned.

Listening for the GermanFleet

In England on the east coast therewere a number of these stations,whose sole work it was to watch themovements of the German fleet.Every time a German battleship,submarine, or destroyer sent out awireless message, these signals wereimmediately picked up by all thesedirection -finding stations and theirposition was plotted out on a largechart at the Admiralty, as was

Wireless Magazine, August, 192j

How Wireless Helped to Win the War ! (Continued)

intimated by Sir Alfred Ewing in hisrecent Press disclosures.

I do not think it is generally knownthat this direction -finding apparatuswas to a large extent responsiblefor the great battle of Jutland.

The Zeppelins when they maderaids on England also used theirwireless to a great extent, and hereagain our wireless direction -findingstations were exceedingly useful forplotting out their journeys across theNorth Sea. As a general rule, how-ever, as soon as they crossed thecoast -line they ceased utilising theirwireless, no doubt app:eciat:ng thefact that they were being watched byour wireless stations.

A Zeppelin RaidOn one particular occasion, how-

ever, I remember rather an interest-ing story in connection with one ofour direction -finding stations, locatedin the Midlands. A Zeppelin raidwas taking place and one particularZeppelin was using its wirelessconsiderably-all its messages beingintercepted by this particular direc-tion -finding station, and its directionfrom that station was periodicallynoted.

At one particular stage of thisZeppelin's journey, however, theoperator at the direction -findingstation became considerably alarmedby reason of the fact that his wirelessdirection -finding apparatus wouldshow no direction whatsoever as towhere the Zeppelin was. He couldnot understand this for the moment,and then it suddenly dawned on himthat since there was no direction theZeppelin must be directly overhead.

Directly Overhead!He rushed out of his wireless

cabin, and sure enough there wasthe big airship almost directly over-htad with its engines purring away.

Another interesting story aboutthe wireless war which 1 did notrelate on the " ether " is oneconcerning the East.

A certain station was erected bythe British Army on the easternfront for the transmission of wirelessmessages and for the interception ofenemy messages. This station hadan aerial supported from an enormousmast, and as soon as this station waserected it immediately performed

most useful work, and was of greatvalue to the service.

Unfortunately this mast laydirectly in the path between Jerusa-lem and Mecca. Here lay thedifficulty !

Shortly after operations h a dstarted an officer from general head-quarters arrived one day togetherwith one of the eastern potentatesand informed the wireless officer -in -charge that the site would have to bealtered forthwith as the mast, in viewof its location, was offensive to thelocal natives' religious susceptibilities.

The station was changed at once,

LIONEL TERTIS, THE 'WORLD-FAMOUS VIOLA PLAYER

and the mast with considerabledifficulty was dismantled and re -erected only a few hundred yardsaway which satisfied, politically, thoseon whose ground we were fighting.

In conclusion I would like to tellyou an amusing story regarding ahoax which was played on the wire-less section of the British Army, by acertain sergeant. This sergeant cameto the wireless headquarters and saidthat he had invented a new wirelessapparatus which made use of somehitherto unknown ray. He said thatby means of his apparatus it waspossible for him to take pictures ofand locate pieces of shell embeddedin wounded soldiers.

He was asked to demonstrate hisapparatus, and was taken to one of

26

the military hospitals, where we put,his apparatus to test. It is reportedthat his apparatus consisted of arevolving cylinder with a needlemoving across it after the fashion ofthe old phonograph. The mani-pulation of the apparatus was accom-panied by the crackling of spr.rks.He took several photographs with hisapparatus of wounded soldiers andlocated the positions of pieces of shell,:and these photographs when deve-loped were remarkably clear, andapparently helped the surgeons intheir operations for removing thesepieces of shell.

Extravagant ClaimsElated by his success, however,

his claims became rather extravagantin that he said his apparatus was sopotent that the rays from it wouldkill a rabbit if they were directed onthis unfortunate animal although afew yards away. He demonstratedthis effect and somewhat aroused thesuspicions of his spectators. Therabbit, therefore, was taken awayafterwards, unknown to the sergeant,and it was found that the unfor-tunate animal had been poisoned.

It was, therefore, necessary for hiswhole apparatus to be thoroughlyinvestigated. This was difficult to dowithout arousing his suspicions. How-ever, eventually, but not until aftersix weeks had elapsed, it wasdiscovered that in spite of the factthat most of the wires of his apparatushad been substituted by pieces ofstring, unknown to the sergeant, heproduced the results just the same.

Fooling the Army!It was then found that the photo-

graphs which he had been producingwere actually pictures drawn out byhim on a sensitive plate by means ofa piece of chemical in the dark room,where hitherto nobody except him-self had been allowed to enter. Hewas a wonderful draughtsman, andhad a good knowledge of anatomy,and had so fooled the medicaland wireless sections of the army.As a reward for his little hoax he wasgiven eighteen months hard labour.

Some time afterwards an officer inthe War Office, with a towel round hishead, endeavoured to explain in anofficial report how it was it had takensix weeks to detect this hoax.

Wireless Magazine, August. 1928_1

Valve Soot:WhatjtjsVERY close examination of valves

which prove to be gettingdefective will often disclose, when,held up to a strong light, smallquantities of black, fine, powder-soot-the " mystery, " to mostpeople, is concerning where thiscarbon deposit comes from.

Fig. I.- Greatly magnified view of thevalve mirror (inside), showing itssemi-crystaline structure. It consists

of sub -limed magnesium

This substance commonly arisesonly from the combustion of organicmatter-for example : coals, paper,wood, cloth, and so on. The metalfilament, and the bulb glass, areinorganic!

Now valve soot issues from glass -gas mainly, and partly from metal -gas, and water vapour, which can bereadily demonstrated in thelaboratory.

Liable to DeteriorationWhen ,high -quality valves are in

good working order, and are carefullytended, their efficiency is remarkable ;but on account of this high degreeof superiority they are liable todeteriorate under influences whichare not popularly known.

Whether the valve is filled withinert gas, or any other kind, or ismerely a vacuum, minute leaks maypermit the entrance of air; so alsomay water vapour pass.

The gas concerned with the troublein question is known as carbon -dioxide, carbonic anhydride, car-bonic acid gas, and CO2. It isabsolutely invisible; yet soot can

be chemically precipitated from it.A similar procedure follows within

a valve. The filament gets over-heated, or otherwise affected, withthe result that the oxygen of theinvisible gas inside the bulb isgradually absorbed by it, and partlycorrodes the wire. The carbonelement of the gas, having thus beendeprived of its oxygen companion,falls down as fine-grained soot.

" Silvered " ValvesMany valves have their glasses so

completely " silvered " that the in-terior can hardly be seen ; yet whenthey are carefully examined, thetiny black specks can be seen, andmay be shifted about like a pinchof dust.

It represents a loss of energy inthe current which only the mostdelicate instruments can measure;yet it accounts for faults in receptionwhich often puzzle the listener !

Researches are stilllreingconductedinto the amazing compound knownas "glass -gas," consisting of carbon -dioxide and water -vapour deliveredfrom the air. Valve -glass has actuallybeen proved to be ultra -minutelyporous-panes, in a similar sense,

Fig. 2. Greatly magnified view ofvalve wire with globules of condensedwater vapour thereon. As the wirecools, and is subsequently electronised,

these items appear and disappear

transmit daylight. Mr. Clifford C.Paterson, Director of the ResearchLaboratories of The General ElectricCompany, Ltd., Wembley, said in an

address before The Royal Society ofArts, on February 16, 1927 :

The word "occluded" is used tocover this latter state, the precisenature of which is not very wellunderstood.But we can see the results, partly

explained in the diagrams. The air,

Fig. 3.-Greatly magnified view ofvalve soot, precipitated from carbon -dioxide, derived from ".glass -gas,"and " metal -gas," water vapour, etc.

etc., passes in between the palerareas shown in Fig. 1; settles on thefilament as shown in Fig. 2 ; and hasits soot (carbon) isolated from it asshown in Fig. 3. JAMES SCOTT.

LA POLITESSE !HOWLING to show disapproval

of a certain broadcast item isthe latest form of radio bad manners.If the howling were vocal, and con-fined to the home, well and good :but when it comes to radio howling,and done in the middle of somethingof which the oscillator does notapprove, well, I ask you. .

A Certain CureThere is nothing much which

virtuous listeners can do to preventthis, but if anybody knows a friendor a neighbour who makes a habitof " booing " at radio artistes in thismanner, here is an appeal to stophim at it.

Phoning the B.B.C. to say " Pleaseshut it off," is better for all otherlisteners-and just as effective.

A. B. B.

If You Want A Portable Set For Your Sidecar Turn To Page 49727


You Will Not Be Getting the Best Out of Your Set Until You Knowy

impic _e erg Can _e2owYouDo you realise that by using meters in a set you notonly get better adjustments and better results, butactually save money by being able to check the con-sumption from your batteries? On the left is aphoto-graph of a motor -car set equipped with no less thannine different meters. This article explains their uses

THE facia -board equipment ofmost modern cars includes a

clock, speedometer, ammeter andoil -pressure gauge. None of theseinstruments is really essential, ofcourse, but there are few drivers whowould not feel uneasy if they couldnot obtain at a glance the informa-tion that the dials give concerningthe running of the engine and soforth.

Meters are Handy AdjunctsAlthough only infrequently does

one come across a wireless set solavishly equipped with instrumentsof all kinds as are the majority of carfacia -boards, there are many reasonswhy voltmeters, ammeters and milli -ammeters are handy adjuncts of awireless set.

The most obvious reason, too, isthat it is possible to tell what ishappening in very many receiversonly by what comes out ofloud -speaker. It does notfollow that the volume orpurity of reproduction isan accurate guide to howa set is working, evenwhen the reproductionseems quite good.

Hard to TraceMatters are even worse

when reproduction is notquite good, for then thecause of poor signalstrength, distortion, orwhatever it may be, isdoubly hard to trace ifloud -speaker output is theonly guide available.

The type of measuringinstruments which are

the

useful accessories to an ordinaryreceiver are not necessarilyexpensive. Neither are they

only suitable for bulgy-browedexperimenters, or for use in labora-tory sets. There is room in mostbroadcast receivers for at least twoinstruments, and there are, in thewriter's opinion, few receivers thatwould not give better results owing tothe accurate indication given ofwhat is going on " inside."

Perhaps that may seem rather abig claim to make, but it is not so far-fetched as some of the hit-and-missmethods which many use to " test"their sets and to track down troubles.

A Concrete CaseAs an instance, let us take a

concrete case. A three-valver, shallwe say, incorporating two stages ofL.F. amplification, suddenly refusesto work as it should. Volume isreduced a little, and there is quitenoticeable distortion. The set is,nevertheless, quite sensitive andpulls in the distant stations in the

normal manner expected of it."Ah," the Wise Man will say,

" there must be some little fault inthe L.F. part of the set, the detectorbeing O.K." The question then is :In which part of the amplifier isthere a fault?

Cutting Out a ValveThe loud -speaker is disconnected

from its normal output terminalsand put in place of the primary of thelast transformer, so cutting out thethird valve. Distortion is still notice-able and strength is not up to normal.,

"Ah," says the Wise Man again," then the fault must be in the firstlow -frequency stage." A pair ofphones is substituted for the primaryof the first transformer, bringingonly the detector into use. There isno distortion, and in every way thedetector appears to be functioningcorrectly. The fault, therefore, is inthe L.F. side, which is what wassuspected at first, and the elimination" test " has done nothing but wastetime and confuse.

This diagram gives some idea of what a three-valver wouldbe like were it equipped with every possible meter

28

Possible FaultsThereafter, without

proper measuringinstruments, the unluckyset -owner is working inthe dark to trace themysterious trouble. High -and low-tension voltagesmay be incorrect (theH.T. battery or accumu-lator having become dis-charged) , one of thevalves may have lost itsemission, and many simi-lar faults may be presentwhich are most difficultto track down withoutammeters, milliammetersand voltmeters.

There is no prize for guessing thecause of the distortion and loss ofvolume in the receiver cited in theforegoing example !

Increase of ResistanceThe whole trouble was due to a

slight accidental increase in theresistance of the master filamentrheostat. Low-tension current wasreduced, causing distortion in theL.F. stages, but not affecting detectorsensitivity in any way. The faultcould have been located in a fewminutes with a low -range voltmeterplaced across each set of filamentlegs in turn.

A good high -range voltmeter read-ing up to about 12o volts (and by agood voltmeter is meant one whichrequires a minimum of current forfull-scale deflection) would be apositive assurance that the H.T.battery was not run down.

ILLIAMPERE

A milliammeter placed in the finaloutput circuit is a check on high-tension current consumption and

also detects distortion

Moreover, it would have shownthat each section of the battery wasin order, and that the voltage atboth first-L.F. and detector tappingswas approximately what it should be.

A milliammeter placed in turn inthe anode circuit of each valve wouldshow whether or not the emissionwas satisfactory, and without muchdifficulty would show if distortionwas being produced in first or secondlow -frequency stages, or both.

Indicating DistortionWhen the receiver was once more

working satisfactorily the milliam-meter could occasionally be placed inthe anode circuit of the power valve,in series with the loud -speaker, toindicate if distortion is occurring.Tests might also be made with high-tension and grid -bias voltages in anattempt to cut down the steadyH.T. current without affecting purityof reproduction.

rele-ss Magazine, August. 1928

When a milliammeter is placed inthe anode circuit of a valve, distortionwhich is produced in that valve (bythe grid signal voltages swinging overon to the top and bottom curvedparts of the characteristic) can beseen, and often it is possible to checkvery slight distortion which is shownby the milliammeter and yet whichis not noticeable to the ear.

A valve working properly on thestraight part of its curve gives apractically steady milliammeter read-ing. Swing -over on to the top orbottom curves, and consequent dis-tortion, will cause the milliammeterto show a large deflection from itsnormal reading. This is a positivetest.

It is not suggested that valve -setowners should go to the expense ofpurchasing instruments of laboratoryaccuracy, nor when good instrumentsare obtained need they be per-manently incorporated in a set.

Dual-purpose MetersDual-purpose ammeters and volt-

meters are to be obtained : forexample, a meter to read both high -and low-tension voltages, or to showhigh-tension voltage and currentmay be purchased, and saves thecost of two distinct instruments fortwo distinct purposes.

Tapping points should be providedin the set so that the flexible leadsfrom the meters may conveniently beplaced in circuit. In the anodecircuit of each valve, for instance,there should be two small terminalsmounted on an ebonite strip, eachpair being ordinarily connected bymetal straps.When there isreason to suspectdistortion thestraps may beremoved and themilliammeterplaced in turn oneach pair of term-inals, the needledeflection beingnoted.

Perhaps thebes-t way tobecome convincedof the real needfor accurate elec-trical measuringinstruments is to purchase a full set-milliameter and high- and low -volt-age meters. The frequency withwhich your wireless neighbours willwant to borrow one or the other of

29

A simpler type ofdouble -scalevoltmeter, whichcan easily be car-ried in the

pocket

the set will more than eonvitums you IAnd now, just a word as to the

construction of the instruments them-selves, and to the points for whichpurchasers should be on the look -out.

Most amateurs will be aware that

This is a double -scale voltmeterwhich can be used for checkinglow-tension and high-tension

voltages

voltage measures of all kinds have ashigh a useful resistance as possible,this being obtained by winding ona large number of turns of wire.Current measurers, however, nomatter whether ammeters or measur-ers of milliamps, must have as low aresistance as possible, for meters ofthis kind are placed in series with thecircuit to be tested. Any undueresistance in the meter itself wouldupset conditions and cause a falsereading to be obtained.

High -resistance VoltmetersCheaply -made voltmeters, say for

testing H.T. values, will give a falsereading if there is insufficient wire onthe armature or field. The resistance

of the meter willbe such as tocause appreciablecurrent flow fromthe battery whichis being tested.The load will beabove the normal,and a false read-ing will be given.A good voltmetershould consumethe minimum ofcurrent for full-scale deflection.Similarly, am-meters and othercurrent measurers

should have as low an internalresistance as possible. With thesepoints to guide him, the readersllould have no difficulty in choos-ing a reliable instrument. QUEUE.


Continental StudiosAn interesting article by BERNARDNE WM A N, the Leicestershirehumorist, who has broadcast from manyof the principal Western European

stations

THERE is a school of thought, Ibelieve, which holds that even an

inanimate object creates its ownatmosphere. I am quite ready tosubscribe to this doctrine so far asbroadcasting studios are concerned;the identification of studios by theiratmospheres would be no impossibletask.

Those atmospheres are influencedby two principal contributories-themere furnishings and decorations, andthe personality, of the studio staff.

Littte to LearnThe B.B.C. has little to learn from

Continental radio organisations inrespect to wireless technicalities, onthe contrary, the Continent can-anddoes-learn a good deal from theB.B.C. We are primarily a practicalnation ; most Continental races areprimarily intellectual.

So it is not surprising to find that,whilefollowing us in technical develop -ments, they lead us in many psycho-logical details. The detail in whichI am particularly concerned is themental comfort of the performer.

The London studios represent thelast word in manipulative efficiency-but their effect upon a sensitivemind is appalling. One's own per-sonality is quite lost in the purelyneutral surroundings. Thick carpetscover the floor; the walls are com-pletely hung with heavy curtains,maybe the roof is padded. All thisis to eliminate reverberation-a veryessential precaution.

Prevailing Deadly GloomBut the colour scheme is deadly

in its gloom. I cannot recall theshades-so confused is the effect-but there is a medley of fawns andgreys and drabs-an unreal mixtureof all that is damping to the spirits.The colour atmosphere is that of asombre vault; even the microphoneitself is camouflaged to suit its drearysurroundings.

The pla ce i s as unreal as the drawing -

room set used by an amateur dramaticsociety; the atmosphere is that of acertain non -calorific frigidity.

I have met this atmosphere ofdepression at no Continental station.One difference alone suffices forexplanation-colour. Abroad, true,they have theircarpets and curtains-but pleasing and enlivening shadeseverywhere present an entirelyalteredaspect.

Primary colours are a little start-ling at first to the English eye-butthe start is a vigorous impulse, not adepressing droop. Soon the atmos-phere tells; I recall the greens andreds of Cologne, where the principalstudio is an artistic delight.

BILLY MAYERL, OFSYNCOPATION FAME

I remember noticing at a Parisstation that even the music stands forthe orchestra were painted a vividscarlet. I do not suggest suchextremes for England. But who canoverestimate the influence of colour?Who would not rather fight among thegreen hills of Champagne than thebrown plains of Flanders? And whynot changeable colour schemes, tomatch the type of piece being broad-cast?

I have said, too, that the atmos-phere of the studio is affected by thepersonality of its staff. In Londonthe artist is greeted with a politeness

30

:: How They Put theBroadcast Artist

At His Easewhich is unfailing, but which isimpenetrable. People move about ina detached manner of aweing silence;even the mechanicians perform theirtask with a grim efficiency that isdisconcerting.

The artist feels that he cannot " getunder the skin " of the organisation.Everything is so impersonal.

Compare this with the frankeffusion of the reception at a Con-tinental studio-it may be overdone.but it is very agreeable to one aboutto face an ordeal. The artist is wel-comed as a friend, as a comrade in art.He is introduced to everyone in thestation, and is made to feel that theplace is at his service. Before heperforms, the artist has caught theatmosphere of a family party, andcan give of his best.

No Nerves at BrusselsOf all the Continental stations, I

award the palm to Brussels, for thewarmth of its welcomes. It is a smallstation, rather meanly housed-itoccupies merely the attic floor of abuilding devoted to companies con-nected with the Congo. But no onecould broadcast from Brussels and betroubled with nerves.

At Barcelona, too, the social atmos-phere is delightful, And there, itmust be remembered, the artist doesnot get the superficial politeness ofthe Castilian, but the natural courtesyof the Catalan. At Barcelona theyhave an excellent method of puttinga stranger at his ease-invariably anaudience is provided. This makesa wonderful difference-for theaudience is select and sympathetic.

Bridging a GulfThe. art of true entertainment

demands that the entertainer and hisaudience should be one; usually themicrophone breaks a vital link in thechain. But the gulf can be bridged bythe presence of a small understandingaudience in the room.

At Barcelona they specialise inproducing audiences which will res-pond to the artist's own mood. Hereis an idea for a new profession. Wehave professional performers-whynot professional listeners? Of thetwo, I would not say that the com-petent listener is the lesser artist.

WITH the increasing number ofshort-wave broadcasting sta-

tions in operation, there is a greatdeal of pleasure to be experiencedin these regions. The fact thatreception is obtainable from suchrelatively enormous distances (half-way round the world being achievedat certain times with clock -likeregularity) adds considerably to thefascination of listening.

A Little ProphecyOne feels inclined to prophesy that

in a little while short-wave receptionwill become much on a par withordinary broadcast working andevery enthusiast will have a short-wave set permanently wired togetherwith his broadcast receiver, so thathe can switch over to his programmefrom America, Australia, or someother part of the world whenever hefeels disposed.

It was determined quite early inthe days of wireless transmission thatthe absorption of waves by the atmo-sphere increased rapidly as the wave-

assumption that reception on shortwaves (below zoo metres) would bequite impracticable.

Moreover, as the frequencyincreased so the stray capacityeffects became more and moretroublesome and such difficultiesas hand -capacity effect becamevery pronounced. All thistended to the production of amyth regarding short wavesthat they were exceptionallydifficult to handle.

Long-distance WorkAs a matter of fact, this is

not the case. Amateurs, drivenlargely by regulations to experi-ment below zoo metres, found

Fig. 2a.-Straightforward Reinartz Circuit

that long-distance reception wasindeed quite possible on such wave-lengths. They found certain difficul-ties due to the higher frequenciesemployed, but these were success-fully overcome and, to -day, we areworking satisfactorily on frequenciesten to fifteen times as great as thoseemployed on the ordinary broadcastband with the same facility as ob-

JaMed with an ordinary receiver.The principal point to be remem-

necessary on short waves owing tothe fact that the modulations occupya relatively smaller space.

A telephony modulation willoccupy about a s o,000 -cycle band.At a frequency of i,000 kilocycles(one million cycles per second) thisis i per cent. At a frequency ofso,000 kilocycles, corresponding to3o metres, this difference is only.5 per cent. Thus, if we are tuningwith the same value of condenser, the

31

actual space occupied on the conden-ser will be only I, /To as great, whichmeans that the tuning is extremelysharp.

In practice, largely owing to thiseffect, we utilise rather smaller con-densers, and a value of about.000s3-microfarad instead of .0003-microfarad is more usual, since thisproduces a discrepancy of the orderof 3 to s instead of so to i.

Slow-motion dials or slow-motion

-------.co,t,

COtillEIMEA

(b)

condensers are essential, and a cer-tain amount of care must be takento avoid extraneous noise in thisconnection. For example, if thereare two rubbing surfaces in the con-

of dis-similar metals, thereis a danger from contact potentialeffects, so that when the condenseris rotated, cracking noises may beobtained.


By J. H. REYNER, B.Sc.,A.M.I.E.E.

bered is this large difference in fre-quency. Any effect which tends toincrease this frequency, therefore,will be more pronounced on the shortwaves. Hand -capacity effects havealready been referred to, these beingdue to the capacity between theoperating parts of the set and the

Figs. la. and lb.-How a Short.

av e Tuner canbe connected up

(a)

body. Therefore, as far as possible,all parts with which the hand comesin contact must be arranged to beat earth potential or connected tothe low-tension terminal.

of a metal panel is oftenemployed on short-wave sets sincethis acts as an effective capacityscreen and obviates such capacityeffects. Another important pointlies in the greater sharpness of tuning

Pigtail DifficultiesThis is sometimes obtained with

pigtails if this has several convulu-tions which touch as the condenseris rotated. Small short-circuitedloops are formed in which currents areset up momentarily every time acontact is made or broken and thisresults in interference. The diffi-culty is not usually serious, butoccasionally gives trouble. Diffi-culties have been known to arise dueto noisy slow-motion dials, contactpotential effects being set up by themechanism of the dial itself.

Apart from any electrical featuressuch as this, it is necessary that thedial or condenser shall give a verysmooth and steady action withoutany backlash. It may not be pos-sible to observe such backlash byeye, yet on tuning, it is found that ifthe dial is rotated one way and thenrotated back again a small amount,it does not tune -in the station oncemore, but either lags slightly or goes


Successful Short-wave Reception (Continued)

too far and runs right through therequired point.

Such points as these, of course, aretaken into account by the designersof short-wave apparatus, and con-densers used in WIRELESS MAGAZINEshort-wave receivers may be reliedupon to be satisfactory since theyhave actually been tried in operation.

Various FactorsIn the design of a short-wave

receiver various factors have to beexamined. While it is true that aset capable of operating satisfactorilyon short waves will also work excel-lently on broadcast wavelengths, theconverse of this is not true.

Owing to the very high frequenciesinvolved, it is necessary to use smallinductances of the order of 5 or tomicrohenries only, and these consistof a very few turns of wire. Indeed,on the very short waves the tuningcoil itself may possess only three orfour turns, and in such circumstancesthe actual length of wiring in thereceiver may have some consider.able effect.

Permissible Long LeadsThe principal point to remember

here is that any long leads whichmay be necessary must not be in-cluded in the actual tuning circuit.The leads from the tuned circuit tothe valve may be fairly long withoutcausing any serious difficulty.

This point is better explained byreference to Fig. I. Here two alter-native arrangements are shown forwiring a tuning coil to a variablecondenser, and connecting the tunedcircuit to a valve. In the firstplace the lead to the valve is keptvery short and the leads connectingthe coil and the condenser are longand far apart. There is thus a com-pletely closed loop of wire as indi-cated, and such a loop may have aninductance equal to, if not greaterthan, the short-wave tuning coilactually in use.

Better LayoutThe second layout is far better, for

the tuning circuit is wired with rela-tively short leads, these leads beingkept comparatively close together.There is then a longer lead to thevalve, but this lead is not carrying anyappreciable current. It simply serves

to transfer. the voltage developedacross the circuit to the valve, and,therefore, beyond a certain smallleakage due to the capacity -current,no serious difficulties will result.

The principal case where difficultywould occur from such a cause in asimple single -valve detector circuitwould be in obtaining the necessaryoscillation. Often it is found thata circuit rigged up as a perfectlystraightforward Reinartz arrange -

Fig. 3-In this circuit reaction iscontrolled by a shunted condenser

ment will refuse to oscillate, and on acloser inspection it is found that thereare closed loops in the wiring givingsufficient coupling in the wrong direc-tion to nullify completely the effectof the deliberate reaction provided,so the circuit will not oscillate.

Clearly in any case where high -frequency amplification is used, thispoint must be given particularattention and the possibility of high -

5..0

+Fig. 4 This circuit shows the use

of a short-wave choke

frequency amplification on short-waves is not by any means too remote.There are, indeed, one or two arrange-ments already in existence wherebygood and definite amplification canhe obtained prior to the rectifiervalve.

This question of reaction is one ofgreat importance for, when using asimple detector valve, it is clearlynecessary that the circuit should becapable of being brought right up to

32

the oscillation point. The valve isthen in its most sensitive conditionand will give a very large amplifi-cation, and it is only under such cir-cumstances as this that satisfactoryreception is possible.

To do this, it is necessary first of allto ensure that the layout is good and,secondly, that the reaction is smoothin operation. The first point lieswithin the province of the designer,while the second point is also verylargely under his control. It is usualto vary the reaction effect obtainedby means of a condenser inserted inthe reaction lead and some modifi-cation of the Reinartz principle isusually employed. Various possibleforms of circuit are shown here.

Reinartz CircuitThe first (Fig. 2) is a straightforward

Reinartz circuit, the variable conden-ser 'being so arranged that its movingplates are at earth potential to avoidhand -capacity effects. This is mostimportant. The second method isshown in Fig. 3 in which a perman-ent reaction effect is arranged, thecurrent passing through this beingshunted by the condenser. Increas-ing this variable condenser causes theoscillation to cease.

Third VariationA third variation is shown in Fig.

4, where the impedance of the tele-phones and batteries in series isallowed to act as a choke. Thisimpedance is shunted by a variablecondenser and as the value of thecondenser is increased so more andmore reaction effect is produced. Ifnecessary, a high -frequency chokemay be deliberately inserted at thepoint S.W.C. in this circuit, such achoke being one of the short-wavecomponents specially designed forthis class of work.

Good and Smooth ReactionAny of these circuits properly

arranged will give good and smoothreaction provided that the detectorvalve is operating satisfactorily.This is, perhaps, the most vital pointof all, it being necessary to ensure thatthe detector valve is operating on asatisfactory part of its characteristic.There are various ways of accom-plishing this; one of the simplest is toprovide a variable grid leak for the

detector. The grid leak must be of atype which will give silent operation,as any crackling or other noise willimmediately spoil the reception.

Value of PotentiometerAnother very good way of achiev-

ing the required results is to connectthe grid leak, not to low-tensionpositive, but to a potentiometeracross the low-tension battery. Withthe grid leak connected to low-tension negative the reaction is verysmooth, but the rectification effi-ciency is impaired. As the sliderof the potentiometer is moved overtowards the positive side, so thestrength gradually increases until apoint is reached where the reactionbecomes ploppy or jerky. Just be-fore this point is the best operatingcondition.

When the best arrangement hasonce been found it can be left set,so this potentiometer can be mountedon the baseboard if desired. Theactual setting depends upon thevalves in use. A final point is thatit is usually preferable to take H.T. -to L.T. - , as this again gives smootherreaction in practice.

Special PointsThese are some practical points

of interest to the short-wave worker.There are numerous points which canbe discussed in this connection andit is impossible to go into these allin one short article. In general,however, one can summarise in thefollowing terms :-

r.-Always follow the actual lay-out given by the designer as far aspossible. The apparently trivialalteration of a wire may make aconsiderable difference to the opera-tion of the receiver.

2.-Read what the designer has tosay about the operation of the re-ceiver. He will tell you its variousidiosyncrasies, and indicate the wayof obtaining the best results.

VALVE -LEG SPACINGVALVE -LEG templates are handy

V things, but often when neededmost they are not to be found. Hereare the actual measurements betweenthe centres of the various legs, sothat, at a pinch, a template may bedispensed with. Grid and plate -legcentres, 21/32 in. apart; filament -legcentres, /a in. apart; distance bet-ween filament -leg centres and grid -leg centre, in a line parallel with thatjoining plate and grid, V4 in. But.


Broadcasting Organsand urganestras

WITHIN the last year or soorgans of the " Wurlitzer "

type have sprung into favour in allthe modern " super " cinemas, andas the conditions are eminentlysuitable for broadcasting, the peculiartones of cinema organs will be wellknown to most listeners.

The music, as primarily suitablefor film -play accompaniment, isalways of the " popular " variety, ormettzo-brow, as one might say.

TO A FICKLE JADEWho is using a Television Instrument

Though thou sayest withdecision

Thou art sad without me,Grace,

Thou forgettest television-'Tis refuted by thy face.

Thou hast told me that thouyearnest

To be with me, to be hereBut I see the face of Ernest

(Nasty blighter! lurkingnear.

Television oft reminds us,Though Love's dream may

seem sublime,There are other chaps be-

hind usAnd thou flirtest all the

time!

.1111111111.

Leslie M. Oyler

That makes it very acceptable tomany.

Cinema organs differ from con-ventional church organs in verymany respects; in fact it is hardlycorrect to refer to the former as"organs." They are, more correctly,organestras; they replace a combina-tion of organ and orchestra.

Most of the pipes are reeds, that is,they produce sound by the forcingof air against a metal lip enclosed inthe pipe, exactly as is done in a motorhorn of the bulb variety. Thisproduces the reedy tones which arepeculiar to cinema organestras and to

33

the " swell " manual of church organsChurch -organ pipes, for the mostpart, are giant penny -whistles, andproduce sound by blowing air againsta sharp -edged lip. There are acertain number of reed pipes in achurch organ, however.

Best for BroadcastingThe reed tones are more suited

to broadcasting, owing to the peculiararrangement of the harmonics. More-over, the lowest bass notes of anyinstrument do not broadcast well.Cinema organs, as a rule, do not havevery deep " pedal " notes, whereasmany church organs have pipes 64 ft.in length, giving notes too low toreproduce well on most loud -speakers.

The " quivering " of cinema organsis caused by a fan placed in the mainair duct, and while high -brows maynot always approve of the persistentuse of this device, known as thetremulant (which is fitted to, butseldom used on most organs for" serious " work) it certainly breaksup the reedy tones and makes themmore acceptable.

It is generally known that organshave more than one manual or rowof keys. Most "organestras" have twomanuals, and there are, of course,literally hundreds of pipes in con-nection with each keyboard. Cinema -organ pipes are all enclosed in largecompartments, known as swell boxes,fitted with a moving front like a vene-tian blind. The volume of sound isregulated by opening or closing theseshutters.

Easy for the EngineerFrom the broadcasting engineer's

point of view it is easy to arrange aposition for the microphone in whichit will be at an equal distance from theone or two swell boxes.

In the case of church organs, how-ever, the pipes are not always grouped.Some may be close by the " console,"or keyboards, while others may bein a different part of the building.This increases the difficulty of micro-phone placing, and hence theengineer's fondness for the "oneunit" cinema organs. DIAPASON.

Wireless Magazine, August, 19;8

IERIKPORNBIt

BY dispensing with a loud -speakerand using headphones the bulk

and weight of a portable set can becut down very appreciably, sincethere is no need for high amplificationand large power output : whilst, inaddition, it is possible to use a muchsmaller frame aerial, which meansthat the dimensions of the cabinet canbe reduced.

Headphones have been condemnedby some as uncomfortable andunsociable, but still they have theiradvantages; and under some circum-stances, can be used where loud-speakers are out of place.

Good for a Walking TourThe object in designing the

Pilgrim was to build a set whichcould be called portable in the truesense of the word; a set, in fact,which might be taken by oneperson on a walking tourwithout adding appreciably tothe bulk or weight of hisbaggage.

The receiver, for which con-structional details are given inthis article, is housed in a cabinetmeasuring only 13 in. by i i in.

An Unobtrusive Headphone Set for the Holidays : De-signed, Built and Tested by the "W.M." Technical Staff

by 6 in. ; whilst the weight, completewith batteries and headphones, isalmost negligible.

Both in daylight and at night loudphone reception is obtained from thelocal station within at least fortymiles and from DaventryExperimental withinat least ioo miles.There would be fewplaces in this countrywhich would be outof range of one sta-tion, whilst in mostparts two stationscould be heard.

From a glance at thephotographs it can beseen that the interior ofthe cabinet is divided intoseveral sections. The setitself fits into the top compartment;immediately below this is a compart-ment for the 6o -volt H.T. batterywhich has tappings for grid bias. Atthe side an unspillable C.A.V.accumulator is housed, whilstimmediately above this there is spacefor a pair of headphones.

The back of the cabinet, which is

Here is the PilgrimPortable from the back

34

made of three-ply wood, supports theframe aerial : this must be removedin order to inspect the H.T. and L.T.batteries. The headphones can bereached by opening the hinged flap infront of the cabinet, which exposes the

Plan view of the Pilgrim Portable

tuning controls. A leather strap isfixed to the top of the cabinet so thatthe set can be carried when broad-casting is actually being received.

Ideal Portable CircuitSome experiments were made with

the object of finding an ideal two -valve circuit for portable use; it wasat first doubtful whether a straight

two -valve circuit would be suf-ficiently sensitive to operate with avery small frame aerial. Accord-ingly attempts were made to obtaina stable reflex circuit, but theresults did not justify the extracomplications and distortion whichseemed to be unavoidable with thistype of circuit.

Finally the straight two -valvecircuit with a detector and oneL.F. amplifier was chosen, since itgave the required results whilstbeing more stable and simple tooperate.

From an examination of the cir-cuit diagram, it will be noticed that

both the grid and reactioninductances are included inthe frame winding; withthis arrangement, the re-action is almost constantthroughout the tuning

range-a boon to the operator.In consequence 5GB and the local

3/e.


------- MAGAZINE, 58/61 Fetter Lane,

0',/ ,'a',4> Milt STRIPS 3°X 144( V4

16 5LOT6 Ye"APART In EACH

/tt ie; 2311.T. C.

TAPTAPPIIIC AT4'2' TURIt F11011

IM910E.----1.

')\\

Bn

'1/47

A

Details of the frame winding for thePilgrim Portable

station could be received well withoutaltering the reaction condenser,although the latter was uncomfort-ably loud for the headphones andcould be heard on the loud -speaker.

The Wearite H.F. chokeundoubtedly helps in obtain-irig constant reaction controland also prevents H.F.oscillations from getting intothe L.F. amplifier and caus-ing distortion. One of thenew Philips transformershas been used since its com-pact size and large primaryinductance, combined witha step-up ratio of 3 : 1, makeit particularly suitable forportable sets.

Compact CondensersThe compact size of the

variable condensers, used for aerialtuning and reaction, make it possiblefor the size of the panel and baseboardto be kept small. These condensersare controlled by diminutive slow-motion R.I.and Varleydials, whichon accountof theirsize andsmoothmotion aremost suit-able for asmall port-able set.

No diffi-culty will be

E.C.4.Since the panel measures only

9 in. by 6 in. and the baseboard9 in. by 41 in., the componentsmust be spaced carefully. It isadvisable first of all to drill theholes for the variable condensers.It is necessary to place a fewwashers behind the panel in orderto prevent the single -hole fixingsleeve of the variable condenserfrom extending beyond the fixingnut and, in con-sequence, keepingthe dials awayfrom the panel.

As soon as thecondensers aremounted on the panelthe latter can be

(Above) Tuning -in the Pilgrim Portable.(Right) A happy half-hour out of doors

placed up against the baseboard andthe L.F. transformer mounted on thebaseboard exactly between the twocondensers. Then the remainingcomponents, consisting of the valve

holders,

FRAME

Circuit of the Pilgrim Portable

encountered in the construction ofthe Pilgrim Portable if use is madeof the full-size blueprint. This is No.W.M.94, and can be obtained for half-price, that is, 6d. post free, if thecoupon on page iii of the cover is usedby August 31. Address your inquiryto Blueprint Department, WIRELESS

H.F. choke,and gridleak, withcondenser,can be fixedin position.

Place thevalv eholders suf-ficiently farfrom thevariablecondensers

to allow insertion of the valves. Thegrid leak and condenser will have tobe mounted behind the first valveholder, since there is insufficientroom in front.

As soon as the components arescrewed into position, the two tele-phone terminals and " on -off " switrkk

35

can be mounted on the panel.

No Difficulty in WiringThe actual wiring should present

no difficulty; it will be simpler tocommence with the grid leak andcondenser, as this component is notfully accessible and might be furtherobstructed by leads from the aerial -tuning condenser. Connect the mov-ing plates of the aerial condenser topositive filament, in order to reducehand -capacity effects when tuning in.

A short length of red and blacktwin flex terminating with plugs,forms the connections to theH.T. battery; whilst a similarlength with spade connectors

is taken to the L.T.accumulator. A singlelead only from the " G- "terminal of the L.F. trans-former is required for gridbias. Otherwise, wire upin the alphabeticalsequence indicated on thewiring diagram.

Winding the frameaerial requires a littlecare if it is to look neatand fit properly into theback of the cabinet. The

1

Wireless Magazine, August, /928

View of receiver portionof the Pilgrim Portable

total thickness of the Is in. plywoodback and winding must not exceed

in. ; therefore -A. in. is allowable forthe thickness of the winding supports.

Supporting Strips for WireWith a small hand -saw or fret -saw,

The Pilgrim Portable (Continued)

at a distance of 3/4 in. fromthe corners and screw themin position with in. brasscountersunk screws. The

winding may then becommenced with No. 22d.s.c. or d.c.c. copper

wire, first anchoringthe end by windingit round a smallbrass screw fixed inthe back. Pull each

turn fairly tight, but do not over-strain the holding strips.

When the full twenty-three turnshave been wound on, the end may beanchored to the back. It is advisableto stick a strong piece of paper ormaterial over the grooves which carrythe winding; Seccotine is an admirableadhesive for this purpose.

The winding must now be tappedat four turns from the insideend. Flexible leads are takenfrom this tapping to filamentpositive, from the inside endto the reaction condenser,and from the outside end tothe grid leak and condenser.

The Pilgrim can now befinally assembled. Fit thepanel and baseboard into itscompartment, pushing thepanel back sufficiently toallow the hinged flap on theoutside of the cabinet to shutwithouttouching the controls.Holes should now be drilledinto the various compart-ments for the battery andphone leads.

As soon as the batteriesare in position andconnected up, thevalves may be insertedin the holders andthe frame aerialclamped in place.The grid -bias leadfrom the L.F. trans -

000ROVP1CACCT -55TO PAIIELCOtITHOT5

SPACE FORPPM L5

,PAC. f. FUfiP5 TO

Mill FRAMEAERIAL

M.T. COMTATTI MAT

L7 CDMFARTrun

Details of cabinet for the Pilgrim Portable

IF YOU WANT A REALLY GOODLOUD -SPEAKER PORTABLE BUILDTHE CHUMMY FOUR.-FULLYDESCRIBED IN THE JUNE ISSUEOF THE WIRELESS MAGAZINE

cut 4 strips of fe in. three-ply wood,measuring 31/2 in. by 3/4 in. At adistance of I in. from the end cut asuccession of twenty-three groovesspaced in. apart in each strip, usinga saw and slanting the groovesslightly in order that the frame wind-ing will hold itself in position.

Winding the Frame AerialPlace the strips at the corners of

the plywood back, pointing diagonally

former should be pluggedinto the negative end ofthe H.T. battery and thenegative H.T. lead putin the battery socket,giving from 3/4 to3 volts positive.

The set is nowready for use.Switch on the L.T. supplyand rotate the reaction condenseruntil the set is just oscillating.

36

COMPONENTS REQUIRED1-Ebonite panel, 9 in. by 6 in.

(Becol, Radion or Parfait).r-.0005-microfarad variable con-

=denser (Peerless).r-.0003-microfarad variable con-

denser (Peerless).2-Anti-microphonic valve holders

(W.B., Lotus or Benjamin).2-Vernier dials (R.I. and Varley).1 -.0003-microfarad fixed conden-

ser (Graham-Farish or Lissen).I -2-megohm grid leak (Graham

Farish, Lissen or Dubilier).I-High-frequency choke (Wearite,

Cosmos or Magnum).i-Low - frequency transformer

(Philips).I-On-off filament switch (Bulgin,

Lissen, or Lotus).r -60 -volt high-tension battery

(Ripault, chocolate label).I -2 -volt unspillable accumulator

(C.A.V. type 2NS9).2-Terminals, marked : Phones + ,

Phones - (Belling -Lee).1-Cabinet (Pickett's).

Operate the aerial -tuning condenseruntil the strongest carrier wave isheard; then rotate the entire cabinet.There will probably be one positionof the cabinet when the carrier wavewill become very weak : setso that it is facing at right angles tothis position and decrease the reactionuntil oscillation ceases. Then retuneuntil comfortablestrength is obtained.

Suitable Valves for the PilgrimA number of different types of

valve will work efficiently in. this set ,

perhaps the best combination is amedium -impedance valve (20,000 to30,000 ohms) for the detector stage,and an L.F. valve with an A.C.

Another view of thePilgrim Portable


For Really Good Headphone Receptionresistance varying from ri,000 to22,000 for the final stage. Since anL.F. transformer having a highprimary impedance is used someadvantage may be obtained by usinga fairly high impedance valve (40,000to 6o,000 ohms) in the detector stage.An ultra high impedance valve is notrecommended.

Almost any headphones can be accommodatedwithout difficulty in the Pilgrim Portable, andthose who wish to keep down the cost of construc-tion will find a pairof Lissen phones verysatisfactory. Thisphotograph shows apair being packedinto position at theend of a pleasantafternoon's outing

TECKED BY

41L

PLATES

4-2 Ye:

REACTIONCONDENSER

MOWNG PLATES

TOLT+

L.FTRANSFORMER\

L.F. VALVE

TO LT-HT -

3/8

MOMS -

TOGB -

TO TAP011 FRAME,

h

TO 11T+

BLUEPRINT N9WM 94

z14

3/5"

FIXEDPLATES

TO 'AON FRAME

c oNTPRI/L3E.

MOVING PLATES

PA11EL 9"xe;

Aii.51.BOARD

JVALVE

This layout andwiring diagram ofthe Pilgrim Port-able can be ob-tained as a full-sizeblueprint for half-price, that is 6d.

post free, if thecoupon on page iiiof the cover is usedby August 31. Askfor No. W.M.N.When wiring upfirst connect thosepoints marked a;then those pointsmarked b ; andso on, in alphabeti-

cal sequence

Toy Balloons1( 1 :CENTLY, I witnessed an

interesting little laboratoryexperiment which gave me " furiouslyto think" about ionised air, theHeaviside layer and similar matters.

Two balloons were each suspendedon silk thread and slightly chargedstatically so that they repelled oneanother. A small X-ray tube(working from a quarter -inch sparkcoil) was then set in operation and anX-ray beam projected towards theballoons.

Immediately the beam came intheir locality they fell from their erectposition as though the static electric

and X -Rayscharge had suddenly leaked away-as, indeed, it had.

The X-rays ionised the air andmade it impossible for the balloonsto retain their mutually repellingcharges.

If there are natural X-rays-byno means a physical impossibility --they must exert a similar effectupon non -ionised air near the Heavi-side layer, and perhaps increase itsdepth.

Incidentally, this balloon ex-periment is the basis of a simplemethod of measuring the intensityof X-rays. QUEUE.

37

DifferentCrystal Circuits

"THE humble crystal set," asI some people call it, does not,

sad to say, present so much opportu-nity for stunt -merchants' activities asdo valve sets.When All Is Said

By this I mean that, when all is saidand done, a crystal set consists of atuner, a detector, and a pair ofphones. One may have phone -shunting condensers, dual detectors,unique tuning arrangements and soon : but the basic circuits are notreally altered.

Crystal sets have not yet reachedfinality, however, because, relativelyspeaking, their present actual signalefficiency is poor. Chiefly this is dueto detector resistance, and to over-come this it is possible to use twodetectors simultaneously. This canbe done by placing the detectors inparallel in an ordinary. set, but withH.F. chokes in each of the leads fromthe detectors to the phones. Thephones are thus in the commoncircuit. Without the H.F. chokesthe arrangement will not work at all,as one detector will "short" throughthe other.In the Shadow

The advantage of using two detec-tors to lower the resistance is to befound when a set is worked rightunder the shadow of a broadcastingstation, and one detector alone mayhave a limiting effect. P. K.

Wireless Magazine, August 1928

the.Notet8 withPto

A CHAT ABOUT SCREENED -GRID VALVES

" T SAY, Professor," said young1 Amp one day, as Megohm and

he were out for a stroll, "what arethese screened -grid valves that peopletalk about such a lot now ? "

Megohm smiled. "You're insatiable,aren't you Amp ? " he said, shaking hishead sorrowfully. "Here we arewalking along a perfectly goodcountry road in perfectly good sun-shine-"Still Wireless

" With perfectly good grass in thefields and perfectly good birds in thetrees," chanted Amp, "and still Iwant to talk about wireless. Is thatwhat you meant to say ? Well,anyhow, why shouldn't I?"

"I suppose there is no reason whyyou shouldn't," said the Professorhalf regretfully. "What was it youwanted to know, anyway ? "

" Well, I thought perhaps youmight spill a few beans about screened -grid valves."

Megohm shuddered. Then : " Whatabout them. I suppose you've seenone ? "

" I saw one at the last Exhibition,but that didn't help me very much.It seems to have two ends to it,anyway, and I couldn't tell whichway up it was and that's about all'cos I could not afford to buy one."

Megohm's MagicMegohm put his hand in his capa-

cious pocket and produced a screened -grid valve and a pair of pliers. Amp,speechless with amazement, watchedhim return the pliers quite uncon-cernedly to his pocket, after which heheld the valve up between his fingerand thumb. Then, as he caught sightof the boy's astonished gaze he said :`Why, what's the matter, boy? Youdon't think it will explode, do you ? "

" Do you mean to say that youcarry valves about in your pocketlike that-all mixed up with pliersan' things ? "

" Why not ? " said the other .with ashort laugh. " It's as safe as leaving'em on a bench to get knocked over.I don't usually. take them for a walkwith me, I admit, but it's ratherfortunate for you that I have. Iforgotto take it out of my pocket before wecame out to -day."

SCREENED -GRID VALVESETS FOR THE HOME-

STRUCTOR

The Screened -Grid Three,October, 1927 (page 219),Blueprint No. WM21.

The Chummy Four (portable)June, 1928 (page 399), Blueprint No. WM80.

The Screened -grid Four,June, 1928 (page 418),Blueprint No. WM77.

The All -the -world Five,March 1928 (page 107),Blueprint No. WM63.

A new screened -grid three-valverwill be described next month

Amp gulped. He could not helpfeeling that if he had one of thesetreasured screened -grid valves, itwould be kept very carefully wrappedin cotton wool, when it was not inuse and, in fact, he would hardlydare to use it for fear of breaking it." There's no hope for it," he thought," I'll have to become a Professor."

Arrangement of Pins"Perhaps,_ you will one day, my

lad," agreed Megohm with a smileand Amp, realising that he had spokenhis thoughts aloud, blushed furiously."In the meantime," resumed theProfessor, " let's have a look at thevalve. You will see that it has threepins at one end and two at the other."Amp nodded. " The three pins areconnected to the grid and the filament,and if you look you will see the

38

it1

triangular or V-shaped filament witha flat grid around it."

Here he passed the valve over tothe boy who very cautiously exam-ined it and distinguished for himselfthe filament and grid as the Professorhad said.

Fine Wire -gauge Screen"Now," continued Megohm, "right

across the whole bulb, forming a par-tition across the middle, is a wire -gauze screen. This is actually con-tinuous with a metallic ring whichruns round the side of the bulb.You can make that out although youcannot see the ring very clearlybecause the inside of the glass on theright-hand side of the screen issilvered, due to the gettering '."

" I had an uncle who lived thereonce," said the boy, gravely.

" Merciful heavens," exclaimed theProfessor in anguish. "A joke ! Doyou mean to tell me that you do notknow what gettering ' is?"

" Something to do with mag-nesium," said the boy, brightly.

How A Valve Is Silvered" A little vague, but on a par with

your average intelligence," was thereply, at which Amp grinned. "Whena valve is made, a small piece ofmagnesium or other suitable sub-stance is placed on the anode. Duringthe exhaustion process the anodegets sufficiently warm to volatilisethis and since magnesium is a power-ful oxidising agent, it cleans up theresidual gas inside the valve. Theunused magnesium deposits itself onthe inside surface of the glass, givingthe silvered appearance as you haveobserved. However, that is quiteincidental. To resume our discussion.

"If you look through the gauzescreen which I have just told youabout, ,you will see the anode of thevalve beyond it. In fact, it almostlooks as if it were part of the samepiece of metal, but if you examine it

closely, you will see that it isseparate."

" I can make out something of thesort, Professor," agreed the boy." Then is the connection for thatanode brought out to the pins at theother end ? "

" It is brought out to one of thepins, the other pin being connectedto the screen or partition in betweenthe anode and the ordinary grid."

What the Screen is for" Oh, I see. Then the screen's

quite separate from the rest of theworks. What's it there for, anyhow? "

" It serves two purposes. Youknow yourself how high -frequencycircuits will oscillate due to back -coupling to the valves and you knowthat we often use neutralised cir-cuits which are really carefully ar-ranged bridges in which the effect ofthe valve capacity is balanced outby some other capacity."

Amp nodded, remembering thevarious times when the Professor haddiscussed neutralising with him.

Capacity Effectively Reduced" The presence of this screen be-

tween the anode and grid reduces theeffective valve capacity to some-thing very small indeed, as a resultof which this feedback through thevalve is practically eliminated."

"Gee," cried the boy. "That'suseful, isn't it ? "

" Very," was the laconicreply. " As a matter offact, however, this isonly part of the story,and is to some extent anincidental effect. For along time valve manufac-turers have been tryingto increase the amplifica-tion factor of valves. Wehave, indeed, with theordinary three -electrodevalve types having am-plification factors be-tween 3o and 40, but thedifficulty is that in orderto obtain such high am-plification factors the in-ternal resistance of thevalve has to he extremelyhigh. If we want to goany higher than this thevalve resistance rises sorapidly. that the valve be-comes impracticable."

" Why should that be,Professor ?" Ampqueried.


" Because we can only make use ofan amplification factor of a valve ifwe can make our external circuithave an impedance comparable withthat of the valve. Our external im-pedance is determined by certainpractical considerations, and there-fore we obviously cannot continue toincrease the internal resistance of thevalve indefinitely."

"I see," said the boy. "Then doesthis new valve get over the diffi-culty ? "

" Yes," replied Megohm. " Thepresence of the screen, which is keptat a fairly high positive potential,serve& to attract electrons from thefilament, thereby increasing theemission current. Consequently, wecan make a valve of the four -elec-trode type have a much lowerinternal resistance for a given ampli-fication factor than the ordinarythree -electrode type. As a matter offact, this theory is not strictlycorrect, but it serves to indi-cate the general actiontaking place."

" Then the valveacts just thesame as anordinaryvalve,

doesn'tit, Pro-

fessor ?"asked Amp.

Positive Potential" Very nearly so," agreed the

other, "the only difference beingthat the screening grid is connectedto a steady positive potential bytapping it on to a suitable point onthe high-tension battery, and that

39

this point has to be somewhat care-fully chosen to give the best results."

" Does it make very much differ-ence, then ?"

Varying the Characteristic" It does, because it enables us to

vary the characteristic of the valveto suit our own requirements-athing which we cannot do with theordinary valve. If we make thevoltage on the plate and screeninggrid both the same, it will be clearthat only small currents willflow through the plate it-self. The majority of theelectrons will stop atthe screening grid.and it is onlythose whichshoot

throughthe holes in

the screen thatwill pass on to the

plate or anode."'Amp nodded. "Yes, I can

see that," he remarked.

Increased Anode Current" Good. Well, then, as we increase

the voltage on the plate, so we beginto attract more and more electronsand cause them to shoot through theholes in the screen so that the anodecurrent increases. At the same time,the current actually flowing to thescreen must decrease because theelectrons which formerly went to thescreen now go to the anode. Conse-quently, we obtain anode current byrobbing the screen, and as we in-crease the high-tension voltage onthe anode this process will continue


Half Hours with the Professor (Continued)

until very nearly the whole currentwhich originally flowed to the screen-ing grid flows to the anode."

The boy remained silent, turningit over in his mind while the Pro-fessor continued his explanation.

" In the early stages a small excessof plate voltage over screen voltagewill cause quite a big current, butclearly as we take more and morecurrent away from the screen, theaction must fall off and we shallultimately reach a point where westop.

Resistance Increases Also" Now the internal resistance of the

valve depends upon the change inanode current which can be producedby a given change in anode voltage.Clearly, therefore, as we increase theanode voltage, the increase of currentbecomes less and less and thereforethe internal resistance of the valveincreases.

"As a matter of fact, the valvewhich you have just been looking athas an internal resistance of 150,000ohms, when the voltage on theanode is 96 volts and the voltage on thescreen is 8o volts, and at that point ithas an amplification factor of 6o."

Amp whistled. " Sixty did yousay? That sounds pretty good."

Megohm smiled. " We can do a bitbetter than that if you like. If weincrease the anode voltage to aboutiso, then the internal resistance ofthe valve rises to 450,000 ohms, thatis nearly three times as great, but atthe same time, the amplificationfactor rises to f 80."

Amp was thunderstruck. Anamplification factor of i8o ! Why,

you would not need any more valvesat all I

" You would have a little difficultyin getting 18o out of it," broke in theProfessor, realising the probabletrend of the boy's thoughts, "becauseyou would have difficulty in makingthe tuned circuit have an effectiveimpedance of anything like 450,000ohms, whereas in order to obtainthe full amplification factor from the

Madge Bellamy, whobroadcast recently

valve, we must make our externalcircuit many times greater. Thepoint is that you can vary thecharacteristics of a valve to suityour circuit by merely adjusting therelative values of the voltage on thescreen and on the anode."

" What sort of amplification doyou get in practice then, Professor ? "

" Between 3o and 40," was thereply.

"That sounds awfully good," saidthe boy. " Then do the internalresistance and the amplification factorremain proportional ? "

"Yes," answered Megohm, "withthis particular valve they do andthis is one of the important advant-ages over the ordinary three -electrodetype. With a three -electrode valve,if you wish to increase the amplifica-tion factor, you must alter the spacingof the grid wires or otherwise changethe configuration of the electrodes.When you do this, you find that theinternal resistance increases muchmore rapidly than the amplificationfactor does and, as I said at first,it is impossible to obtain an m valuemuch greater than 4o without exces-sive internal resistance.

Constant Ratio" With this valve, however, we

vary the characteristics of the valvewithout affecting the relative dis-position of the electrodes at all andtherefore the ratio of amplificationfactor to internal resistance-or themutual conductance as it is called --remains constant; as we vary thevoltages on the anode and screen, wecan vary the characteristics of thevalve almost indefinitely and at eachpoint the ratio of amplification factorto internal resistance will remainconstant.

" But," broke off the Professor."Bless my soul, if it isn't Mrs. Amp!What lovely weather we are having,to be sure," he said as he hurriedforward.

"And that's that," growled Ampto himself, " I shan't get any moreout of the old fossil to -day."

THE wavelengths of the B.B.C.stations are not always constant

and true to their designations. Oneof the southern stations is occasion-ally .5 metre above or below normallength.

"All that's broadcast is not broad,"said a listener who was listening oneSunday evening. His wife who wasknitting answered, "Neither is it cast."

Cologne has a reputation among theGerman stations of being the mostEnglish. There are broadcast lec-tures of no mean merit on English

MixedGrill

grammar and literature. However,the station reminds one of a bookpublished in New York a few yearsago, which was entitled EnglishLearned in Twelve Lessons. But thenGermans are prodigious learners andprolific scholars.

In a few years time it will not be aneasy task for the B.B.C. to get all the

40

anniversaries, centenaries, and ter-centenaries into the year's programmeif the policy adopted this year so faris to be persevered with. It is strangehow many non-musical men seemto have celebrations in their honourjust now.

It is assumed that there are twelvemillion listeners in the British Isles.One authority assumed further thatten million of these listen on anaverage evening. In a street wherethere are eighty listeners not one waslistening on a particular evening lastweek,


PotazeeilReaders of the " Wireless Magazine " who are thinking of designing their ownportable sets will find this article by Capt. H. J. Round, of considerable

help in choosing the most efficient circuits

WHEN we couple cwo valvestogether or couple a valve to a

crystal, an electrical network is usedand this network takes on different:orms far different purposes.

Thus in its simplest form it becomessame arrangement of resistances andcondensers of which the commonestform is shown in Fig. r which dia-gram pretends to illustrate the actualcondition of affairs. But if we couldassume that this arrangement reallyrepresented the facts, some branchesof our art would be very muchsimplified

Practical Need OnlyI may note that the reason for

the resistance, capacity, resistancearrangement in this combination is, ofcourse, only a practical one, as, butfor the presence of D.C. voltages, wecould avoid the necessity of thecondenser and second resistance-andin general we design this condenserand second resistance so that theaction of the circuit over the par-ticular frequency range in which werequire good working is the same asthough they were not there.

In effect, we really need only con-sider what results between theinteraction of the first valve and itsresistance, and then we can assumethat the voltage produced across thisresistance is applied directly to thesecond valve. With normal valves, atlow frequencies, magnifications of 20to 3o are quite realisable by means ofresistance -capacity coupling.

Amplification ObtainableThe low -frequency a nplification of

valves with resistance in the platecircuit are given by the formulaM R

Rv,where M is the magnifi-

cation constant of the valve, Rvits resistance and R the externalresistance. Thus if R is small com-pared with Rv the magnification issmall and if R is large then themagnification approaches M.

These values of M and R are thosegiven by the valve makers, butaccurate calculations always have tobe done with the curves, becausealthough M is roughly constant for allconditions, Rv varies a lot with theadjustments of the valve.

Fig. 1.-Common form of intervalvecoupling

A similar formula applies if theexternal circuit is an impedance,either due to capacity or inductance,or both.

The capacity of the valve has to betaken into account at the higherfrequencies for, instead of being able

Fig. 2.-This arrangement gives goodamplification at low frequencies butfails at high frequencies because of

the valve capacity (shown dotted)

to consider a plait+ resistance in theplate circuit, we have to think of thisresistance as shunted by a condenserequal to twice the valve capacitybecause, of course, there are twovalves across the coupling networkas a usual thing.

41

In addition, there is a straycapacity due to the resistance itselfand the wiring, resulting in a totalvalue which may amount to asmuch as .00003-microfarad withmodern valves.

Manufacturers' PrejudiceUnfortunately valve makers have

fought bitterly against the intro-duction of low -capacity valves. Anyvalve which differs from the tradi-tional four -pin standard is damned atonce and our art is being handicappedby the inability of the designer toforce valve design in the directionreally required. I introduced as farback as 1916 extremely low -capacityvalves-the V24 and Q type-butthese valves were declared to beunmakeable in mass production.

With such valves, resistance -capacity couplings become quit(manageable down to 300 metres,although the magnification at thatwavelength is not too large, but ifthe circuit designer could really havehis way, R.C. coupled valves withH.F. magnification up to zo at 300metres could quite easily be pro-duced.

However, here we are with large -capacity valves, and we have got tofind out how to use them underpractical conditions.

Balancing Valve CapacityLet us take the arrangement of

Fig. 2 (which gives good magnifi-cation at low frequencies, but whichfails at H.F., because of the valvecapacity) and across the resistanceR put a network LC which we willinitially suppose is a combinationwith no losses in it. (Fig. 3.)

Such a shunt combination of L andC will have an impedance dependingupon the frequency which is beingused and it is well known that thisimpedance is infinite at the resonantfrequency, so that at that frequency wecan assume the magnification will be


Intervalve Couplings for Your Portable ! (Continued)

Fig. 3.-Previous circuit with additionof network LC

the same as would be obtained with thevalve and R alone on low frequency.

It will be noted that the effect ofthe valve capacity is wiped out bybeing absorbed into the tuningcapacity C.

This effect, however, is only at thepoint of tune and we must examinecarefully what happens away fromthe tuning point, for in certainreceivers there will be no tuningarrangements.

Impedance of the NetworkApproximately we can say that

the impedance of LC is equal towhere N is the difference of

47rNc,the frequency we are using from theresonant frequency. Obviously thelarger N is the smaller the impedanceis, and as this impedance shunts theresistance R the magnification mustfall off, as the difference from tuneincreases.

But note that the smaller C is, thelarger the impedance is, so that if Cis small we can go farther from thetuning point and get good magnifi-cation or, vice versa, if we want verysharp tuning, C should be made large.

The lower limit of C is obviouslygiven when it represents only thevalve capacity, and this arrangementis in a modified form now used inportable receivers.

For Portable ReceiversIn these portable combinations, a

large inductive winding is arrangedto be in tune with the middle of thebroadcast band, and the amount ofmagnification possible at the twoends of the band is to a great extent amatter of luck-no tuning usuallybeing done except by switching to anew set of coils.

Grid -anode capacity with ordinaryvalves makes the calculation ofcircuits-particularly those with a

small value of condenser C, and largeinductances in the network-almostimpossible, but some attempt can bemade with the shielded valve toestimate what can be done.

Before showing the effect morequantitatively of this network, I mustpoint out that the resistance R neednot be a real resistance and actuallyin most cases represents the loss inthe LC circuit.

Thus a tuning coil with a seriesresistance R(series) will actlike a coil with ashunt resistanceR (shunt) if

R(shunt)C R(series)

Suppose wenow wind up someinductances andestimate on thevalues involved.A Litz inductanceof 200 micro

paratively low resistance in mostcases and we shall only have to takeaccount of the L and C values.

In sharply -tuned receivers the coillosses enter quite seriously, but in thesemi-aperiodic arrangements of port-ables we can almost neglect them.

Some Practical EstimatesI am now going to use the informa-

tion we have obtained to estimatewhat will happen in a number of

cases and the

MOO

CM IC5.

.00003 c -3

FROM 80TO fall

Fig. 4.-Screened-grid valve circuit

henries will wind up quite easily toabout 6 ohms series resistance. Acoil of about the same dimensionswith twice the number of turns willhave four times the inductance andfour times the resistance (series).

Tuned to 36o metres in each case,the equivalent shunt resistances willbe 200,000 ohms and 800,000 ohms.

Wave-length

250metres

360metres

500metres

Frequency 1,200,000 833,000 600,000N 367,000 0 233,00oI

r8,300 infinite 12,000

4TNCA oX 5 100 715. 'L F, = 20 5 20 7

81 6 3.8 6 4.5

Fig. 5.-Magnification obtained fromthe circuit arrangement of Fig. 4

As the general coils in portablesare even higher inductance than this,even if wound rather inefficiently,their effective shunt resistance will beso high that this resistance can beneglected in calculations-particu-larly as the valve will be of cora-

42

valve I propose touse is a shieldedone, so as to avoidinteractionbetween grid andplate circuits.

I have shownelsewhere that themutual con-ductance of ashielded valve(r) remainsairly constant

over large ranges of plate volts, butthat M and R vary from quite low tovery high values.

Thus in a particular casewas .6 milliamperes per volt, but Mcould be varied from 4 to zoo bysimply varying the plate voltageand, of course, R was likewise varied.

Shielded Valve CircuitLet us see what will happen if we

put such a valve into connection withan LC circuit in which L is 1,20omicrohenries and C .00003 microfarad(Fig. 4). Let us choose severalsettings of M - say, 5, 20, andtoo, and calculate out the resultingmagnification.

In the table Fig. 5 I gave themagnification at 3 points --25ometres, 36o metres, and 500 metres,in all three cases.

It will be seen that if we were tochoose an M value such as too, themagnification at 36o metres wouldbe very great-in fact, with twostages, it would be unmanageablybig, whereas at the limits of 25o andSoo metres it would be quite small.

Unpractical ArrangementThis arrangement would not

make a practical non -tuning coilarrangement. But the 20 Mvalue is better, and the 5 Mstill better-one might say that


An Exclusive Article by Capt. H. J. Round, M.I.E.E.

this latter arrangement was fairlyflat in tuning.

If we had an arrangement in thecircuit of the valve plate so that thevoltage was fully under control, wecould choose our voltage so that thecircuits were just stable and it isfairly obvious that if two sets of theseinter -coupling arrangements are used,it will be wise to stagger theirresonance points, making one sayabout 30o metres and the other 430,or thereabouts.

Variation of plate volts could easilybe done by a series variable resistanceof high value, shunted with acondenser.

Transformers or ChokesIn actual practice, two such L

values (Fig. 6) well inter -coupled tomake a transformerare usually used, butI am not at all surethis could not bepreferably replaced bya simple L with a gridleak and condenser(Fig. 7), as such atransformer is liable toincrease capacityeffects more than thegrid leak and con-denser.

As an alternative tothis method I suggestadjusting the platevolts of the shieldedvalve to flatten thetuning; a little less

+80

Fig. 6.-Screened-grid valve coupled by fixed -tune transformer withvariable voltage arrangement on plate

of tuning with very high ampli-fication; but on the short-range band,a practical limit is fixed by the valvecapacity below which it is not possibleto go.

0C> EmsK:>

those aperiodic transformers so as toraise the possible magnification pervalve and some years ago I made uprr any sets of a semi-aperiodic type, tun-ing by primitive variometer methods.

Sliding Iron CoreOne such scheme

+80

Fig. 7.-Screened-grid valve coupled by fixed -tune choke, capacity coupledto next valve. Tuning can either be flattened by adjusting plate voltage

of first valve or by having a low value of R

efficient waywould be to shunt the inductancewith a low resistance which couldactually be the leak used in the net-work-and then the shielded valvescan be used at the normal highvalues of M.

This method does not lend itselfto a simple continuous adjustmentwhich the first method does.

Use of Resistance WireA third method which I have used

extensively is to wind the inductancewith resistance wire, but this methodis not too easy to handle exceptprofessionally in standardised gear.

It will easily be seen that stillmore acceptable results could beobtained by getting still greatervalues of L and on the long-rangebroadcast band there is no diffi-culty whatever in obtaining flatness

Aperiodic amplification on veryshort waves, such as the zo-6o metreband is, at the moment, difficult. Iam rather in favour of an attempt touse some crude method of tuning in

consisted in slidingin and out of theinductance an ironcore, made of finelydivided (chemical)iron mixed up withparaffin wax. I also

+80 used a tube of coppersliding in and out ofthe inductance.

The tuning is soflat that several ofthese rough -tuningdevices in the separ-ate styles can be

coupled together if necessary; nogreat accuracy being required.

I[ Another Capt. Round article 1Next Month

An Efficient Frame AerialFRAME aerials on portable sets

usually suffer from the fact thatthey are too small to be properlyefficient. Compactness is essential ina portable, and much is sacrificed tothis end.

For use with " transportables,"and with experimental sets used in-doors, where compactness is not anecessity, a frame aerial benefitsby being quite large.

A really efficient pick-up can be

43

obtained with a frame having sides4 ft. in length, and it is interesting tonote that a frame having these dimen-sions, and with six turns of wirespaced about Y4 in., has a naturalwavelength of 175 metres.

This is not too large a value forgeneral-purpose receiving, and thefact that the sides of the frame arelarge makes it a very useful accessoryfor sets having one or two stages ofH.F. E.D.H.


ate ake Btaa?

Wrong way to hold a valve

THE valve buster that I can claimto know most intimately is my-

self, though, after duly touchingwood, crossing my fingers, and doingall the other things generally held tobe necessary in such circumstances, Ican claim that it is quite a long timesince any fit of temporary insanityon my part led to the untimelydemise of a perfectly good valve.

However, the last time that I wasguilty of anything of the kind I didthings on the grand scale, blowing upfive valves all at once. It happenedduring the period when it was fashion-able for some queer reason to connectH.T. and L.T. batteries in series in-stead of negative to negative.

Setting Matters Right!I noticed that some small compon-

ent or other was not very tightlyfixed to the baseboard and proceededto set matters right with a long -bladed screwdriver. The connectionsin that particular set were made withbare wire, and for an instant theblade happened to touch H.T.positive and L.T. negative. Therewas a blue flame and that was that.

The moral of this touching storyis two -fold. In the first place dis-connect your batteries before youstart prodding into the entrails of theset with any metal tool and secondlyalways connect the batteries inopposition and not in series. There

By R. W. HALLOWSis absolutely no point in connectingthem up in series, for if you do so ashort is almost certain to lead to valvebusting on a scale depending uponthe size of the set.

Should yours happen to be a super -het and you insist on making yourconnections in this way, you may livefor one glorious or inglorious momentat the rate of about ten millionpounds a year.

An Absent-minded FriendAn absent-minded friend per-

formed quite a good valve -bustingact only a few days ago. His batterieswere properly wired, but he managedfor all that to burn out four valves ata blow. How did he do it? Wellhere is the story-a perfectly trueone.

Having wired up the set he foundthat there was a small fault some-where so he disconnected it fromaerial, earth, and batteries, placedit on his workshop bench and decidedto go over it with a galvanometerto see whether he could find the shortwhich apparently existed. There wasan old high-tension battery lyingon the table which still showed about3o volts out of its original 6o. Justthe thing for the job, says he to him-self, say he.

Having tried the battery plus thegalvanometer across the H.T. ter-minals and obtained negative resultsit occurred to him that possibly theremight be a disconnection in the fila-ment circuit. He connected thebattery to the L.T. terminals. Foursimultaneous blue flames showed him(a) that there was no disconnectionand (b), that absentmindedness doesnot pay when conducting tests upona wireless set.

Skeleton Valve HoldersA second friend is very fond of

valve holders of the " skeletonest " ofskeleton types. He generally makeshis own, soldering the four valve legsto strips of brass and fixing the latterto suitable points round the rim of abig circle cut out in a square piece ofebonite. These valve holders are

44

Correct method of gripping valve

the jolliest things in the world so longas you don't try to change valves withthe set in a dark corner and withoutpulling out the H.T. wander plugs.

On a recent evening I remarked tothis friend that the one crab to thissort of valve holder was the ease withwhich a filament -destroying shortcould be made. He assured me thatsuch a thing was utterly impossibleif one only took a reasonable amountof care.

The Vanishing Trick"All you have got to do," said he,

"is this." He pulled a valve out of itsholder, held it between his thumband forefinger, like a conjurer aboutto perform a vanishing trick, andthen stuffed it back again. Therewas quite a nice little flame for hehad touched the plate and filamentnegative legs with the two filamentpins. The moral?

If you use these holders flick outthe wander plugs before you changevalves, or, at any rate, use a pocketflashlamp to throw light in darkplaces.

Friend number three is the kind offellow who is always making neatlittle gadgets. He keeps, as arule, a fairly large stock of valvesand it occurred to him some time agothat it would be awfully handy tomake a stand in which his sparescould be kept. " Some people keep

'em rolling about on the table," hesaid, " and that of course, is simplyasking for trouble. Just look at thisnice little stand I've made. Youwill see that they are as safe ashouses."

What he had done was to make anumber of holes in a piece of ply-wood. This had legs at each of itsfour corners and the valves satcomfortably in the holes just as eggssit in egg cups.

That Spring Clean ... !He was delighted with his stand

until during his absence one day hisbetter -half thought that his den wouldbe the better for a spring-clean.Somebody dropped the stand . . .

The moral of this episode is : Don'tput your eggs all in one basket.

Then there is Blinkinfiatt, who hasmore trouble with his valves than allthe rest of my wireless friends puttogether. He is always beingbothered by noisiness in his receivingset and finding it impossible to tracethe cause. Also valves have what hecalls an uncanny way of coming topieces in his hands He showed meone just the other day, which hadresolved itself into two separate anddistinct parts. One of these was thebulb with a few forlorn wires pro-truding from it; the other was thecap with its pins.

Blinkinfiatt, you see, is one of thosepeople who find that the bulb of avalve fits so nicely into their handsthat they always grasp it firmly whenpressure has to be exercised by re-moving a valve from its holder. Itis not of the slightest use telling himthat the proper place for one's fingerswhen a valve is being withdrawn fromits holder is upon the cap.

One A MonthIf you do so he tells you at once

that he once got a shock by touchingthe plate and filament pins with hisfingers in the process. He main-tains that the bulbs of modern valvesare not properly glued into their capsand that it is the makers' fault andnot his if they come unstuck when hepulls them out. Since he does invalves at the rate of about one amonth he must be a sheer joy to thevalve manufacturer.

Actually few bulbs come straightout of their caps at the first pull.What happens is that he graduallyloosens them and breaks one lead- inthe process. When this has beendone he complains on the calmest of

Wireless Magazine, August, 1928

nights that_ atmospherics are tooappalling for words. The moralhere is too obvious to be mentioned.

Pottlethwaite holds that most of usfiddle about too much with filamentpotentials. All that you need, hemaintains, is a fixed resistor for eachvalve and you need not worry anymore about it. There is somethingin this idea if only you use theright fixed resistors. Pottlethwaite,though, does not care two hootswhether a valve needs 5.5 volts andpasses .25 ampere or is intended toeat ampere at the same potential.

The result is that he is alwaysfinding that valves of his' behavedisgracefully by losing their emissionlong before they should. If youoverrun a dull-eihitter valve you canvery soon turn it into a bright -emitter. Moral? If you use fixedresistors, use 'em sensibly.

Gubbson is all for employing thelowest possible filament potential."Cut down the amps," he says," and your valves will last for ever."Somehow his don't. His filamentslast for ever, but far too early in theircareers they cease to do really usefulwork. He does not realise that thethoriated filament if worked at toolow a potential soon has a surface ofpure tungsten without the desirableadmixture of thoria. The moralhere is that when the makers givefigures they generally know what theyare talking about.

MS.

THAT INTERFERING"LOCAL"

Dear reader, please have pity onA poor, benighted man,

While 1 recite a ditty onThe troubles of a `Van"

Each night whene'er I listen lateTo music (bands and vocal)

From foreign lands, I can't abateThat interfering "local."

I've tried my best to butt it out(A hopeless occupation),

But dashed if I can cut it out,That rude, ill-mannered station

I've a neutrodyne well wired, sir,I've an Armstrong supersonic,

I've got wave -traps (bought and hired,sir),

But the trouble still is chronic.

Will nobody relieve meFrom this troublesome affair

I'd give anything, believe me,Just to push it off the air.Think I'll have to build a station

In the middle of the town,And in utter desperation

Shout the horrid beggar down !C. P. P.

45

RadioMusic

RevivalsSOME hundreds of our songs would

not only be dead by now were itnot for radio, they would have beencompletely forgotten. Radio, andradio only, has kept them alive. Itis true that the gramophone hashelped us to retain some of thesesongs in the memory, but radio has amuch larger repertoire. It is noexaggeration to say that radio haslengthened the average popular songby five years. Indeed, many of themodern foxtrots would have beenstill -born without radio.

When We Were BoysWhen a boy, "We're all single by

the sea," was the favourite song thatwas sung by everybody everywhere.Were it not for radio that song wouldhave been dead to me years ago." Dolly Grey" is another song thathas been revived by wireless. Thepopular songs sung during the GreatWar have been kept going by noother medium as much as wireless.

There does not seem to be anyappreciable revival in literary mattersthrough this medium. What there isis out of all proportion to that ofmusic. The average listener does notknow more of Kipling or Browningthrough radio, although he may bemore acquainted with the playwrightsbecause of the loud -speaker.

Acquainted with the MastersWe are becoming acquainted in-

creasingly with the subtleties of Bach,Beethoven, and the other masters inmusic every week. One wonderswhat would have happened to manyof the works of these geniuses if wewere allowed to develop along musicallines as we were before the adventof radio. One wonders, more, whetherthe ordinary listener would everhave heard many of the greatestmusical works apart from radio.

Whatever radio has done in art,literature, mechanics, hygiene, andhousecraft, we are sure it has givento music the greatest revival of alltimes. Music is having its true placein the life of to -day and that throughthe medium of wireless. E. B. R.

Wireless Magazine. August., 1928

What RedderslinighSetsQ -COIL TWO

CONSISTING of a detector and one-1 stage of transformer -coupled low -fre-quency amplification, the Q -coil Two(WIRELESS MAGAZINE, April, 1928) rt.ceives on both wavelength ranges withoutchanging coils. Its good performance isdescribed below by a Yorkshire reader :

I feel that I must write and congratu-late you on the magnificent performanceof the Q -coil Two. I hooked up this setabout a fortnight ago, and, althoughYork is a notoriously bad position forreceiving broadcast, yet I have alreadyreceived the following stations, thosebeing marked with an asterisk on theloud -speaker, the rest being on phones :

Long Waves.-Huizen, Moscow*, Ka-lundborg*, Leningrad, Radio -Paris,Konigswusterhausen, Warsaw, 5XX*,Boden, Hilversum*.

Short Waves.-5GB*, Reval, Man-chester*, Berlin (Voxhaus)*, Bilbao*,Cardiff*, Bern*, Stuttgart*, Huizen,Copenhagen, Newcastle*, Leeds*, PetitParisien*, Belfast*, Sheffield*, Breslau*,Cologne, Glasgow.

Total on loud -speaker, 18.Additional on phones, ro.This gives a total of 28 stations, and

I have no doubt that there are manymore that I can manage to get yet.

GIRDLE TWOrROM all parts of the world we are still1. receiving splendid reports of the GirdleTwo (WIRELESS MAGAZINE, September,1927). As this issue is now almost out ofprint, we would point out that the Crusader(May, 1928) is a similar type of set andshould give equally good results. Here is aNew Zealand reader's experience of theGirdle Two :

From time to time I notice in yourjournal reports from readers who havemade up various sets. Some time agoI wrote telling you of the success ob-tained with the Girdle Two in this cornerof the world.

As a regular reader, I have not noticedany reports from Australia and NewZealand. However good previous re-ports on the Girdle Two have been, Ithink the following log will convince youthe set is worthy of its name :

New Zealand : 2AT, 2AQ, zAL, 2AP,2AW, 2CO, 2B0, zBI, 2AB, 2BH, zXA,2AI, 2BA, 3AU, 3AP, 3A J, 3AL, 3AR,3AH, 4AM. Australia : 2FC, zSS, 3L0,6AG. Russia : RFM. Japan : AV.America: 2FAL, 2XG, 2 M.F (2 XAFrelayed WFBL, WGY, WMAK, andWHAM). South America : RCB8.Holland : PCJ J. England : 5SW.

Using three valves, zXAF, 2FC, 3L0,PCJ J, 5SW, and RFM came through onthe loud -speaker. 5SW was the onlystation that was really weak on the loud-speaker. In fact, it was more distinct onthe phones with two valves.

In every case the announcement andcall of each station was heard distinctly.

and the only trouble experienced waswhen I tried 5SW on the loud -speaker.For some reason the set howled before itwas correctly tuned, and rather thanhave weak signals, I went back to thephones.

In tuning, I find several dead spots, butI have never regretted building the set,as it is far ahead of other short-wavesets I have heard.

FIVE SETS IN SIX MONTHS !

BELOW we reproduce portions of a letterfrom a reader in Co. Wicklow, who has

built five " W .M." sets since Christmas.These were the Five -guinea Three (WIRE-LESS MAGAZINE, November, 1927), theTrapped Three -Four (March, 1928), the

WONT YOU LET US

KNOW WHAT RESULTSYOU ARE GETTING WITHYOUR " W.M." SET ? ANYKIND CF REPORT IS HELP-FUL TO OTHER READERS-THE OPINIONS REPRO-DUCED HERE MAY HELPYOU TO DECIDE WHICH

SET TO BUILD NEXT !

Everyday Three (February, 1928), theBritannia Three (April, 1928), and theCrusader (May, 1928). We have not hadany adverse reports of the Everyday Threeor the Britannia Three from any otherreader :

Having now constructed five of yourvalve sets since last Christmas, I thoughtI would write and let you know myexperience of them. First of all, beforethis I had never even tuned -in a valveset, having used only a crystal set withamplifier.

I began with the Five -guinea Three,and got seventeen stations in oneevening, fifteen at loud -speakerstrength.

My next effort was the Trapped Three -Four, built with the standard R.I. tuner,instead of R.I. & Varlet' type B as laiddown in list of components. I found Ihad, however, to use a wavetrap to pre-vent local station (Dublin, fourteen milesaway) disturbance, and built the trapdescribed on page 246 of your October,1927, number, which works excellently.The tone and volume of this set are veryfine, and I have had excellent results,especially on Daventry (5XX) wave-band, getting 5 XX, Konigswusterhausen,Kalundborg (especially loud), Paris (bothRadio and Eiffel Tower), as well asMotala. Hilversum, and another station,

46

not yet identified, but which I believeto be Warsaw, came through, but notso well.

I get a good number of broadcastwaveband stations, but curiously enoughhave not yet succeeded in getting 5GBon this set I

I next built the Everyday Threeand the Britannia Three, but Iscrapped both these, as I found themvery unstable and non -selective, al-though of fair volume.

My last effort was the Crusader, andpersonally I can't imagine a better two-valver. Last night I had sixteen stationson this set, mostly on the broadcastwaveband; 5GB is particularly good.The phone strength is so good that moststations, including Budapest, can beheard on loud -speaker I

I tried the short waves one night, andgot zKAD, relaying Schenectady, atabout 12.3o a.m. I could hear the base-ball scores quite plainly and music later,although atmospherics were bad. Mywife, who had gone upstairs to bed,could actually hear the music throughthe loud -speaker, though, of course,rather faintly.

5GB is particularly good in this set,and so far hasn't faded by day or night,a fault generally found here in Irelandwith this station. It is so bad on myFive -guinea Three that sometimes Ialmost lose this station, while at othertimes it is roaring through I

In conclusion, may I thank you for yourexcellent magazine ? All instructionsare so clear and the blueprints so easy tofollow. I wait anxiously for the twenty-fifth of the month and my new copy.

THE CRUSADERNOBODY who builds up the Crusader

(WIRELESS MAGAZINE, May, 1928)will be disappointed with it. The resultsobtained with two valves are really excel-lent, as this letter from a Sheffield readerproves :

I feel I must write to say whatremarkable results I have obtained fromthe Crusader, the most outstanding fea-ture being the absence of hand -capacityon the short waves.

The following short-wave stationshave been logged : WGY, 2 XAF, 7RL(on loud -speaker), PC J J (on loud-speaker), AFK (on loud -speaker), andyesterday morning 3L0 Melbourne.Speech was particularly good.

Dozens of amateurs can easily betuned in by the beginner, another pointbeing that this set can be made frommany old parts.

On the long and broadcast bandsresults are all that can be desired, andmany stations will give real loud -speakerresults, even in a district like Sheffield.

I advise anyone having spare parts intheir "junk" box to get them out andput this set together; they will beastounded at the results.

GRAMO-RADIO SECTION Wireless Magazine. August. 1928

"WirelessMagazin

GRAMO-

RADIOSECTION

" STARTING OFF ""CAN you play anything ? "

queries a fair admirer." Rather," says the blonde -pre-

ferring gentleman. "I play thegramophone quite well." (Chucklesof laughter from the fair admirer,which modulate into a jazzy tune asthe B. -P. G. puts on a record of thelatest swamp noises.)

As a matter of fact, I would quitelike to bet on the fact that althoughthe B. -P. G. plays the gramophoneand pick-up equipment well enoughto allow him to dance with the F. A.,he does not play the gramophoneproperly. Few people take thetrouble to do so.

Here is a test of knowledge, if notof skill. Most people, nine of everyten, perhaps, set the turn -tablerevolving, giving it a good startwith a greasy finger rotated on therecord face, and then drop the pick-up needle once or twice on the edgeto see if that is the " start." Oftenas not it isn't, and several snatchesof melody are heard before the itemstarts properly.

Then the lid is closed, and the"performer" settles back in corn..fort, or dances, confident that thatis the be-all and end-all of gramo-phone manipulation.

If the cap fits, wear it. It is notadvisable to speed up the turn -table,in the case of most motor units;fingers should never be placed onthe record face, anyway. Mostimportant, though, is the fact thata pick-up or sound -box shouldnever be dropped on a record. Theneedle should be allowed to rest onthe outside plain edge of the recordand pushed in with the forefingeruntil the needle point engages withthe sound grooves. QUEUE.

" FAKING " THE CURVETHE low -frequency equipment

of a gramophone amplifier pro-vides ample scope for experinamintingwith values of various L.F. com-ponents. The kind of alterationthat will chiefly be made is in thenatural pitch range of the amplifier.

Trying out thenew Lissenolaportable gramo-phone, which isexcellent value

for money

Maybe the pick-up itself does notgive very even amplification, or,if transformer coupling is used inthe amplifier, the iron cores of thetransformers may be distorting.

It is always better, when possible,to remedy the trouble at its source.But, even when possible, this is notalways easy. It is difficult toarrange the L.F. side of a medium -power receiver so that amplificationis constant over a wide frequencyrange; the difficulties are muchgreater in gramophone amplifiers,where the grid -swings are largeand an equally broad frequencyband has to be covered evenly.

Nevertheless the amplificationcurve may be faked to accentuatethe higher or the lower of audio fre-quencies, so making up for defects inother components.

A fairly small fixed condenserplaced across the secondary ,of thecoupling transformer will attenuatethe high frequencies, while an L.F.choke across the primary will alterthe low frequencies. B.

IS THERE ANYTHING SPECIAL YOU WANT TO KNOWABOUT GRAMO-RADIO ?

Whatever you want to know about Gramo-Radio,consult the " Wireless Magazine " Technical Staff.For many months they have kept abreast of this latestdevelopment and can reply to any query that may beraised in connection with it.

If your pick-up does not give the results you think itshould-if your amplifier is not quite distortionless-in fact, if you are in trouble of any sort, the TechnicalStaff can put you on the right track.

So that the Staff is not absolutely overwhelmed with

queries (and to avoid the trouble of answering any of afrivolous nature, which results from a free service)a nominal fee of 1 s. is charged for each questionasked.

Write your query or queries (not more than two can beanswered for each reader) on one side of a sheet of paperand send it, together with a stamped addressed envelope,a postal order for 1 s. and the coupon from page iii of thecover, to Gramo-Radio Queries," Wireless Magazine,"58/61, Fetter Lane, R.C.4;

47

Wireless Magazine. August. 19281 CRAMO-RADIO SECTION

FickupAngle andWeight: trY,°eucrts?By H. T. BARNETT, who in the June issue of the" Wireless Magazine" discussed gramophone motors, thecentration of records on turn -tables, the prevention of skidding

and the correction of faulty needle -track alignment

Dubilier electrostatic pick-up

rr HE month before last, in refer-ence' to the primary factors

necessary for playing gramophonerecords so as to get the best results,no matter whether the amplifica-tion be mechanical or electrical; weconsidered motors, centration ofrecords and needle -track align-ment.

The last subject named is by farthe most important thing in gramo-phone science, so that new readerswho have not perused this articleshould at once take steps to do so.(It appeared on page 46o of the Juneissue of the WIRELESS MAGAZINE.)

STYLUS -BAR ANGLE ORNEEDLE ANGLE

On the majority of gramophonessold to -day the angle at which thestylus bar (and consequently theneedle) is set to the horizontal is6o°. This is the angle made by thehour hand of a clock at 7 o'clock.The re-entrant H.M.V. machineshave the sound boxes set so that theneedle is at an angle slightly moresteep than this.

Angles Less Than SixtyDegrees

Many machines now have theneedle angle arranged to be lesssteep than 60°. I can name several .

in which the needle angle of 500(corresponding to the position ofthe hour hand of a clock at twentypast seven) that I have continuallyrecommended for electric record-ings has been adopted.

For fibre needles, and for thoseonly, the angle of 600 is correctbecause the points are so cut thatwhen the needle is placed in a stylusbar at 600 angle, then the actualpoint of the needle is vertical, whichis its necessary position.

Fifty Degrees PreferableFor steel needles, and especially

for fine -gauge steel needles, whetherof the soft -toned variety or thoseloud -toned needles held in grips oradaptors, I much prefer the workingangle to be 500, because in the firstplace surface noise is much less;secondly, the records do not tend towear so rapidly; and, thirdly, owingto the diminished jarring and jump-ing on surface flaws and on heavywave form, the average quality ofdefinition is greatly improved.

It is quite an easy thing to tryout this matter of needle angle, andanyone who feels doubt whetherperfection of reproduction will sufferas regards cleanness of outline andinstrittnental characteristic shouldhe adopt the angle giving reducedsurface noise and reduced wear onrecords, should experiment for him-self on all kinds of records, newand old.

Changing Needle AngleIt is important, in changing from

one needle angle to another, thatone should look to the needle -trackalignment to see that it has not beenprejudiced by the change. The samecare is needed should one change thesound -box diameter or the length ofthe needle one is using.

Needle -track alignment shouldnot be permanently adjusted untilone has finally determined what

Amplion Vivavox pick-up

needle angle, what kind of soundbox or pick-up, and what needlesare to be used. The last adjustmentis best made in the case of agramophone by shifting the motorback or forward a little, but in usinga pick-up with a gramophone motor,and tone arm mounted perhaps on asoap box, it will be easier to shiftthe tone arm.

Less Surface NoiseThe fact that a 5o° angle gives

less surface noise than 6o° in itselfproves that it is better for the life ofthe records because at the moresloping angle there is a greater sur-face of the needle in contact withthe record, so that reduced scratchunder these adverse surface contactarea conditions is a quite certainindication of greatly reduced dig-ging effect.

Taking the pattern from a seg-ment of your clock face, you caneasily cut a triangle of cardboard toset your stylus bar to, should youreye not naturally be accurateenough for the purpose.

NEEDLE CANTSome stylus bars are not at right

angles to the sound box or pick-upneck axis. Some swivel -neck tonearms are not properly set on the

48

CRAMO-RADIO SECTION Wireless Magazine. August. 1928

motor board in relation to theheight of the turn -table and thediameter of the sound -box and thelength of the needle. The result ineither case may cant the needletowards one side or the other of thegroove.

I have never found a slight degreeof cant cause any trouble whenusing fine -gauge steel grip needles,but obviously it should not be ap-preciable, for surface noise reasonsif for no others. When the point ofsuch a needle is bearing in theextreme bottom of the " V " groove,the surface noise is demonstrablyless than when the needle is cantedso that perhaps all one side of it isin contact with one side of thegroove.

Final AdjustmentFinal adjustment can sometimes

be got by putting a spare record ortwo under the non-skid mat on theturn -table. If raising the tone armby washers under its base is neces-sary, great care should be taken inthe case of a gramophone to makethe centre or tone hole through thewasher exactly the size of the inter-nal base diameter of the tone arm.

WEIGHT ON NEEDLEIn nearly all machines the weight

on the needle is very excessive.Makers of gramophones having asteep needle angle have had to pileon weight in order to prevent theneedle from jumping right out of thegroove when it comes to an obstruc-tion or roughness. Of course theeffect is to cause the needle to tearthe record surface instead of jump-ing the obstruction.

Almost by every post I get lettersfrom people who have boughtexpensive modern machines, manyof them having correct track align-ment, unfortunate people who findtheir new records tear up in a fewplayings ; they are at their wit's endto fathom the cause of the trouble.

Excessive WeightWhere the track alignment is

good and the needle angle is 5o°, thecause of the difficulty is almostinvariably excessive weight on theneedle. Bad needles may cause thetrouble, even when. everything elseis right, but in nine cases out of tenthe fault lies in the excessiveweighting and not in the kind ofneedle chosen.

So far as my experience goes, bothfibre needles and fine -gauge steelgrip needles work best with fromtwo to four ounces weight on theneedle. For ordinary needles theweight should not exceed fiveounces. Of course I am presuppos-ing correct reproducing conditionsin other respects.

People sometimes ask me howthey can tell what weight theirmachine puts on the needle. Inorder to find this out, a friend ofmine got a piece of his wife's elastic.He tied a piece of string on one end,tied the string round the neck ofthe tone arm, and then raised thesound -box from the record bystretching the elastic upwardly. Hemeasured the length of the elasticwhen stretched. Then, with anenvelope and some bits of card, heweighted the elastic to the sameextension and took the envelopeand its contents to the post officeand had it weighed !

TWO FINE GRAM&RADIO SETS AREDESCRIBED ON OTHERPAGES OF THIS ISSUE-THE CONNOISSEUR'SSIX (PAGE 20) Eg' THEGLEE -SINGER THREE

(PAGE 55)

Means by which one may decreasethe weight on the needle are many.I prefer an absolutely dead weightdirectly fastened in the case of one-piece tone arms to the back of thetone arm itself, and in the case ofswivel -end tone arms to the oppositeside of the swivel from the sound -box and close up to the swivelpoint.

In my Peridulce, and with theColumbia type of tone arm gener-ally, about a pound and a half oflead made into a weight capable oflying close to the back of the tonearm base works wonders.

This not only counter -balancesthe tone arm so that only the weightof the sound -box comes on to therecord, but its weight right over thetone arm base keeps the tone armbase bearing down to its job (anyrattle here rapidly ruins records),but also its mass opposes movementof the tone arm as a whole by theneedle and increases the amount ofthe motion of the needle communi-

cated to the diaphragm, therebyincreasing tone volume and im-proving definition.

For swivel -end tone arms from6 oz. to 12 oz. of lead should befixed on the swivelling portion closeup to the swivel joint and on theopposite side of it to the sound -box.The weight required will depend onthe weight of the swivel end and itsleverage.

Making Your Own WeightIf you cannot get the weight de-

sired cast to shape for you andnicely plated; it is easy to make sucha weight by rolling up a strip ofroofing lead, and such a weight isvery easily hammered into anydesired shape. Lead is at all timesvery ductile, and especially so whenin coiled strip.

In the case of swivel -end tonearms, as well as with the straightpattern kind, the dead-weight coun-ter -balance has two useful functionsin addition tolessening weight on theneedle; it keeps the tone -arm jointsfrom rattling and, by its weight,opposed to needle vibration andsituated right behind the sound -box, increases tone volume andimproves definition.

For ExperimentersExperimental people often prefer

to sacrifice the two extra advan-tages of the fixed dead-weight de-vice in order to have the counter-balance adjustable for experimentswith different kinds of needles. Asound -box will shortly be marketedby the Limit Engineering Co., Ltd.,of 17 Albion Street, London, N.',that incorporates its own weightadjuster. This will not be applic-able to magnetic pick-ups however.

There is a castor trolley wheelthat runs on the record and carriesa spring (having a screw adjust-ment) that presses the sound -boxupwards.

For tone arms of the H.M.V. typean excellent adjustable leveragedevice is marketed by H. L. Wilson,of 245 Shaftesbury Avenue, W.C.The actual counterweight worksthrough a pivoted lever on one endof which it may be slid and clampedin any desired position.

ADHESIONBefore going on to the subject of

needles, considered particularly inreference to the wear they produce

49

Wireless Magazine. August, 1928GRAMO-RADIO SECTION

Pick-up Angle and Weight : Are Yours Correct ? (Continued)

Weight adjuster for swivel -end tone arms,made by Cramp tons

on records, it is necessary to con-sider the chief factor producingfrictional wear.

Fine -gauge NeedlesMy advocacy for the use of fine -

gauge steel needles made of exceed-ingly hard metal (it is essential thatit should be tempered so as to betough as well as hard) has often ledto the query : " But surely thesevery sharp needles must wear arecord more than the ordi-nary steel needles do? "

Such is not the case; theharder the steel and thesharper the point the lessthe record will wear, assum-ing of course that theneedle is lying in the grooveon a fore and aft line thatis a tangent to the circle, that ithas a reasonable inclination-say30°-and that there is not too muchweight put upon it.

If this were not the case, weshould play our records with needlesmade of copper or brass or some-thing of that kind.Wear Re -acts

The whole question resolves itselfin one of adhesion. If the needleadheres to the record, the needlewill wear and the record will weartoo ; if the needle is too hard and itsstructure not sufficiently crystallineto permit it to adhere to the record,then the wear on the needle will bevery small and the record will notwear at all, but will burnish.

If an engineer has a steel shaft torotate and wishes to avoid wearupon it, he does not mount it insteel bearings, but in bronze orwhite metal, for the reason that asteel shaft and a steel bearing hav-ing the same internal structure tend

to adhere to oneanother, but steeland bronze, or,better still, steeland white metal,having differentinternal struc-tures,thetendencyto adhesion andconsequently towear is greatlylessened.

A glass workerdesiring to make a

hole through a glass plate does nottry to pierce it with a steel drill, heuses a copper rod; the copper ad-heres to the glass and engages theglass particles as soon as they aredetached, and so a screw hole mayrapidly be cut through a mirror orwhatever it may be.

Our stone -age forefathers, when

Another weightadjuster, madeby H. L. Wilson

they wished to shape their arrow-heads from flints, did not use ahard substance for the purpose,they used chisels of reindeer bone;the bone adhered to the flint andbrought it away in flakes so easilythat a man could make hundreds ofarrow -heads in a day.

Burnishers for use on metal aremade of agate, the hardest materialcommonly obtainable. So long astoo much weight is not put uponthem they do not scratch the metal,but produce abeautiful polishupon it.

ANOTHERWEIGHT

ADJUSTERSince writing

the above, I havereceived from themanufacturers,Cramptons, 346Denman Street,Radford, Notting-

ham, a sample of their Castle weightadjuster for swivel -end tone arms.

Leverage TypeIt will be seen that it is of the

leverage type, the fulcrum clampingon to the tone arm proper, with arubber -lined clip very like a cycleclip. The end of the lever having alittle bit of rubber tube on it, restsunder the swivel end of the tonearm and tends to reduce the weighton the needle in proportion as thesliding weight on the other end ofthe lever is moved farther awayfrom the fulcrum.

N.B.-Should the matter of thisor of any subsequent article beunclear to any reader, I shall bepleased to reply personally toany inquiries addressed to me atthe offices of the WIRELESSMAGAZINE, if complying with therules outlined on page 47.

LissenPortable

GramophonesTWO new portable gramophones

which are both excellent valuefor money have just been placed onthe market by Lissen, Ltd., ofFriars Lane, Richmond, Surrey.

The smaller model, known as theLissenola No. r, costs only twoguineas. One of these is in constantuse in the WIRW,ESS MAGAZINEConstructional Dept., and is givingvery satisfactory results; it is illus-trated on the first page of this sec-tion. This model is fitted with aThorens motor.

The other model, the LissenolaNo. 4, is slightly more expensiveand is fitted with a Garrard motor.

Weight adjuster fixed at base of tone arm whichincreases tone volume and improves definition

50

GRAMO-RADIO SECTION Wireless Magazine. August. 1928

An Outline ofiGramophone Developments

The first part of this article appeared on page 536 of the July issueTHE comparatively new method

of playing records electrically isof considerable interest to thewireless amateur, as it enables himto use his receiver in a doublecapacity. If the receiver is capableof giving good quality reproductionfrom a modern cone loud -speaker,the owner should obtain resultsequal to those heard from the mostexpensive mechanical gramophone.And in some respects the resultswill be superior.

Good ComponentsThis is assuming that he is

using a super -power valve forthe output and plenty of H.T.,and that the low -frequencypart of the set consists of thepopular combination of resist-ance -capacity and transformer,using only the best components.

On the other hand, if theamateur constructs a well -designed amplifier to be usedwith valves having the correctcharacteristics for the job andoperates a moving -coil loud-speaker, he will obtain resultsthat no mechanical gramophonecan ever give. Electrical repro-duction hz s the further advant-age over the mechanical methodin that the listener has completecontrol over the volume, itbeing possible to obtain any-thing from a whisper to full volumewithout changing the needle andwhile the record is being played.

Great Boon to DancersDancers find the electrical method

an advantage because, by placing .aloud -speaker in several parts of ahouse, it obviates the necessity forthem to crowd into one room tohear the music.

The gramophone pick-up, whichmakes possible the playing ofrecords electrically, usually operates

on electro-magnetic principles. Theneedle is screwed into an iron reedwhich is in the centre of a bobbin offine wire and between the poles of apermanent magnet. The vibrationspicked up from the record by theneedle cause the reed to vibratelikewise, many thousands of timesa second, thus cutting the lines offorce between the poles of the mag-net and generating small electrical

Playing desk unit of the His Master'sVoice electrical reproducer. It ismade by the Gramophone Co., Ltd.,

of Hayes, Middlesex.

impulses in the pick-up coil.These impulses are fed to the

input of the amplifier and, afterbeing amplified, are converted intoaudible sound by the loud -speaker.

On the mechanical gramophone agreat deal of the brilliance of arecord is lost because many of thesmall sound waves on a recordwhich constitute the "light andshade " of the music have notsufficient amplitude to be madeaudible. In other words, the needlevibrations are too small for the

sound -box to convert them into airwaves.

The pick-up, however, is sensitiveenough to respond to them and somany of them become audible.Thus, although a good receiver mayhave a musical range no greaterthan that of a modern gramophone,a record will sound more brilliantbecause of the better reproductionof the weaker sound waves.

up,loud -speaker.

Advanced Design of Pick-upThe pick-up is of advanced

design. The poles of the magneticfield face a small steel diaphragm towhich the needle -holder is attached.A heavy permanent magnet pro-vides the necessary flux across thegap in front of the poles. The damp-ing is provided by oil of the correctviscosity circulating between themagnetic poles, this being far

ManufacturersSince the electrical repro-

ducer has certain advantagesover the ordinary gramophone,it is only natural that the manu-facturers should turn theirattention to this new develop-ment.

The latest commercial pro-duct is the His Master's Voiceelectrical reproducer, designedfor use in cinemas, etc. It givesout tremendous volume with-out a trace of distortion and isparticularly good on organrecords. It is doubtful if acinema audience could tell thedifference between a record andthe actual organ, especially ifthe record is of that particularorgan.

The H.M.V. reproducer con-sists of three main units-theplaying desk, on which ismounted the motor and pick -

the amplifier, and the

51

Wireless Magazine. August.. .1928 GRAMO-RADIO SECTION

An Outline of Gramophone Developments (Continued)more satisfactory than the usualsystem of rubber damping. Thediaphragm, which is not more than1,, th of an inch thick, is gold-

plated to prevent corrosion.Correct pressure on the record is

obtained by pivoting the pick-up, acounter weight being concealed inthe tone -arm. The pick-up is lowresistance wound, so long leads canbe used to the amplifier without thecapacity having any effect on thequality. The amplifier is A.C. mainsoperated, suitably rectified, nobatteries being required.

Two -stage AmplifierIf the mains are D.C. a motor is

used to provide the A.C. power.The amplifier is a two -stage ampli-fier with a modified push-pullcoupling. Induction noises areprevented by earthing the centretap on the input transformerprimary, the secondary being con-nected to the grid of a special yalve.Precautions* are taken to preventparasitic oscillation in the amplifier.

Osram valves, type DETI, arefed by the push-pull transformer,the transformer in the anode circuitshaving a centre -tapped outputwinding which is earthed. A low -resistance winding is used so thatthe loud -speaker can be somedistance away without the leadsaffecting the quality of reproductionby undue capacity.

The loud -speaker itself is ofunusual design. The diaphragm isno less than 3o in. in diameter andis of very thin aluminium sheet. Itis clamped between strong alumin-ium rings and is maintained in ataut condition. The drive is amoving -coil of edgewise -woundcopper strip mounted on the dia-phragm at a point removed fromthe centre. A small air gap is pro-vided, across which an intense fieldis created with a consumption ofabout 25 watts.

Baffle Board UnnecessaryThe large diameter of the dia-

phragm makes a baffle boardunnecessary; and owing to its free-dom of movement, it brings out thebass notes in their true value andwithout any sacrifice of the upperregister. The loud -speaker ismounted in a large cabinet with agrille front.

For an ordinary horn -type loud-speaker to have the same musicalrange of this one, it would have tobe about 9 ft. high, 8 ft. wide, 6 ft.deep, and weigh about a ton and ahalf ! It would still, of course,suffer from the defects of the horn -type loud -speaker, such as thedirection effect and its attendantdisadvantages. The H.M.V.electrical reproducer probably givesthe most perfect reproduction ofgramophone records yet attained,and readers should take the firstopportunity of hearing this wonder-ful instrument.

The construction of a valveamplifier to give natural andreliable reproduction is easier whenit is to be used for records thanwhen it is to be used for broad-cast reception. The reason is thatwith the latter there is always therisk of high -frequency currentscreeping in and causing distortion.Further, owing to the varying signalstrength, it is easier for the outputvalve to be overloaded. For recordreproduction, however, there isno H.F. to contend with and theamplifier can be designed so thatthere will be no overloading of thelast valve.

Limited Pick-up InputThis is because a pick-up has a

limited input, no matter how loud arecord may be. If the constructorknows the maximum voltage swingof his pick-up (the best type givesapproximately 3 -volt maximum) hecan then arrange his circuit so thatthe last valve never receives morethan its maximum grid swing.

It is best to use resistance -capacitycoupling throughout for the properreproduction of the bass notes.Low -value anode resistances andmedium -impedance valves shouldbe used, otherwise there will be aserious loss of the high notes.The amplification will not be greatwith two stages, but the quality willbe excellent.

Greater volume can, of course, beobtained with three stages, butsteps must be taken to preventL.F. oscillation. Plenty of H.T.must be used and a super -powervalve is needed for the output.Transformer or choke coupling tothe loud -speaker is essential inthese days of heavyanode potentials.

Good quality components must beused, otherwise the constructor willget plenty of noise but no music !

Do not spoil a good outfit byusing a cheap gramophone motor.When a needle has to track a bigsound wave it tries to act as a breakon the record, and so if the motor isat all weak it will slow down,producing a wail -like note. This is aparticularly unpleasant fault andcompletely spoils good reproduction.It is occasionally the fault of therecord, due to the hole in thedisc not being quite central, but acheap motor is mostly to blame.

Gramophone of the FutureEnough has been said to show the

reader the trend of gramophonedevelopments, and it is hoped hewill have a better idea both of theimprovements in the mechanicalgramophone and of the electricalmethod of reproduction. There isno doubt of the latter's superiorityand the gramophone of the futurewill assuredly be of this type,although the mechanical machinewill remain for many years owing toits simplicity.

Records will probably remain asthey are for some time to come, theimprovements being the elimina-tion of surface noise and a toughen-ing of the composition.

The only disadvantage of thegramophone to -day is the impossi-bility of having a complete opera orsymphony on one record. This maybe overcome by the development ofa "music film." Many readersmust have heard the "Movie -tone"talking film. The music, etc., isrecorded on the film itself in theform of light . rays. These areconverted by a light-sensitive celland valve amplifier back again intothe original sounds and heard bythe audience through loud -speakers.

A Subscription LibraryPossibly records may one day

take this form, and we shall thenbe able to hear our favourite operaWhen we like and without havingto keep changing records. It maybe possible then to join a sub-scription library, just as users of aplayer piano can for the hire ofmusic rolls or the owners of homecinemas for the hire of films.

C. H. GALLOWAY.

52


Specially Garnered by JAY COOTE

POLANDis rapidly coming to the

fore and within the next sixmonths should be in possession ofone of the most up-to-date Europeanbroadcasting systems. By the end ofthis year the Warsaw programme willbe available daily to a greater numberof listeners in the United Kingdomto the same degree as are to -dayKalundborg, Vienna (when not obliter-ated by morse), and Koenigswuster-hausen, for the capital transmitter bythen will be broadcasting its pro-grammes on a power of some 25 kw.in the aerial. Some noise !

A Step in General SchemeThis improvement is but one step

in the general scheme adopted byPolskie Radio for the development ofits system. Posen, which has becomeone of its main stations,will extend itssphere of influence to Bromberg orThorn, both of which cities similarlyto Posen formed part of Prussia beforethe Great War. The new relay, how-ever, in imitation of the German planto be carried out at Flensburg,Magdeburg and Stettin, will work ona wavelength common to the mothertransmitter.

Moreover, as Radio Posnan isanxious that its entertainments shouldbe heard by the many thousands ofits citizens who have emigrated tothe New World a powerful short-wavestation is to be installed in one ofits local theatres.

A New 18 -kw. StationThe new scheme also provides for

an r8 -kilowatt station at Lemberg-of which the native name is Lvov-formerly in Austrian Galicia, now amember of the Polish Republic, andthe Wilno station, of recent birth, isalready to be endowed with newbroadcasting plant, its old equipmentto be transferred to Lodz, the centreof an important industrial district.

For some little time past PolskieRadio has been working actively inco-operation with Berlin and Viennaon a regular interchange of wireless

programmes with these foreigncapitals, the main idea being that eachcity in turn should provide its verybest native talent on these evenings.Warsaw is proud of its Opera Houseand Concert Hall, and from themstar performances are to be relayed.

For your guidance also I may tellyou that the summer and autumnmonths promise pleasant surprisesfrom the Polish studios, as I hearthat Jan Kiepura, the famous tenor,has been engaged for the opera season

THIS IS FRANK ASHWORTHWho broad-casts dancemusic fromthe HotelMetropole

at Posen, from which centre regularlyevery week entertainments are fedto the Polskie Radio system.

With the official opening at Linzof a 500 -watt relay station, " Ravag,"the Austrian broadcasting company,controls six separate transmittersincluding the new Rosenhuegel, nowin perfect working order. Linz, onthe right bank of the Danube inUpper Austria, is but roo miles fromthe capital, but the broadcastingstation fills a long -felt want becausethe city is the centre of a thicklypopulated industrial district.

Within a few months we shall also see a new transmitter at Salzburg, anold-world town situated in the HoheTauern region of the Austrian Alps,

53

some 95 miles E.S.E. of Munich. Itwill act as a connecting link betweenthe Bavarian capital and Vienna, andthrough it passes the special cablewhich is used for the exchange ofprogrammes made by these twocities.

Great Increase in LicencesSeven broadcasting stations for a

comparatively small country such asis now post-war Austria seems a highnumber, but it appears that theirestablishment is justified by thenumber of licence holders. At the be-ginning of 1928 the Ravag possessedsome z8o,000 registered listenersor roughly 4.5 per cent. of the totalpopulation, to -day there are nearly200,000 subscribers in Vienna alone,a figure rep -esenting over one -tenthof the inhabitants of the Austriancapital.

The broadcasting tax is not a fixedone as in most Continental countriesbut variable in proportion to theincome enjoyed by the owner of awireless receiver, the lowest monthlyfee being two Austrian " schellings,"roughly is. 2d. As some well-to-doradio fans might be assessed at thehigher rate of, say, 3 ros.per annum,it has been the custom to register theset as belonging to Baby or to Cook inorder that the concerts may bereceived at the lower fee !

Collected by the PostmanAs in Germany the tax is collects 1

by the postman on his rounds, thePost Office authorities following GreatBritain's lead in pocketing a portionof the proceeds to cover administra-tive expenses-and then some !

Whether the decisions taken at thelast Washington Conference will turnout to our advantage or not will beproved only by practical experience,but by the end of this year there is a strong probability that we shall see acomplete re -shuffle of the wavelengthsallotted to the broadcasting stationsoperating outside and above themiddle broadcasting band


Jay Coote's Continental Notes (Continued)

It is evident that many tests willhave to be made before these stationsget into their proper positions, thatis, if the same kind of interference aspersists at present is not to mar theprogrammes of the high -power trans-mitters.

Seven Countries SatisfiedAt the recent Conference held at

Lausanne by the International Unionof European Broadcasters, the ques-tion was seriously discussed and ofthe fifteen applications received foran allotment in the ether, provision-ally, it was found possible to satisfyonly Great Britain, France, Germany,Holland, Russia, Poland, and Sweden.As to the others, the only prospectoffered was to find them a situationin the already congested broadcastingband.

For the present at least, the sug-gested wavelengths are as follows :Huizen 1,852 m., Radio -Paris,2,752 m., Koenigswusterhausen1,649 m., Daventry 1,561 m., Mos-cow 1,483 m., Warsaw 1,414 m., andMotala 1,352 m. An attempt will bemade, I understand, to treat withRussia with a view to a release of the1,483 m. wavelength to be adjudi-cated to Kalundborg.

The main difficulty consists in thefact that there exists some seventeenstations in all in operation or pro-posed, and that they wish to be fittedin the 1,34o-1,875 metre waveband.It is just this question of the quartand pint pot which adds years to theage of the engineers responsible forcarrying out the Washington pro-posals.

I do not approach the subject in

any spirit of carping criticism, but Icannot help feeling that our B.B.C.shows considerably less initiative thanthe German broadcasting authoritiesin the matter of relaying outsideevents of national interest.

Grand Opportunity LostWhen the seaplaneFriendship, with

the aviator Stultz and Miss Earhartlanded off the coast of Wales, ourhome stations lost a grand oppor-tunity in failing to give us an inter-view at the microphone with theplucky adventurers. Was there anyreason for which it could not havebeen carried out on the spot withina few hours of the historic event?

Through the German stations I wasable to visualise official receptionsgiven to Lindburgh on his return

(Continued on page 61)

ORLDS BROADCASTINGWave- Wave- Wave- Wave-length Call length Call length Call length Call

in Station Sign in Station Sign in Station Sign in Station SignMetres Metres Metres Metres

24 Chelmsford . 5SW 288.5 Edinburgh 2EH 379.7 Stuttgart . 549.3 Milan30 Bergen . . 289.3 Radio Lyon . 384.6 Manchester . 2ZY 555.8 Budapest.30.2 Hilversum . 294.1 Dundee . . 2DE 391 Toulouse. . Hamar -36 Lyon (PTT) . Hull. . . 6KH 394.7 Hamburg . 566 Augsburg37 Vitus (Paris) . Innsbruck 400 Bilbao . . Cracow45.3 Doeberitz . Stoke-on-Trent 5ST Cadiz . . EAJ3 Hamar61 Paris . . Radio LL Swansea . . 5SX Cork . . 6CK 575.8 Freiburg .

Doeberitz . 297 Liverpool 6LV Mont de Marsan 576 Vienna (Wien)558 Beziers . . Radio Agen Plymouth . 5PY 588 Zurich .

192 Akureyri . . Hanover . 4or Aachen . . 68o Lausanne .

198 Biarritz . . 300 Algiers 405 Salamanca EAJ22 720 Ostersund .

204.1 Kaisersleutem Bratislava 405.4 Glasgow . 5SC 76o Geneva . .

257 Radio Luxem- 302 Radio Vitus 408 Reval 766 Liabach . .bourg 303 Koenigsberg 411 Berne 775 Kiev . .

230 Ste. Etienne . 306.1 Belfast . 2BE Notodden 05.5 Leningrad .

Schaerbeek 309.2 Zagreb . 416 Grenoble 1,000 Leningrad .

236.2 Stettin . . 310 Oviedo 416.7 Goteborg Basle . .

238.1 Bordeaux . 310.2 Marseilles 420 Rabat 1,069 Hilversum . HDO240 Nimes 312.5 Newcastle . 5NO 422 Kattowitz . 1,08o Strasbourg .

246 Juan-les-Pins . 319.1 Dublin . . 2RN 428.6 Frankfort 1,II/ Warsaw . .

241.9 Nurnberg 322.6 Breslau . . 434.8 Freidriksstad . 1,180 StembolMuenster . 326.1 Bournemouth 6BM Seville . . 1,153 Kalundborg .

252.1 Bradford . 2LS 323.9 Almeria . . 435 Wilno . . 1,18o Stamboul .

Cassel . . 329 Gleiwitz . . 441 Brunn . . 1,190 Boden . .

Montpellier . 333.3 Naples . . 448 Rjuiken . 1,250 Konigswuster-256 Kiel . . Reikjavik. 448.4 Rome hausen-Zeesen LP259 Toulouse. . 335 San Sebastian. EAJ8 450 Moscow , 1,380 Motala . .

260.9 Malmo . . Cartagena . 453.8 Stockholm 1,450 Moscow . . RDW264 Lille (Poste du 337 Copenhagen . 458 Paris Ecole Sup. 1,525 Lahti

Nord) 340.9 Paris . . Petit 46o Belgrade . 1,604 Daventry. 5XX267 Strasbourg . Parisien 461.5 Oslo 1,700 Kharkov .272.7 Sheffield . . 6FL Huizen 462 Barcelona . 1,750 Paris

Bremen . . 344 Posen 470 Langenberg . ,Soo AngoraDanzig . 344.8 Barcelona EAji 477.7 Lyons . . BucharestKlagenfurt 348.9 Prague . 484.6 Berlin Norddeich

273 Limoges 353 Cardiff 5WA 491.8 Daventry Ex- 1,850 Carthage275 Ghent . 357.1 Graz . perimental 5GB Huizen .

275.2 Dresden . 361.4 London . 2L0 500 Aberdeen . 2BD 1,870 Kosice .Nottingham 5NG 365.8 Leipzig . 504 Porsgrund . Huizen

277.8 Leeds 2LS 370 Paris . Radio LL 508.5 Brussels . 1,950 Scheveningen.278.8 Bordeaux 370.4 Bergen 517.2 Vienna . . 2,000 Kovno (Kaunas.28o Renne . 375 Helsingfors 535.7 Munich . . 2,650 Paris . . FL283 Colognes. Madrid . EA J 545.6 Sundsvall . 2,800 Temesvar

54


et HEGLEE-SINGER

THREE

A Pure-

tone Gramo-Radio Receiver

MANY three -valve designshave been published in

the pages of the WIRELESS MAGAZINE duringthe past year to meet the diverse needs ofmany thousands of readers. The set described in thisarticle is a special gramo-radio outfit-that is, it isintended first and foremost to give reproduction ofsuperlative quality.

Perfect QualityThe idea behind the

name of the set is per-fect harmony-gleesinging is really a com-bination of soloists,usually unaccompanied,and each voice must beof the best. In the caseof the Glee -singer Threeonly the very best com-ponents have been usedand the result is absolutepurity of reproduction.

No great range isclaimed for the receiver,

View of sub -baseboard wiring of the Glee -singer Three

but it should bring in, under all normal conditions, four orfive transmissions on the loud -speaker with perfection,and it is really good for reproducing gramophone recordsby means of a pick-up.

As will be seen fromthe circuit diagram, thedetector works on theanode -bend principleand is followed by twostages of resistance -coupled low -frequencyamplification.

Reaction ControlCapacity -controlled

reaction is employed andan output choke is pro-vided in the anode cir-cuit of the last valve toprevent the steadydirect current fromdamaging the loud-speaker windings.

By means of a jack

Designed,Built & Tested

oy the "W.M." Staffthe pick-up is inserted in thefirst grid circuit in such a way

that the anode -bend potentio-meter can be utilised for making

critical biassing adjustments.The aerial -tuning and reaction condenser are both pro-

vided with a vernier dial so that fine adjustments can bemade, while a sensitivemilliammeter gives avisible check of thequality of the repro-duction, as will beexplained in detail later

Best ComponentsParticular attention

is drawn to the fact thatonly components of thehighest quality are used,and the cost of con-struction is, therefor e,above the average for athree-valver.

But for efficientgramophone work an

absolutely pure quality of reproduction is essential andthere are many WIRELESS MAGAZINE readers who willnot mind the extra cost when they are assured that

they are getting some-

.0 00

NMI/ 0005/ 000.3

pc,

.006

r R.C. ro:,;UNITS ----mEcb

- 0-50MILLIAMMA

2MFO.

EMF0.

HT+thing above the average.

For example, the mil-liammeter incorporated-a Ferranti-is of theD'Arsonval moving -coil type with sapphirebearings and is pro-vided with a fuse which

L.S. protects the windingfrom destruction in theevent of an excessiveoverload. A spare fuseis provided with eachinstrument.

0OhT-

JACK GB -1 GB -Z GB+

Circuit of the Glee -singer Three, which comprises a detector andtwo resistance -coupled low -frequency stages

LT+

Special WiringIt will be observed

that in the constructiona combination of sur-face and sub -baseboard

55

LT-


The Glee -singer Three (Continued)

Making final adjust-ments to the Glee -singer Three, which is agramo-radio receiver.The loud -speaker in useis a Ferranti exponen-

tial horn

wiring has been adaptedand special attentionshould be given to themethod of mounting theterminal strip. This isactually placed flat alongthe edge of the baseboardand recesses are cut outin the latter to accom-modate the terminalshanks.

On the front panel aremounted the aerial andreaction condensers, themilliammeter, the anode -bend potentiometer, themaster rheostat which servesas an on -off switch, and thepick-up jack.

A glance at the photographs will revealthe layout adopted on the baseboard.Along the edge of the baseboard, lookingfrom the back and reading from left toright, are the output filter choke, power -valve holder, first low -frequency valveholder, the high -frequency choke, thedetector -valve holder and the holders forthe reaction and aerial coils respectively.

Nearer the panel, also from left to right, are the two z-microfarad fixed condensers, the two resist-ance -coupling units, and the 4 %-volt tappcdbattery for applying bias to the grid of the detectorvalve in conjunction with the anode -bend potentio-meter.

Positions of Sub -baseboard WiresUnderneath the panel is mounted the small

.000t-microfarad fixed condenser in the aerialcircuit. It may here be mentioned that the positionsof the sub -baseboard wires do not matter in theleast; they are simply led from point to point andconnected together in the most convenient way.

Constructors will have no difficulty in building theGlee -singer Three. All the essential details are repro-duced in these pages, but considerable time and troublecan be saved by using a full-size blueprint, which acts as a

A SIX -VALVEGRAMO-RADIOSET-THE CON-NOISSEUR'S SIX-IS DESCRIBEDIN DETAIL ON

PAGE 20

56

panel -drilling template, layout guide and wiringdiagram.

Until the end of August copies of the blue-print, which is No. W.M.92, can be obtained forhalf-price, that is 6d. post free, if the coupon tobe found on page iii of the cover is used. Addressyour inquiry to Blueprint Dept., WIRELESSMAGAZINE, 58/61 Fetter Lane, E.C.4.

Keep to Original SpecificationWhen building the Glee -singer Three keep

as closely as possible to the original specificationand layout. If it is impossible to use the same

parts as employed in the originalWIRELESS MAGAZINE design utiliseonly those alternatives that arerecommended.

As soon as all the parts have beenfixed into position, wiring -up can bestarted. This will present nodifficulty if reference is made to the

blueprint or the wiringdiagram reproduced inthese pages. On each,every terminal point ismarked with a letter ofthe alphabet ; theseletters indicate whichpoints should be con-nected together and int

what alphabetical sequence.

How to Wire -up the SetThus, all those points marked a are first

connected in the most convenient way;then all those points marked b, and so onthroughout the alphabet. It does notmatter, as has already been mentioned,how the sub -baseboard wires are arranged.

As regards coils, normally a No. 6owill cover the lower broadcast band (in the

The Glee -singer

.`a a Three

Valves and coils all readyin position in the Glee.

singer Three


A Fine Gramo-radio Setaerial circuit), while a No. 5o should be suitable forreaction. A No. 200 and a No. 15o in the same positionsshould be adequate for reception on the higher broadcastband.

The choice of valves is not difficult if the operatorremembers that the impedance of a valve that has aresistance coupling in its anode circuit should beapproximately one-third of that resistance.

Best Detector ValveThus if the anode resistance is 250,000 ohms

(.25 megohm) as specified, then a valve with an imped-Below, the disposi.ance of the order of 6o,000 to 8o, 000 ohms will be suitable tion of the components ofthe Glee -singer Three is shownas detector.

In cases where the setis used some distancefrom the local stationand the strength is notoverpowering, a similar valvecan be used for the first low -frequency stage : but the gridswing of such a valve is toolimited to handle a great dealof energy and in the case ofsignals that are initially verystrong a valve with a muchlower impedance and greatergrid swing is advisable. Thevalue in this case can be any-thing between 20,000 and40,000 ohms.

Last -stage ValveOf course, the last valve

should be of the super -powertype with an impedance ofless than 5,000 ohms. Something about 3,500 ohms willbe suitable for most coneand even moving -coil loud-speakers.

To carryout a roughtest of theGlee -singerThree insertthe valves

Another view of the Glee -singer Three. Note the

output choke on the left

16r4 8"

ADRILL COMOEMER 4 I CO OUT TO :WITMOONTIUG MOLL* 2%"I MILLiAMMETER.TO TEMPLATE USEDSUPPLIED BY

MAKER

\ I

4 . .1 7f

i , 64-- 3 te.-IIPOS ITIO OF 3k:

136.5LBOARO ii .F4 -R'" :

Panel layout of the Glee -singer Three

and coils and apply thefollowing voltages : Tap

off 3 volts negative on thebiassing battery for the detec-tor valve (mounted on thebaseboard). To H.T. -I- apply120 to 150 volts, while toG.B. -I apply from 3 to 6volts and to G.B. -2 anythingfrom 6 to 18 volts, dependingupon the type of valve.

Now turn the master rheo-stat full on and adjust bothreaction condenser (right) andanode -bend potentiometer(left) until the slight rustlingor hissing sound is heard fromthe loud -speaker which indi-cates that the set is on theverge of oscillation.

Greatest VolumeTurn the knob of the aerial -

tuning condenser (left) untila transmission is picked up,when the potentiometer (andassociated battery) and re-action condenser should be

adjusted for the greatest volume.It is at this stage that the milliammeter begins to

play a most useful part. If the reading is not quitesteady, distortion is taking place and this should becured by readjusting the bias applied to the grids ofall three valves. The needle will flicker even whendistortion is not bad enough to be appreciated by theear, but nevertheless it is there and should beremedied. Adding more (or applying less in the caseof the detector) negative bias will usually produce thedesired result-an absolutely steady reading.

Conserving the High Tension SupplyActually the milliammeter only indicates the

amount of current passing in the anode circuit of the lastvalve. By increasing the amount of grid bias, the high-tension consumption will be reduced and in this waythe supply can be conserved. T+ is a safe rule to apply

57


The Glee -singer Three (Continued)

4.;-0003 RLACT1011 COP01115ER

RORK RATER fILL0-5IAPIR0CTUk

0.1.11[PRirtrNM sa

-0005 00845. 1)10%COR)R.MLR

0[ I@ 1 0) )MOARG RUM

-fvegnIm

R.0 COURL1KUmr

'Ofi yourTAPPER8410045

PAta 19 -X8 -If a really good super -power valve is used in the

last stage and the first low -frequency valve is

Fik"..150ARD 16 58

® t Cc: -)Z c)1Q4,

MS.

This layout and wiring diagram of the Glee -singer Three can be obtainedas a full-size blueprint for half-price, that is 6d. post free, up till August31, if the coupon on page iii of the cover is used. Ask for No. W.M.92

,is much grid bias as the valves willstand.

Alteration of the detector biasmay be needed when using the set asa gramo-radio amplifier. Connect themagnetic pick-up (special connectionsare required for electro-static pick-ups)to the plug and insert it in the jack.

Pure ReproductionIn this case, the milliammeter is

particularly useful, for one is sure ofgetting absolutely pure reproduction(provided the correct valves areused). For gramo-radio work with asensitive pick-up it will be almost -essential to use a valve with animpedance of 20,000 to 30,000 ohmsin the first low -frequency stage, as

any valve with a higher impedance is likely to beoverloaded.

An ordinary horn -type loud -speaker is notrecommended for use with this receiver, unless itbe one of the exponential or logarithmic type, as thebass will not be well reproduced. The best resultswill he obtained from a modern exponential horn,cone, or moving -coil loud -speaker.

Excellent Quality Assured with This Set

110111111VALVES TO USE IN

THE GLEE -SINGER THREEVolt-age Detector 1st L.F. znd L.F.

2 -volt

Cossor 2 zoRCMullard

PM1ASix -Sixty

2 toRC

Cossor 21oHFMullard

PM1LFSix -Sixty

210LIF

Cossor 22oPMullard

PA 4252Six -Sixty

2I5P

4 -volt

Cossor 4IORCMullard

PM3ASix -Sixty

4075RC

Cossor 410HFMullard

PM3ASix -Sixty

4075HF

Cossor 410PMullard

PM254Six -Sixty

425SP

6 -volt

Cossor 6 toRCMullard

PM5BSix -Sixty

6o75RC

Cossor 61oHFMullard

PM5XSix -Sixty

6o75HF

Cossor 6o i PMullard

PM256Six -Sixty

625SPu IMEISSMSE MMMMMM SE MMMM MMMMMM OEMS

chosen according to particular needs, the Glee -singer Three will be found to give unimpeachablequality.

We have invited Mr. J. Godchaux Abrahams totry out this receiver independently and his testsshow that although the Glee- singer Three doesnot possess great range, the quality of the fewstations that can be picked up on the loud -speakeris superb. No doubt many readers will be able toget greater range than we normally claim for thisreceiver with an average aerial and earth system.

ESIEE11100

COMPONENTS REQUIRED FOR5-Ebonite panel, i6 in. by 8 in.

(Radion or Becol).I-.0005-microfarad variable con-

denser (Cyldon or Burndept).I-.0003-microfarad variable con-

denser (Cyldon or Burndept).2-Vernier dials (Harlie or Formo).x-Milliammeter, reading o --3o (Fer-

ranti type RIP).5 -7 -ohm panel rheostat (Lissen,

Peerless, or Igranic).5--400-ohm panel potentiometer

(Lissen, Ormond, or Igranic).5-Plug and jack (Igranic typa P63).2-Resistance-coupling units (Dubi-

lier, R.I. & Varley or Mullard).5-.006-microfarad fixed condenser

(Dubilier, T.C.C., or Lissen).2-2-microfarad fixed condensers

(Dubilier, T.C.C., or Hydra).

THE GLEE -SINGER THREE3-Anti-microphonic valve holders

(Benjamin, Lotus, or W.B.).2-Single-coil holders (Lotus, Lissen,

or Magnum).I-High-frequency choke (R.I. and

Varley, Cosmos, or Igranic).I-Output filter choke (R.I. and

Varley, Igranic, or Ferranti).I -41/2 -volt tapped grid -bias battery

(Siemens or Ever -Ready).5-.cool-microfarad fixed condenser

(Igranic, Dubilier, or T.C.C.).1-Terminal strip, i6 in. by I in.

(Radion or Becol).5-Terminals, marked: Aerial, Earth,

L.T.+, L.T. G.B.+,G.B.-5, G.B. - 2, H.T. ,

H.T. - , L.S.+, (Eelex).6 -2 -ft. lengths insulated wire

(Glazite).1-Cabinet with 8 in. baseboard

(Edwards).

58


Steps the B.B.C. Is Taking for

Doubling the Nilier of licence Holders!SOMEWHERE it

was suggestedrecently that inofficial circles theview was held thatbroadcastinglicences hadreached saturationpoint. This is en-tirely fallacious.While there is stillan enormous num-ber of pirates, usersof hidden apparatuswho possibly couldonly be unearthedby a long, tiresomeand expensive houseto house search,there remains also,incredible as it maysound, a percentageof the populationwhich has not evenyet heard of theB.B.C., or what it is here

Talk of " saturation point"therefore be dismissed until suchtime at least as the licence recordsshow a figure of four millions.

Specially Contributed to the " Wireless Magazineby Savoy Hill Officials

FEE

10I -WIRELESS TELEGRAPHY

1..e 192g .1 iv2.5

R Aft...gl....a.asetit 5 ...P.LI libd.tAtiolvg LT.1),--rri ill`rgr8:1 0" '

,INsoin Iiiioglii,oi if Arose is pick lettere/ aryll

f T......a..1.(2/ " 'f,,M4 1V t.Ne i'llseii Cs' i , is hereby

authorised tnf0,,ct in all respects to the condition.. set forth on thd hack hereof) to

t taidieh ti lin elosi;et.stion for the porno.," of FIDC.IVillg rile.6.ageS at s.caleit.(1.7.iist. ..,

as--4wirOFtiorfe12.9. for 'e period ending on the ditto taToi:n6'sho"":e'.

The payment of the the of too shillings is hereby acknowledged

Issued on to halt ofthe Foot lisisteritienerei

If n .issireil los mome!mob 1.03e.11043I.

wireless Ts.hr the wireless Tsisthltismor wireliso mow

CTS, 1904-1925.

If you own a wireless set and are not familiar with the above licence formyou must be a " pirate" ! The cost of a licence for any set is 101- a year-

surely a small enough outlay for the entertainment that is available !

for.can

What the B.B.C. Is Out to DoThe B.B.C. is definitely out to

double the present licence figures.Additions to its salaried personnel,plans for the improvement of itstransmissions and the introductionof alternative programmes, the forma-tion of new organisations which shallhave their part in the vast nationalenterprise which functions throughSavoy Hill, the contemplated erectionof a great new edifice in the heart ofLondon as a home of broadcastingwhich, like the British service itself,shall be a pattern and example tothe world-all these schemes pointto the intention of developing thebusiness side as well as the artisticside of the broadcasting machine.

What is being done towards theaccomplishment of these aims? TheB.B.C. has already made a specialstudy of conditions in the Northand has introduced the regional ideato Northerners by means of what

might be termed communal pro-grammes. Manchester has, in fact,become already the centre for thedistribution of programmes through-out the Northern area and the artistescontributing to its S.B. items aredrawn from the studios of Liverpool,Leeds, Bradford, and Sheffield asrequired.

To enhance the musical side of theNorthern programmes a new per-manent orchestra has been formed inCottonopolis, consisting of twenty-seven members, many of whom aremembers of the Halle Orchestra,and quite a number of whom are well-known, not only as orchestral per-formers, but also as solo artistes.

Members of the OrchestraMr. T. H. Morrison continues as

conductor, while Mr. John Bridge isthe leading violinist and deputy con-ductor. The principals are DonHyden, deputy -leader; LeonardHirsch, principal second violin ; FrankPark, principal viola; Clyde Twelve -trees, principal 'cello; Alfred Stott,principal double bass ; Joseph Lingard,principal flute; Alec Whittaker, prin-cipal oboe; Pat Ryan, principal

59

clarinet; ArchieCamden, principalbassoon; OttoPaersch, first horn;Charles Birtles, firsttrumpet; Sam Holt,first trombone;}Tarry Hoyland,bass trombone, andJohn Massey,timpanist.

The formation ofthis permanent.orchestra has madeit possible for Man-chester to put onmany more orches-tral concerts in theafternoon thanhitherto, apartaltogether fromevening concerts.

While moves werebeing made in theNorth with the root

object of encouraging a greater useof the broadcasting medium, theB.B.C. was busy also in the West,where it started an experimentalscheme, in conjunction with the WelshNational Council of Music, theNational Museum of Wales and theCardiff City Corporation, for a" National Orchestra of Wales," toperform in public and to broadcastnationally.

Six Weeks' ExperimentA six weeks' experiment was so

successful that, despite the fact thatno further use of the orchestra forbroadcasting purposes was projected,pending the opening of a secondseason of twelve weeks, on October4 next, weekly concerts will becontinued at the request of listeners ;and when it is remembered thatthroughout the world orchestras havehad to be heavily subsidised bynational and civic authorities, thework which is being done in Waleswithout any charge on the ratepayersassumes a deep significance.

A third and equally importantdevelopment in progress is the re-organisation of the National Chorus.

I 'Wireless Magazine. August, 1928

Doubling the Number of Licence Holders ! (Continued)

In the past, this chorus was formedas and when required by partiesdrawn from various amateur choralsocieties which operate in centralLondon (for example : Lloyds, theCivil Service, the Railway ClearingHouse, etc.), together with the pro-fessional Wireless Chorus.

For Big Choral WorksThe B.B.C. considered that past

experiments justified the use of a largechorus for important works on a bigscale, as distinct from the professionalWireless Choruswhich is used regu-larly for studio per-formances. Accord-

' ingly, plans were laidfor a large permanentchorus in addition,which will rehearseregularly once eachweek during thewinter months andwill retain its per-sonnel practicallyunchanged from yearto year. This choruswill perform thebigger choral worksat certain of thepublic symphonyconcerts which areorganised from timeto time by theB. B. C .

Choral singing bylarge bodies ofchoristers is an artin which the com-petent amateur ispre-eminent. Forthat reason, the newNational Chorus willconsist entirely ofamateurs. It will beabout 250 strong andeach member will be carefully chosen.The chorus will, of course, be ade-quately balanced.

I

unless he or she is, and agrees toremain, an active member of someother amateur choral society.

The chorus will be trained by Mr.Stanford Robinson, the B.B.C.Chorus -Master, and will performunder various conductors of inter-national repute next autumn andwinter. It will appear in publi,' aboutthree times each season.

The scheme is only in its infancy;but the B.B.C. hopes that it may bepossible to produce a chorus of super-lative merit, leading to a revival of

or " still " pictures it is yet too earlyto say; but progress is undoubtedlybeing made with the various inven-tions with which experiments arebeing carried out. The B.B.C.engineers were, for instance, muchimpressed recently by a demon-stration conducted by Captain OttoFulton, an inventor, at the ResearchDepartment of the Corporation atClapham.

Transmitting PhotographsPhotographs were transmitted on

2LO's wavelength

Receiving Licence Conditionsr. The Licensee shall not allow the station to be used for any purpose other than that

of receiving messages in the premises occupied by the Licensee.

a. The station shall not be used in such a manner as to cause interference withthe working of other stations. In particular, reaction must not be used to such an extentas to energise any neighbouring aerial. (See Note).

3. The combined height and length of the external aerial (where one is employed)shall not exceed zoo feet. An aerial which crosses above or is liable to fall upon or tobe blown on to any overhead power wire (including electric lighting and tramway wires)must be guarded tp the reasonable satisfaction of the owner of the power wire concerned.

4. The Licensee shall not divulge or allow to be divulged to any person (other thana duly authorised officer of His Majesty's Government or a competent legal tribunal)or make any use whatsoever of any message received by means of the station other thantime signals, music 1 performances, and messages sent for general reception and messagesreceived from a licensed experimental station in connection with experiments carried outby the licensee.

5. The station and this licence shall be open to inspection at all reasonable times byduly authorised officers of the Post Office, who will produce their cards of identity onrequest.

6. This Licence may be cancelled by the Postmaster -General at any time either byspecific notice in writing, sent by post to the Licensee at the address shown hereon, orby means of the general notice in the London Gazette addressed to all holders of wirelessreceiving Licences, and will be cancelled on breach of any of the foregoing conditions.In the event of cancellation no part of the fee will be returned.

7. The Licence is not transferable.

Interference is" note " or " whof interference is" whistle " is auis due to some e x

NOTEtaking place if a continuous " note " or " whistle " is heard. If this

istle " changes when the wavelength of the receiver is altered the causein the receiver and reaction must be reduced until no " note " or

dible. If the " note " or " whistle " does not change the interferenceternal source.

Any permaneHead Postmastnumber and dat

LiLifa temporary

Do you remem" Wireless Ma

No Need for FearThere need be no fear on the part

of existing amateur societies thatthis new move of the B.B.C. willinterfere with, or hinder, their ownwork. It should rather help forwardthe appreciation of choral music, themost democratic of the arts. Hencethe B.B.C. insists that no one shallbe a member of the National Chorus

nt change of address must be promptly communicated to theer of the district In which the station is situated. The seriale of expiration of the licence should be quoted in all cases. Notice

change is not required.

ber the conditions under which your licence is issued? Everygazine" reader, of course, makes it a point of honour to

observe Clause 2 : see that others do, too !

choral singing, which has sadlydeclined since the war. Listenershave already been enabled to recap-ture the pleasures of unison songsthrough the revival of communitysinging; the B.B.C. is now aiming tohelp them to test the happiness whichis to be found in vocal harmony.

The next development fore -shadowed is in the introduction ofa scheme for transmitting illustra-tions in connection with the broad-casting service. Whether this newfacility will take the form of " live "

60

between the OxfordStreet station andClapham and theresults were good.The system is nottelevision, but tele-photography, andcould probably beused for the broad-casting of weathercharts, illustrationsto talks and stories,facsimile writing,finger -prints and anyother purpose wherepictorial representa-tion might be ofservice in elaboratingthe spoken word.

So far, transmis-sion has successfullybeen achieved overa distance of 65omiles and the timeof each single pic-torial broadcast isabout three minutesand a half. VariousEuropean capitalshave adopted thedevice and it is un-derstood that theregular insertion of

pictorial broadcasting in certainforeign programmes will begin nextautumn.

Close Watch on DevelopmentsThe B.B.C. engineers are closely

watching developments in this direc-tion and British listeners will benefitimmediately the advantages of adopt-ing any invention are found to be inthe interests of the broadcastingservice.

EArticles by B.B.C. Officials appearIL in the " W.M. " every month

IWireless Magazine. August, 1928

THEVALUE Of FOUR-VOLTVALVESUNTIL a few weeks ago

the four-volter hadbeen so neglected that itshowed signs of becomingthe Cinderella of the valvefamily; recent events, however,show that it has dormant goodqualities which are at last seeing thelight of day.

Abolishing Four -volt Valves?In some quarters the drastic step

of abolishing four -volt valves alto-gether was advocated with somepersistence, but a careful considera-tion of the position shows that itwould be better to retain four -voltvalves only, and scrap two-voltersand six-volters, than to pursue anyother course.

We are quite aware of the valueof the two -volt valve as regardsutility in practical working and,moreover, we are also aware of thesuperiority of the six-volter, char-acteristic for characteristic, whenfilament wattage is taken intoaccount. But there is every reasonfor asking the question : " Whatadvantages can the six -volt valvegive us that the four -volt valvecannot offer on its own ? "

Now it will be readily admittedthat the chief argument in favourof the use of two -volt valves is thatonly a two -volt accumulator isrequired. But what advantage doesthis give us in practice?

Better Four-voltersTake two equivalent power valves

of the two- and four -volt classes andnote their filament consumption. Inmost cases the consumption of thefour -volt valve will be half thatrequired by the two-volter and,moreover, the characteristic of thefour -volt valve will be very muchbetter. This is true of valves of almostany make, eves in spite of the factthat four-volters have not beendeveloped to anything like the extentthat two-volters have during the pastyear.

Where, then, is the advantage ofthe two -volt accumulator? For this,as will be readily seen, must be twicethe size of a corresponding four -voltbattery in order to give the same

By D. SISSON RELPH

number of working hours. It willthus be evident that the four-volterhas the advantage'over the two-volterof reduced filament consumption andgreater efficiency.

Now what can we learn from com-paring the four-volter with the six-volter ? Well, in the first place thesix-volter shows no economy offilament current, characteristic forcharacteristic, over the four-volterand the efficiency of the six-volter isvery little, if any, greater than that ofthe four-volter. In this case, althoughwe save nothing in consumption byusing a four -volt valve, yet we dosave one cell of an accumulator-which is again an advantage infavour of four-volters over six-volters.

Question of Filament EfficiencyI have discussed this matter at

length with several people interested'in the manufacture of valves andfind they agree that in most cases avalve with a four -volt filament can bemade to do everything that a valvewith a six -volt filament is capable of,but it is not possible to make a valvewith a two -volt filament equivalentto a valve with a four -volt filament,except by increasing the filamentconsumption.

The Position of PortablesSome readers will immediately ask

what will happen in regard to port-able sets if four -volt valves take theplace of two -volt valves. Well, theanswer is that although two cellswould be needed, each of these couldbe approximately half the capacity-and, therefore, approximately halfthe size and weight-of the corre-sponding two -volt cell that wouldbe necessary with two-volters,because of the lower total of

61

filament consumption.Already portable -set

manufacturers are makinga move in this direction,as also are makers of ordin-

ary receivers.I am not, by any means, sug-

gesting that two- or six -volt valvesshould be abolished in favour of four-volters, but I would suggest to readersof the WIRELESS MAGAZINE that thereare advantages to be obtained byusing four -volt valves which, per-haps, they have so far overlooked.This autumn is likely to see a numberof interesting developments in thefour -volt class.

When We Can StandardiseThere is one last point. One might

suppose that in the course of timemanufacturers will be able to makevalves with two -volt filaments asgood as those with four -volt filaments,with the same consumption, but theopinion of at least one group ofmanufacturers is that for many yearsto come four -volt valves will alwaysbe more efficient than two-volters forthe same consumption.

Any revolutionary development,however, in the process of makinglow temperature emission filamentsmight, at any time, make it possiblefor manufacturers to standardise ontwo-volters only. Until that timecomes, though, it seems that it will bebest to concentrate on the perfectionof the four -volt valve.

Continental Notes(Continued from page 54)

from his South American tour and Iwas present-through my earphones-at the welcome accorded by theUnited States to Captain Koehl,Baron von Huenefeld and MajorFitzmaurice, after their rescue onGreen Island and their subsequentarrival at New York.

Again, more recently, when CaptainWilkins and Lieutenant Eyelsonlanded on the Tempelhof Aerodromeat Berlin, the German stations broad-cast their reception. The return ofthe crew of the aeroplane Bremenand the arrival of the s.s. Columbus,were each relayed from Berlin.


%fijordtaigeeigatti

Near Milnthorpe

FOLLOWING the tours made atEaster time with the Sunshine

Five, I spent a few days recently intouring round the north-west ofEngland with a view to ascertainingwhat results could be obtained in thesedistricts. There is a large numberof very enthusiastic listeners in thisarea, so that the results are of particu-lar importance.

Route of My TourThe route of the tour was through

the Potteries to Liverpool and thenceon to the Lake District. This route,incidentally, took me right pastDaventry, which was to be the princi-pal source of entertainment in thoseparts of the country more remote fromcivilisation. Those readers who knowthe countryside around Daventrywill appreciate the very fine settingwhich the masts make against thesunset, which was the inspiringpicture I took with me on my roadnorth.

I got as far as Stone, in Stafford-shire, the first night, and here theset was brought into commission forthe first time. It gave excellentresults. On the long waves I obtainedDaventry, Radio -Paris, and Berlin(Zeesen) at very good strength, whileHilversum and Ryvang were alsoaudible, although somewhat fainter.

On the short-wave band, 5GB andLangenberg were tuned -in withoutany difficulty. My geography being alittle feeble, it was not until the nextmorning that I discovered myproximity to Stoke-on-Trent and I

By J. H. REYNER, B.Sc., A.M.I.E.E.Constructional details of this receiver weregiven in the May issue of "W.M."

obtained without any difficulty.These are daylight ranges and, as

the time waslimited, tests

on distant

did not,therefore,listen forthis stationwhich would betuned in rather to-wards the bottom ofthe scale and, consequently,below the general run of stations. Ihave no doubt, however, that thisstation could have been receivedwithout difficulty, judging by theperformance of the set.

KEtLI:KTriotm5Ecx

tiby 'were- ki

5EATOLLER

AP1BLE.510Ed

7 Moder/nem

Route of J. H.Reyner'sNorth -country

Tour

The next time the set was broughtinto commission was in Liverpoolitself. Here again, excellent resultswere obtainable. Both Daventry'scame in at good strength, whileManchester and Liverpool were

62

At Ullswater

stations were not then conducted.The route went on through Lan-

caster and Kendal to the Lakes, theultimate goal being a small farmhouseat a place called Seatoller, where Ihad recollections of a previous happyholiday.

This village is at the extreme endof the Borrowdale Valley, the mostpicturesque of all Lakeland scenery,and here we encountered the firstset -back. It was only with consider-able difficulty that I was able to tunein Daventry at all, and no otherstation was audible with the excep-tion, rather to my surprise, of Radio -Paris, which in its lucid momentswas quite comfortably intelligible.Daventry undoubtedly was a disap-pointment and was also subject tofading, the strength at the bottomof a fade being such as to render himvery difficult to follow.

Poor Spot for RectptionI cheered up somewhat on the

following day, when I made inquiriesfrom others in the village and foundthat it was a very poor spot for recep-tion. I had, indeed, had suspicionsof this, for the village is hemmed inon nearly every side by the moun-tains rising in height to 1,50o, 2,000

and in some cases, 3,000 feet, so thatone might expect a certain amountof shielding.

I learned that, although on an out-side aerial, a three -valve receiverwould receive Daventry on the loud-speaker, yet in order to obtain goodreception and in order to get distantstations, particularly on the zoo to500 metre band, a five -valve set wasrequired. Nothing less was, appar-ently, of any use.

That the poor reception was dueto local conditions I was able toconfirm later on in other parts of thedistrict. Some photographs weretaken at this spot, one showing thefarmhouse where we stayed, withmyself explaining the mysteries ofwireless to the daughter of the house.The photographs reproduced givesome indication of the mountainousnature of the country surrounding.

A short trip down the valleytowards Keswick was made the nextday and the upper route was taken,this winding several hundred feetabove the bottom level. The differ-ence in reception was very markedand another photograph shows theset in operation at a particularlybeautiful spot overlookingDerwentwater.

The camera was 15yards away from theset when this photo-graph was taken andevery word was dis-tinctly audible at thisand even greater dis-tances when the set wastuned to Daventry.No short-wave stationswere obtained in day-light, although Man-chester could be heardfaintly.

A tour round the re-mainder of the districtwas then made, theroute being Keswick,Troutbeck, Patterdale,Kirkstone Pass, Amble -side, Keswick. Tests weremade at various points,one such test taken on theroad just overlooking Ullswaterbeing shown in the second photo-graph. Throughout the district thesame variability in reception wasnoted.

At some places quite good resultscould be obtained, while in othersthe response was disappointing.Daventry was the best station in allcases. The air -line distance from


Daventry to Seatoller is x 8o miles.On the return journey, therefore,

a test was made as soon as we wereclear of the Lake District itself. Itso happened that there was no actualtransmission until we reachedMilnthorpe, which is some sixteenmiles north of Lancaster. Herea test was made in a very picturesquespot, as indicated by a photograph,and Daventry was received at excel-lent strength without any difficultywhatever.

Daventry at 150 MilesThe airline distance here is 15o

miles, and the strength indicatesthat the set is good for the consider-ably greater distance when troublesdue to excessive shielding are notintroduced.

On the whole, therefore, the secondtest may be considered satisfactory,although it was not as good as I hadhoped. As far as convenience wentthe receiver behaved excellently. Itwas always ready for use withoutany attention even after the severebumping that it occasionally receivedin going over some of the roads.

One point I have discovered inactual operation which may puzzle

(Above)-Testing theSunshine Fiveat Seatoller, avillage sur-rounded byhills. (Right)-By the sideof Derwent-

water

63

THE ATTENTION OF PROS-

PECTIVE CONSTRUCTORS

OF THE SUNSHINE FIVE

(WHICH WAS FULLY DE-

SCRIBED IN THE MAY

ISSUE) IS CALLED TO A

SPECIAL ARTICLE ON

PAGE 77

one or two readers and that is that anasty threshold howl is sometimesliable to be set up just before goinginto oscillation. This howl may pre-vent the reception of stations alto-gether, for one is apt to mistake it forthe actual oscillation itself and, there-fore, the carrier wave of the stationrequired is not heard.

Actually this threshold howl occursa little before the oscillation pointand if one continues through it, thetrue oscillation will be found and thestation can be pulled out of the carrierin the ordinary way.

I mention this method of achievingresults despite the howl only in caseit proves obstinate, but in -a generalcase it can be obviated completelyby a readjustment of the voltage onthe detector. This is supplied witha separate tapping and it should bekept at a fairly low value. Actually,I used about 36 to 42 volts and if thevalue is increased much above thisdifficulties may arise due to this cause.


DavidWise,

Violinist

THERE has beenundoubtedly an

attempt this monthto lighten the pro-grammes, and thoughover -much synco-pated music stillprevails, there isobviously a publicfor that type of thing.Many well-knownvariety and musicalrevue stars have figured prominently.

Some Popular ArtistesLauncelot Quinn, made popular by

his success in Hit the Deck and knownto northein audiences long before hereached London, was heartily wel-comed therefore when hereturned to Manchester andbroadcast some of his successesfrom that station.

Thornley Dodge, anothername of the old Gaiety times,also figured in the same pro-gramme with Colleen Cliffordand Walter Bayley. The lastis a clever bird mimic.

Many favourite broadcastershave been heard, including

3roadcast LIS1C

of the Month

SydneyColtham

ElsieSuddaby

Reviewed by Studiusthe two clever partners,Jeane Paule and LeonieLascelles, both from Londonand the provincial studios.In every case their songs are

different, witty, andwell played.

De Groot, with hisorchestra ; HelenaMillais, with her in-imitable and reallynatural " fragmentsof life " with our " OurLizzie " to portray

GwladysNaish, " The

WelshNightingale "

Fred Elizaldeand his bandat the Savoy

them; Helen Gilliland,recently appearing inLady Mary andknown to listeners aswell for her formerbroadcast inThe Cousinfrom Nowhere; JackBuchanan, the popularmusical comedy star;and Gene Gerrard,who appeared inKatja the Dancer andThe Desert Song, are

all artistes who have striven to makea brighter London; while most popu-lar of all are the Chariot Hours.

A special programme is being ar-ranged by Mr. Charlot for July 26,as this date marks his birthday, andmost of the original company will beheard.

Last, though by no means least,comes a return of Arthur Prince,the well-known ventriloquist, withhis famous companion " Jim,"

64

Even the plays have been a littlelighter in texture, a good announce-ment being the little work, SomethingIn the Air, written by Harold Simp-son, author of The Nine o'ClockRevue, Dover Street to Dixie, andother revues. Very tuneful musicwas written for this by StanleyHolt, who conducted the RevueChorus and B.B.C. Dance Orchestrafor the occasion.

One would like to see the amountof light orchestral items increasedstill further. The dance bands arc

well supplied by the performances orFred Elizalde and his orchestra at theSavoy, as well as by M. GeorgesBoulanger, who conducts a Tziganeorchestra.

The music heard from the Carltonunder the leadership of M. ReneTapponnier, as well as that fromSignor Colombo at the Hotel Victoria,is on a higher plane. Classical as wellas the more ordinary popular musicis heard, most perfectly played.

Special ProgrammesSpecial programmes are always

popular, though it would be as wellsometimes to give us some of thelesser known works of the composers.A special Spanish programme shouldbe noted, when the best-known worksof De Falla, Granads and Albeniz,were heard, carried out by theorchestra, with De Brosa and Gert-rude Johnson as soloists.


-what Mr.Vincentsays about the"Chummy Four"

June 26th, 1928."On Friday last, June 22nd, between 9.3o p.m.

and 12.30 a.m., I tuned in on the loud-speakerthirty-three stations, including 2 LO and 5GB , and when Isay on the loud -speaker, I mean that the majority ofthe stations could be heard upstairs when the set wasworking downstairs.

The only other set that I have had that was aseasy to operate as this one was a seven -valve super -het, and that easily lost on the score of noisiness andpurity of tone.

Up to the moment I have had nothing to comparewith this set in respect of range, simplicity of tuning,or quality of reproduction, and I congratulate you."

Yours truly,(Signed) FRED VINCENT.

P.S.-This is my first experiencewith a screened grid valve.

USE THESE VALVES IN YOUR "CHUMMY FOUR" AND GET MAXIMUM RESULTS :--

1st Valve 2nd Valve 3rd ValveCossor Screened Grid Cossor 210 R.C. Cossor 210 L.F.

22/6 10/6 10/6 20/6

4th Valve.Cossor 230 P


The Cossor 2 -volt ScreenedGrid Valve plays a bigpart in the success of the

" Chummy Four."

Ensure maximum results from yourReceiver-use Cossor Valves throughout.Cossor Valves are designed to work to-gether-to help one another in buildingup weak signals-to reproduce withperfect clarity of tone and ample volume.Ensure complete success-

use Cossor Valvesthroughout your Set

The Valves that improveany Receiver

Advt. A. C. Cossor, Ltd., Highbury Grove, London, N.5

65

5277


HelenaMillais

Another concert ofinterest was that ar-ranged during thelifetime of the lateSir Herbert Brewer,which he had hopedto conduct himself.Under its title, " OnSevern's Banks," itcomprised works ofmany of the bestknown if not themost musical of Eng-lish musicians, including Sir EdwardElgar, Sir Hubert Parry, Sir HerbertBrewer, Basil Harwood, GustaveHolst, Vaughan Williams, and Her-bert Howells.

Apart from the appearances ofLafitte, the famous pianist, andArnold Trowell, the violoncellist, themonth has not been conspicuous forsolo performances. But that does notmean that no good playing has beenheard; far from it. The B.B.C. have,however, refrained from putting outmoney merely on big names.

E.Casati

David Wise : ViolinistIt would be difficult to find a better

player than David Wise, a youngviolinist who has been heard fromhalls and in the Children's Hour at2LO, as well as at several specialrecitals. His tone is rich and warm,and he has a peculiar facility forbroadcasting.

Amongst the 'cellists a welcomere -appearance was made by a veryearly broadcaster, namely, Miss Bea-trice Eveline. Kathleen Moorhouse,

Broadcast Music ofthe Month (Continued)

of the Halle Orchestra, and CedricSharpe have also been heard togood advantage.

Amongst the singers, many ofthe B.N.O.C. artistes have been

heard, prior to theirstarting their autumnseason in September-Sylvia Nelis, Hed-dle Nash, NormanAllin, and KingsleyLark amongst them.Best of all, per-

haps, was MissGwladys Naish,

DorothyKitchen

queen of coloratura singers, who haswell earned the title of "The WelshNightingale."

Amongst other familiar names, oneremembers the performances of Wini-fred Fisher, Gladys Palmer, ElsieSuddaby, and Dorothy Robson, be-cause they early learnt the art ofbroadcasting; consequently, we donot have to strain to discover whetherthey are singing in English or aforeign tongue-a thing not alwayseasy to discover with some of thenewer artistes.

Sport, already too well represented,had formed the subject of talks by

Georges Boulanger,leader of TziganeOrchestra at the

Savoy

Mr. Peter Freemanand Mr. F. R. Stain -

Clifford ton, also Lieut.-Col.Collinson M. F. McTaggart.

Probably, however,the most popular" talkers " are mem-bers of the RoyalFamily, and the mostpopular undoubtedlyH.R.H. the Prince ofWales.

His address, there-fore, on July i for the annual "Dayof Remembrance" Parade at theGlasgow Cenotaph, and the christen-ing of the new ship, H.M.S. York, bythe Duke and Duchess of York onJuly 17 may be considered as two ofthe most popular broadcasts of themonth.

Too Much Gramophone?The main faults of the programmes

of this month appear to be a super-abundance of gramophone recordsand the predominance of religiousdaily services and music.

Those readers of the WIRELESSMAGAZINE who favour push-pull low -frequency amplification will be gladto know that in the price of Ferrantipush-pull transformers is includedthe royalty payable to the StandardTelephones and Cables Co., Ltd.,who hold a patent on this system ofcoupling. They are therefore fullyand automatically licensed by buyingthese components. Full particularscan be obtained from Ferranti Ltd.,of Hollinwood, Lancashire.

NEXT MONTH'S ISSUE OF THE " WIRELESS MAGAZINE" WILL CON-TAIN FULL DETAILS OF A DE -LUXE FRAME -AERIAL FOUR,VALVER :

ORDER YOUR COPY NOW TO AVOID DISAPPOINTMENT-PRICE 1/,

66

Complete with SlowMotion, Knob & Dial

Yes, you may believe your eyes ! . .

a condenser with slow motion, knoband dial . . . and that condenser aDubilier . . . all complete for 12/,

The Dubilier K.C. Condenser is spe-daily designed to give adequate dis-tribution of the stations round thedial and true kilocycle tuningwhen used with the DubilierToroid. You can get noother type of condenser todo this, least of all at

the price.

1.1 snot tamable from your dealer send directto us mentioning your dealer's name and

address.

it311-ie

Reg. Trade Mark. ©156

Advt. of Dubilier Condenser Co. (i925). Ltd., Ducon Works, Victoria Rd., N Acton. W.3

67


LEWCOS COILSgi

lead again !

(Regd.)

`Q' COILSSpecified in the

"Q Coil Four"in "Wireless Magazine" for May

AERIAL COILS - - 15(Ref. Q.A.) I-

H.F. TRANSFORMER 21/(Ref. Q.S.P.)

As these coils cannot be supplied from stock,place your order at once and ensure earlydelivery. Obtainable from all good radio dealers.

Or write for particulars :The LONDON ELECTRIC WIRE CO. & SMITHS LTD.

Phone: CHURCH ROAD, LEYTON, E.ioWaltItamstmo 2531


A Moving -coilLoud -speaker

PARTICULARLYneat in appear-

ance is the new Zampa moving -coil loud -speaker recently put on themarket. Two models are available,one to work from a 6 -volt accumu-lator or trickle charger connected toA.C. mains and the other for D.C.

mains work-ing. Theformer modelhas a con-sumption of.5 ampere.

In bothcases the

Zampa resistance ofcud -speaker the moving

coil is 1,500 ohms, while the dia-phragm is supported with oiled silk.The over-all dimensions of the com-plete instrument are as follows :Height, 9i in.; width, 81/2 in.; anddepth, 9 in.

These Zampa loud -speakers aremanufactured by the Mic WirelessCo., of White Horse Place, MarketStreet, Wellingborough.

CHINESETELEGRAMS

1

I IN MORSE !OEM

THE transmission and receipt oftelegrams in China is not so easy

as in most other countries, becausethe Chinese language lacks an alpha-bet and expresses itself by charactersand signs that represent words.

In consequence, for purposes oftelegraphing a list has been made ofsigns in quantity sufficient for ordin-ary correspondence, and to each oneof the signs a different number isis given, which is transmitted by theMorse telegraphic system.

Nearly Ten Thousand CiphersThe code consists of 9,800 ciphers,

the whole forming a pamphlet offorty-nine pages, each one of whichcontains ten series of twenty charac-ters with its corresponding number.On receipt of a telegram the operatorlooks up in his book the charactersrepresented by the numbers trans-mitted by the apparatus and trans-cribes them into Chinese. F.P.

The Chummy FourAccumulators

ALTHOUGH it does not appearat first sight to be essential to

use unspillable accumulators in theChummy Four, as the set is carriedand operated in an upright position,yet the use of C.A.V. batteries hasone very great advantage.No Acid Fumes

These batteries have an electro-lyte of jellied acid, which obviates atonce any possibility of acid fumescorroding other components, such asthe cone loud -speaker, in the vicinity.

This is a point of some importance,and is the reason why C.A.V. jellied -acid accumulators are essential forthe Chummy Four if it is to remainin perfect working order as long as itshould.

Remember that for the ChummyFour you need two C.A.V. 2NS9accumulators and for the SidecarPortable a 2NS13 battery.

Full constructional details of theChummy Four were published in theJune WIRELESS MAGAZINE ; furthernotes appear on page 13.

fo4 44. V 4

The "Wireless World" says"We hope that other dry battery makers will follow Messrs.Ripaults' lead and come oat into the open with details ofthe average life which may be expected from their cells."-See page 978, May 2nd issue.

FACTS AND FIGURESThe figures shown on the table below in respect of a "High-clasa Ordinary Battery "are as a matter of fact identical with those which recently appeared Ma Trade Organ,and from the figures quoted it will be seen thatRIPAULTS' SELF -REGENERATIVE H.T. DRY BATTERIESLave very nearly doable the life of an ordinary high-class battery.

Capacity and Rate atwhich discharged

Useful Life Extra Given byterygenerative Battery Ordinary Battery

Standard CapacityDischarged at 5 111.8. 650 hrs. 320 hrs. 280 hn.Double CapacityDischarged at 10 m.a. - 475 hrs. 260 hrs. 215 hrs.Treble CapacityDischarged at 15 ma. 600 hn. 280 hrs. 220 hrs.

STANDARD - 60 volt, 10/6 ; 99 volt, 16/8. DOUBLE . 60 vol , 15/8 ; 90 volt, 22/6TREBLE - 60 volt, 19/6 90 volt, 29/6

RIPAULTS LEAD IN LIFE, EFFICIENCY AND VALUE.How do we obtain more than It volts per cell? Many Technics Experts will tell youthis is impossible and yet, for example, our 60 volt models contain only 90 cells andthe total E.M.F. is approximately 64 volts. The common practice of includingadditional cella to bring up the voltage is misleading unless the purchaser is warnedthat a Battery containing, for example, 44 cells should give a reading of not less than66 volts, otherwise deterioration hes already commenced. Write for "Ripaulta ""Life Chart" and "Right Choice" table W/M99 with full range of voltages and prices,also complete copies of technical Press "teat" reports. Obtainable from all Dealers.

RIPAULTS LTD.If any difficulty locally write us.

, 1. KINGS RD., LONDON. N.W. I

68

The idealsmall capacity

CondensersThese two Igranic Micro Con-densers have become almostthe standard where small vari-able capacities are required-the Panel Type where frequentadjustment is necessary and theBaseboard Type whereit may be left overlong periods. Both havethat smooth, even actionso essential for fine ad-justment and both aredesigned to eliminatehand -capacity effects .Their maximum capacityof 38 mmfds. is the idealvalue for all purposes forwhich they are intended.Write to -day for List No. J589,the complete Igranic Catalogue.A free copy of "Selected Circuits"by H. J. Barton Chapple, B.Sc.,

will also be sent you.

OrrrECTRi _

The Igranic Micro Condenser.Baseboard Type.Price 4/ -

The Igranic Micro Condenser.Panel Type.Price 5/6

149, Queen Victoria Street, LONDON, E.C.4.Works : REDFORD.

BRANCHES:Manchester, Birmiagnam, Cardiff, Leeds,

Newcastle, Bristol, Glasgow.

LAAAVVAIA/VAAkAVim/dli

WE' 'ITCOA.IPOWE TSAre Absolutely Guaranteed

THE WEARITE CHOKEas used in the

" PILGRIM PORTABLE "has such a firmly established reputationthat it needs no further introduction.

Price 6/6THE WEARITE

ANTI -CAPACITY SWITCHas used in the

" CONNOISSEUR'S SIX "Double -pole Change -over Type.

Price 6 -WRIGHT & WEAIRE LTD.,

740 High Road, N.17.Phone Tottenham 3132. Wril to for Fres Lists.

DON'TGRUMBLE'AT THE

ENDFLUXITE SOLDERING 7/6SET - - completeor LAMP only - 2 6

FLUX Iirgsimplifies soldering

All Hardware and Ironmongery Stores sell FLUXIIE. intins, prices 8d., 1/4 and 2/8. Another use for Fluxite-

Hardening Tools and Case Hardening.Ask for leaflets on improved methods.

FLUXITE LTD. (Dept. 332) Rotherhithe, S.E.1 6


ADJUSTABLE SPINDLE OF INSULATING MATERIAI

THE"CONNOISSEUR'S

SIX" INCORPORATESTHESE BURNDEPT

COMPONENTSSEE PAGE 20 OF THIS ISSUE OF "WIRELESS

MAGAZINE."If you're going to build the " Connoisseur's Six " youwill do well to use the components utilised by thedesigner, who specifies three BURNDEPT Log LawCondensers and three BURNDEPT Ethovernier Dials.Once again proof that BURNDEPT Components areinvariably chosen by acknowledged radio experts.BURNDEPT Condensers are chosen because they areabsolutely free from hand -capacity and give increasedsignal strength, whilst Ethovernier Dials are preferredbecause they make tuning a simple matter. TheEthovernier Dial will fit almost any condenser : it has an18-i reduction for fine adjustment, and is free frombacklash. If you build the "Connoisseur's Six"-or anyother set-see that you use BURNDEPT Variable Con-densers and Ethovernier Dials for the very Lzst results.

69

BURNDEPTVARIABLE CONDENSERSand ETHOVERNIER DIALS

Offices - - BLACKHEATH, LONDON, S.E .3London Showrooms, 15, BEDFORD ST., STRAND, W.0 .2

LOG LAW CONDENSERS : .0003 mfds.,Price 15/-, .0005 mfds., Price 15/6.

(For these Condensers printed wave -length scales,range 150-3,000 metres, can be obtained for use

with closed circuits, Price 1/6 per set).SQUARE LAW CONDENSERS: .000crimfds., Price 13/6, .000i mfds., Price 13/6.

(None of these Prices include Dial or Knob).ETHOVERNIER DIAL: with Ethologand card scales for recording stationsettings, REDUCED PRICE 6/- each.

MM.*

\17VANTAVIAN1PSCSIV4.i

nWireless Magazine, August. 192:91

"W.M." Tests of New ApparatusConducted by J. H. REYNER, B.Sc., A.M.I.E.E.

PHILIPS' L .F . TRANSFORMER

Philips' Low -frequency Transformer

A SMALL and reasonably light low -/IL frequency transformer has been thedesire of many set constructors, particu-larly those who have made portable ortransportable receivers.

Hitherto, we have usually associatedthe ultra small and compact transformerwith the second-class apparatus, sinceit is difficult to visualise a high induc-tance primary winding, which means alarge number of turns and an iron coreof ample dimensions, in anything but abulky component. Recent research, how-ever, has shown that instruments can beproduced having good performance withsmall dimensions.

The new Philips' low -frequency trans-former which we recently tested hasover-all dimensions of 31/2 in. by I in.by 2 in., and is, therefore, considerably

smaller than the majority of transformerson the market.

Measurements taken in our laboratoriesindicate that the inductance, with a smallpolarising current through the primarywinding, lies between 45 and 5o henries,although the step-up ratio is 3 tor. Themakers claim that such figures areobtained by the use of special materialsboth in the windings and iron core.

The base consists of a well -finishedinsulated moulding on which four ter-minals and soldering tags are mounted.The transformer is enclosed in an ironshroud having a crystalline blackfinish. Philips Lamps, Ltd., of 145Charing Cross Road, W.C. 2, are themakers.

EDISWAN LOUD -SPEAKERTHE Ediswan One -der loud -speaker,

which has been submitted for testand report, has a striking appearance,owing to the large size flare and brownfinish given to the model. The import-ance of a large -size diameter horn is notalways realised, yet reproduction isgoverned to a great extent by the designof the horn. A large flare such as fittedto the One -der loud -speaker helps inobtaining a better reproduction of the

low notes and also assists by reducinghorn reflection and preventing resonance.

Another quality of this loud -speakeris its sensitivity to weak signals. It willreproduce at comfortable strength anelectrical output, which would, with many


Ediswan One -der Loud -speaker

csmai NON -SPILLABLE25:Vi THE MOST COMPACT

ACCUMULATORFOR ALL

PORTABLE SETSThis battery, chosen by the " Wireless Magazine "for use with their remarkably successful Portablereceivers, the " Chummy Four " and the " Sidecar Port-able," is also included in the design of the "PilgrimPortable" described in this issue.This battery is not only non -spillable, but the speciallysolidified electrolyte remains undisturbed whatever theangle of the set. When most types of unspillable cellsare placed at an acute angle the free acid uncovers andexposes the surfaces of the plates, causing the storedcharge to be lost to the user, whilst the exposure is alsoseriously detrimental to the life of the battery.Obtainable from our Depots, Agents, or from WirelessDealers everywhere.

CUT OUT AND POSTPlease send

descriptiveliterature o fyour Non -Spil-lable Batteries ADDRESS_and name ofnearest agent

L who can supply

NAME_

TYPE 2 NS 92 VOLTS, 11 AMP. HRS.

Weight 2 lb.

SUPPLIEDFULLY

CHARGED 12/6

TYPE 2 NS 132 VOLTS, 16 AMP. HRS.

Weight 21 lb.

SUPPLIEDFULLY

CHARGED 15/-'Grams-

, J g. Chiswick 3 8ca'Phone:

Vanteria, Act, ACTON. LONDON, P3,. (Private BranchLondon." Exchange).SALES AND SERVICE DEPOTS AT BELFAST, BIRMINGHAM,BRISTOL, CARDIFF, COVENTRY, DUBLIN, GLASGOW,

LEEDS, MANCHESTER AND NEWCASTLE.

70

rERRAn TTHE SPEAKER WITH

THE EXPONENTIAL HORN

THE BEST SPEAKERfor

THE ORDINARY SET


x'63at-,_---FERRANTI LTD.

HOLLINWOOD, LANCASHIRE II

AS SPECIFIED FOR"PILGRIM PORTABLE"

PEERLESS" RESICON"CONDENSERS

are specified because ofthe greater tuning rangethey pros ide and the ex-tremely smooth adjust-ment. Whatever circuityou are building, askyour dealer for Peerless

Resicon " Condensers ;if he cannot supply senddirect to us.

PRICE

(without dial) .00025.0003 12/6.0005

PLAIN KNOB DIAL - - 1/6THE BEDFORD ELECTRICAL & RADIO CO., LIMITED, 22 Campbe:I Road, Bedford

LONDON: 21 Bartlett's Bldgs., Holborn Circus, E.C.4. GLASGOW 113 St. Yincent Street, C.2

SPECIFIEDBY COSSOR

The W.B. Antiphonic Valve Holder isbeing specified more often than any otherin the best circuits of the radio journals.The greatest success of the season-theset that thousands have built and thous-ands more are building, the CossorMelody Maker, definitely specifies W.B.Antiphonic Valve Holders.You will appreciate the absolute freedom

from microphone noises of the valvefloated on the W.B. valve holder springs.From all good dealers.

PRICE 1/9 EACHwith terminals, or 1/6 without terminals.

WHITELEY BONEHAM & CO., LTD.NOTTINGHAM RD., MANSFIELD, Notts.

71

TEMPRYTES

To LT,

PRICES: Ten, prytes1/6. Mounts 1/-. short-ing Plugs 6[1. Statemake and type ofValves used, or s, rite for" Temprytd" Chart, freeon request.

SYDNEY S. BIRD & SONS, LTD.CYLDON WORKS - - - ENFIELD TOWN

CABINETS

For

Moving CoilSpeakersPortables

orAny Circuit

fOr rule el 1 esf (r

Carrington Manufacturing Co.Ltd., Camco Works, Sander -stead Road, South Croydon.

'Phone: Croydon 0623 (2 lines)


"W.M." Tests of New Apparatus (Continued)speakers, be insufficiently audible.

As an approximate test on the per-formance of this speaker, we connectedit to the output terminal of an electricaloscillator capable of producing audiblefreqUencies from a few cycles per secondup to 6,000 cycles at constant amplitude.At certain frequencies there was evidenceof slight resonance in the speaker and aslight falling -off in volume at frequenciesbelow 30o cycles per second. On thewhole, however, the speaker performedwell and gave quite pleasing reproduc-tion of speech and music when tested ina broadcast receiver.

As regards mechanical details, thehigh -resistance windings are placed ontwo bobbins, fitted over a substantialsteel magnet, over which a large dia-meter diaphragm rests. The positionof the magnets relative to the diaphragmmay be adjusted by means of a smallgrub screw operated from the side of thebase; The speaker can be recommended.

The manufacturers are The EdisonSwan Electric Co., Ltd., of PondersEnd, Middlesex.

BURNDEPT PICK-UPTHE gramophone pick-up has added

a new interest to wireless since ithas enabled gramophone records to bereproduced with remarkably good tonal

quality in conjunction with a properlydesigned low -frequency amplifier andloud -speaker. In addition, the volumeof reproduction may be readily controlledby means of a variable resistance placedacross the pick-up.

It is only natural that first-classreproduction should depend on the type

Burndept Magnetic Pick-up

of pick-up aniplifier and loud -speakeremployed; disappointing results willoften occur if one of these items is incor-rectly designed.

We have received for test a Burndeptelectric pick-up. This component bearsevidence of careful workmanship and

design. The magnetic unit consists of avibrating armature held centrally in anelectrically balanced position betweenthe poles of an electro-magnet. Actualcontact between the armature and thepole pieces is prevented by means of asubstantial rubber washer fitting overthe armature, which is clamped to give

the correct degree of damp-ing.

With all types of gramo-phone pick-up, it is ofextreme importance to allowappreciable lateral move-ment of the armature inorder that the needle mayfollow the vibration ridgesset up in the record. If thearmature is too stiff, rapidwear of the record willensue: on the other hand,should the damping be toolight, forced vibrations maybe set up with consequentdistortion.

In the Burndept pick-up,a happy medium seems to

have been reached with respect toarmature damping and the resultsobtained on test in our laboratories,indicated that the makers have producedan instrument which gives good repro-duction, is sensitive and free fromchatter.

"OF PROVED EFFICIENCY"BUILD THE

PERMANENT- MAGNET

MOVING -COIL SPEAKER(Requires no Accumulator)

Described in "WirelessMagazine," June, 1928

£6 5 0 completeWrite for Lists

Manufactured by

BAKER'S SELHURST RADIO,42 Cherry Orchard Road, East Croydon.

'Phone: CROYDON 1618.

ParfaitBRAND 1=111

THE PERFECT EBONITEIN SHEETS or PANELS. Made in SIX Qualities:MATT. SEMI -POLISHED BLACK. HIGHLY -POLISHED BLACK. SEMI -POLISHEDMAHOGANY. HIGHLY -POLISHED MAHOGANY.

HAND -POLISHED BLACK (both sides).Sole Manufacturers :

H.B. POTTER & CO., LTD.,STATION BUILDINGS :: ROCHDALE

WORKS: DUKE STREET, ROCHDALE

FORITO-patiuR PREEN 84 CO LTO

PRICES

.0005 5/.

.00035DUAL GANG

15/6TRIPLE GANG

El : 1 : 0

"1928" LOG CONDENSERAs specified for the

"CHUMMY FOUR"DESCRIBED IN " W.M." JUNE ISSUE

The SMALLEST, LIGHTEST andmost EFFICIENT CONDENSER

obtainableTHE FORMO CO., Crown Works, Cricklewood Lane, LONDON, N.W.2.

72

SPAN FULLY OPEN

WEIGHT

OUNCES

BENI ND PANEL

"

Comments on the Five -

pounder Four Full Constructional Detailson Pages 5-9 of This Issue

THE Five -pounder Four was notthe outcome of a bet, although

when I first heard of the intentionexpressed by the WIRELESS MAGAZINEStaff of producing a four -valve re-ceiver at that price I doubted verymuch whether the set would becapable of doing what was asked of it.I tender my apologies; I have had thereceiver on test for several days andhave been surprised at the resultsobtained.

Value for Your MoneyThere appears to be little doubt

that at the cost of some five poundssterling for components you can con-nect up almost nightly with fromfifteen to twenty stations withoutencountering any difficulty ; for theoutlay of five "Fishers" you mayvisit in turn England, Austria,Belgium, Denmark, France, Germany,Holland, Hungary, Italy, Poland,Spain and Sweden, with a sportingchance of hearing transmissions fromother countries even more distant.

The tone and volume on a coneloud -speaker were very satisfactory;in fact, for the more powerful stationsslight detuning was found necessary.Its selectivity is particularly good,but to facilitate tuning it would bewise to equip the anode condenserwith a slow-motion dial.

Coils to UseFor the broadcasting waveband, a

No. 6o tapped coil was used, butthe range would be extended if forlower wavelengths than 30o metresa smaller aerial coil were .adopted.For the long waveband both a No. 100


or a No. 15o and No. 200 tapped coilswill be found necessary.

The log of stations given on page 9.was compiled on three separate even-ings and as an instance of the Five-pounder's reliability I need onlymention that in each instance Buda-pest, Milan, Vienna, Kattowitz, andCopenhagen were received on theloud -speaker.

Stuttgart was obtainable when 2L0was working and so soon as the latterstation closed down -my house iswithin miles of the London aerial-loud signals from Leipzig werepicked up. Some little difficulty wasexperienced in separating Brusselsfrom Vienna but this was overcomeby more careful adjustment of theneutralising condenser and a conse-quent improvement in reaction.

How to Adjust ReactionTo permit of the reception of distant

stations it is essential that the reactioncondenser should be adjusted justunder oscillation point; any kind ofharsh reaction will prevent goodtuning apart from the production ofdistorted howls, whistles, and otherunpleasant noises which worry bothyour neighbours and you. As an all-round four -valve receiver capableof being built at a low cost andpossessing the advantages of manymore expensive sets, the Five -pounderFour can be strongly recommended.

I have handled many receivers whichcould not compare with it, although,in most instances the price asked forthem was at least double its primarycost.

J. GODCHAUX ABRAHAMS.

A Show(room) Worth SeeingREADERS of the WIRELESS MAGA-

. ZINE who have walked downKingsway recently will have noticedthe very striking window display inconnection with the new R. I. andVarley showrooms at KingswayHouse, 103 Kingsway, W.C.I.

For the benefit of those readerswho have not yet visited these show-rooms we may say that this is a displayof all the products marketed by R. I.and Varley, Ltd., and is arranged tointerest wireless enthusiasts and notfor the direct sale of components.

Readers who have the opportunity

should certainly visit these rooms,where they will not be pressed or evenasked to buy, but will be given anytechnical information they may re-quire about the use of R. I. & Varleycomponents in their receivers.

Those who are unable to visit theshowrooms will find it well worthwhile to apply for the handsome 24 -page catalogue for amateurs issuedby this firm. Mention the WIRELESSMAGAZINE and address your inquiryto Sales Department, R. I. & Varley,Ltd., Kingsway House, 103 Kingsway,W .C. .

73

K. RAYMOND27 & 28a LISLE STREET, LONDON, W.C.2

Come to Leicester Square Tube.This address is at the back of Daly's Theatre

'Phones : Gerrard 46.17 and 2821.

Orders despatched same day as re-ceived where possible. Send ORDER

CEOs D with instructions and pay Postman.

WE ARE OPENALL DAY SATURDAYALL DAY THURSDAYALL DAY EVERY DAYHours : 9 a.m. to 8 p.m.Sat.: 9 am. to 9 p.m.Sunday morning : 11-1.

Quotations forall circuits.

Special Prices on lists ofparts over 20 - value, forcallers or post orders.

FIVE -POUNDER FOUR(W.M. August, 1928). SPECIFIED COMPONENTSTwo Raymond Special L.L. Condensers, .0005(with 4 -in. dials) (used in set), at 5/11 each. Bulgin.0001, 5/8. Liman Pan. Rheo., 2/6. Coil Stand,1/-. Bulgin Neutralising, 5/-. Four Anti -micro.V.H. at 1/3. Six -pin Base, 2/-. Lissen .0003and 2-meg., 2/-. Lissen H.F. Choke, 5/6. Do.,R.C.C. Unit, 4/-. L.F. Transformer, Igranic, 18/ -(or R.I. & Varley, 15/-). Ten Engraved Ter-minals at 6d. each. Drilled Strip, 1/3. TwoIndicators, 4d. Ebonite Panel, 1C x 8, drilled, 6/-.Connecting Wire, Screws, and Baseboard, 2/6.

The above Lot, £ 3 6s. 6d. U.K.SEND NO MONEY. PAY THE POSTMAN C.O.D.We Pay all charges on above. Please Write

Plainly.Coils for above, Lewcos 60 C.T., 3/6 ; 150 C.T., 5/3Binocular 6 -pin S.P.H. F.T. (B.S.P.5), 10/- ;B.S.P.20, 12/-. Handsome American -type Cabin-et, 16 x 8 x 9, 12/6. Carriage 1/6.

Mast Clear, owing to new design being shortly placed on themarket.

THREE -VALVE LOUD-SPEAKER SETS

Gets London, and amuirtn

D. & 2L.F.

LIMITED

NUMBER

Call and

hear one

demon-

strated.Bet, with 3 Dull -emitter Valves (1 Power) andTuning Coils (Tax Paid), as shown In OakAmerican Cabinet. Switch for 2 or 3 valves,parts enclosed. SPECIAL CLEARING OFFERBatteries, Aerial, and Speaker extra.

Carriage Paid to Addresses in U.K. for 85/, or C.O.D.Orders for Abroad or outside U.K , additional carriage and

packing, Insurance, etc., must be included.

H.T. BATTERIES. Special West End distributor of Riyault'sBatteries. The H.T., 99.v., 18/6. Lists Free.

HELLESEN'S H.T. BATTERIES. Prices reduced. Qualityunbeatable. 60-v. now 10/6. 99-v. now 18/-. Also 1.5,4-v., 9-0., 16-v. stocked.

LOSER, 60-v., 7/11 ; 100-v., SIEMENS' --still top of the12/11. Super, 60-v., 13/6 ; tree. 60-v., 8/8 ;

Grid Bias, 1/6 ; 4.6, 51- dos. 14/-. Power, 60-v., ;

EVER READY, 60-v., 7/- ; 10-v., 8/9 ; 9-v., 2/-.66-v., 9/8 ; 99-v., 11/8. Popu- OLDHAM LT, 8-v.,,43, 8/. ;lar, 60-v. 8/8 ; 108-v., 15/8. 2-v., 80, 15/-.

Flash Lamp, 6/- doz. Flag =ME AND ALL MAKES1.5 stocked. Grid Bias, 9-v.,1/8. STOCKED.

SENT C.O.D. PAY THE POSTMAN.

OOSSORMELODYMAKER

Specified parts, withCoesor Wound Coil,

le 10s. W.FREE WITH ABOVEDrilled Polished Panel,21 x 7, Drilled Strip, etc.

MILLARD MASTER 3

Specified parts, with Coilsand 3 Valves, SA 17 8.

FREE WITH ABOVE KITExtra quality aluminiumPanel,18 a 7, drilled (surfacespecially frosted); 9 -volt GridBias; 100 -volt H.T. (goodmake), OR you can have OakCabinet, 18 x 7 binged lid,American type, instead ofH.T. Battery. Carriage 2/6.

Full details of above free, or see recent issues"Amateur Wireless" and "Wireless Magazine"LISTS AND LEAFLETS FREE. LONDON'S LEADINGDISTRIBUTOR OF COMPONENTS, ETC., MADE BYIgraine, R.I. & Varley, Bowyer -Lowe, Wearite, Watmel,Buigin,Lissen, Letveos, Mullard, Cossor, Ediswan, Cosmos, Marconi,Ormond, " J.B.," Dubilier. Ampliou , etc.


CONTRThe flickering needle of the telegraph wavers. . . then like a live thing darts forward . . .the pulsing engines strain and throb . . . slow-ly the great ship gathers speed to race onthrough the night . . frantically the sensitiveneedle oscillates, then settles down . . . with aswirl the propellers whirl in reverse, thedanger is averted . . . perfect control hasplayed its part. Slowly the needle rises . .. 60

. . . 70 .. . 80 . . . 82 . . . then falls to 80 ... withuncanny purity the voice of a wonderful con-tralto is wafted into the room . . . the Brownssettle back in comfort . . . their evening'spleasure is assured. Again control, sym-bolised by a Sifam Radio Meter, has played itspart.

RADIO METERSSend for "DetectingDistortion" free front81F4it, LTD., Bush

House, Aldwych, W.0.2.(Mention Debt .11

SIFAMELIMETER

200 -volt forEliminators3at-

POCBETVOLTMETER

120 -volt. 4,000ohms Res.MO 9/611

.4111EIMM. B. III

Uri .EEMX:112

"TREBLE DUTYTERMINAL,'

AMP, 07MER, WIRELESS ACCESSORIESJ.J. EASTICK SONS,

EELEX MOUSE. DUNHILL ROW., LONDON, E.C.I.

7akingtheVOutoftlfrelessi

By John SimpleThis is the second of a number

of elementary articles by a" low -brow " amateur writing inthe" Wireless Magazine " underthe name of John Simple. Fromtime to time he will tell readersof his practical experiences withdifferent types of sets and specialpieces of apparatus in an informa-tive yet chatty way; this month hewrites about tracking troublesin receivers.

Beginners and other amateurswho have not had much practical

WHEN I suggested to the Editorof the WIRELESS MAGAZINE

that I should be pleased to have anopportunity of unravelling some ofhis readers' knotty problems atgreater length than the TechnicalStaff probably have time to give toindividual questions, I hardly ex-pected to be at once confronted withso difficult a problem as that set byan amateur in North Ferrily, Yorks.

Trouble with the 1927 FiveAfter explaining that he had built

up the Music Charmer with veryexcellent results and that it is admiredby everyone who sees it, this readersays that he built some time previ-ously a 1927 Five receiver, on whichhe has been able to receive only 5GB,5XX, Hull (local), Manchester, andabout two other stations. Can I tellhim what is wrong?

Well, at once let me say quitefrankly that I cannot, but I can makea few comments which I hope willhe of value to other amateurs as wellas to this particular inquirer.

From his letter I gather that he hasalready written to the WIRELESSMAGAZINE Technical Staff on several

experience in radio will find JohnSimple's " confessions " bothinteresting and helpful, for hewrites with the understanding ofone who has just passed out of thenovice stage himself.

If there is any special pointabout the operation of a set thatis at present obscure to you, justdrop a line to John Simple. Hewill try to answer any practicalquestions in his articles, but hecannot undertake to do so by postindividually.

occasions regarding this set andreceived advice. He complains thatthe same reply is given almost everytime and that even when he hasapplied the suggested remedies nobetter results are obtained. Alto-gether I gather that he is prettyfed up!

Now the point that strikes me atonce is that the information con-tained in the letter is far too indefinitefor even the most experienced tech-nician to say at once what is wrong.Failing exact details of all the symp-toms, it is only possible to generalisevery widely, as there are such anumber of things which might becausing trouble.

The Case in DetailLet us examine the case of this

1927 Five in more detail. In the firstplace the aerial is of the twin type,the wires being spaced 6 ft. apart,while it is 4o ft. long. Two -voltMarconi valves are used, and thehigh-tension supply is obtained froma Clark's Atlas eliminator. The wir-ing has been checked and found cor-rect, all the connections are good, andthe constructor has been told that

clAROSTP:c CLAROSTgirammrs

The Regal Range of Resistances!There is a " GLAROSTAT " for every resistance purpose, each thelast word in neatness and efficiency. Made in the following types :-

POWER ClarOstat. GRID LEAK ClarOstat,STANDARD ClarOstat, VOLUME CONTROL ClarOstat.(rating 40 and 20 watts- TABLE TYPE ClarOstat,chiefly for eliminators). (" A distant control of Volume.")

From on Pad dealers; to ease of difficulty we supply directLiterature on whole range 7555 and POST FEES

CLAUDE LYONS, Ltd.. 76 Old Hall St., LIVERPOOL

BeautifullyMade.

MicrometerAdjustment.

74

"it is a beautifully built set."A rheostat is provided for each

valve, while the condensers areJackson's, with slow-motion dials.The windings of the anode coils havebeen changed several times.

Excellent QualityOne might suppose that after all

this trouble the constructor wouldfeel like scrapping the set, but hedoes not wish to discard it because ofits good appearance and the excellentquality of the few transmissions thathe can receive.

Bellcore attempting to suggest anyremedy for the state of affairs thatexists, one would like to have muchmore definite details of the symptoms.For instance, there is no indication asto whether the set oscillates violently,or not at all; whether neutralisationcan be carried out; and, further (athing that is of the utmost importanceto the would-be adviser), no mentionis made of the actual types of valvesused.

With such limited knowledge of theactual conditions it is extremelydifficult to attempt a satisfactoryThe 1928Five

Two H.F.,Detector andTwo L.F.

diagnosis of the real trouble.In the first place I should like to

suggest, however, that the aerialwould be much better if it consistedof only a single wire, 4o ft. length,instead of the twin arrangement. Asit is at present, the aerial is likely tohave quite a large capacity, and thisis always undesirable. Better resultsin all probability would be obtainedby inserting a small fixed condenserof the order of .000s microfaraddirectly in the aerial lead.

Having made that addition, if Iwere testing the set, I would take alead from the grid of the first high -


frequency valve to the grid of thedetector valve and switch out boththe high -frequency amplifiers.

Then I should try out the set tomake quite sure that both low -fre-quency stages were doing their propershare of amplification. This is madeeasy by the fact that a jack is pro-vided for cutting out the last stage.A point I should give special con-sideration to is that no reaction isincorporated, and therefore I shouldnot expect to get results such aswould be obtained from a normalthree -valve set with a reaction con-trol.

H.F. Stages in TurnHaving satisfied myself that the

low -frequency stages were O.K., Ishould next remove the temporarylead from the grid of the detectorvalve and place it on the grid of thesecond high -frequency amplifyingvalve, replacing the second valveand switching it in circuit.

I should now try the neutralisingarrangement to see that it was operat-ing properly and, if it were not, Ishould then make the -ecommended

Described inJanuary" W. M."

BlueprintNo.W.M.46,price is. 6d.

alterations to the coils until I wascertain that the high -frequency stagewas doing all that it ought. Thiswould have got four valves workingproperly, and I should then alto-gether remove the temporary gridlead referred to and put the firsthigh -frequency valve into operation,again making sure that its neutralis-ing was perfectly O.K.

Inspecting Coil ContactsIn going over the high -frequency

coupling coils I should carefullyinspect the pins and sockets to make

(Continued on next page)

75

Whatever kindof set you use... look to the valve holders.If they are Lotus, they are bestfor your set. They will pro-tect your valves from shocks,prevent irritating microphonicnoises, and ensure pure, clearreception. Owing to the socketsbeing split, they expand on in-serting the valve legs, and thusgrip the legs throughout thewhole socket depth. Thevalve cannot work loose.

Whether you buy your set ormake it yourself, insist on

Lotus Valve Holders.

From all radio dealers at 1 /6 without

terminals, 1 /9 with terminals.

"onusVAD4:1A-O.PER

Made by the makers of the famous Lotus RemoteControls, Lotus Vernier Coil Holder, and Lotus

Jacks, Suitches amd Plugs.

GARNETT, WHITELEY & CO. LTD.,

Lotus Works, Broadgreen Road, Liverpool.


The Finest GiftAs a gift " Celestion," mostexcellent of Loudspeakers,is without a peer, for all whohear it can share the greatpleasure that it brings. Getyour dealer to demonstrate" Celestion" for you. Youwill be amazed at its realism.

Embodied in "Celestion "are the six essentials ofan excellent Loudspeaker.

They are-EVEN RESPONSE

EXTREME SENSITIVITYONE ADJUSTMENT

IMPERVIOUS TO CLIMATEIMPROVEMENT WITH AGEDISTINCTIVE APPEARANCE

Moreover, "Celestion" isBritish made throughout

(Made under Licence)

There are four " Celestion "models in oak or mahoganyranging from £510s. to £25. Weshall be glad to forward to youour free illustrated literature giv-ing full particulars, and of our" Woodroffe " Type GramophonePick-up. When ordering thePick-up please state whetheradaptor is for H.M.V. or in. size.

CELESTION"C'he Very Soul of Music

Write to Dept.

THE CELESTION RADIO CO.Hampton Wick, Kingston -on -Thames.

Showrooms :33/35, VILLIERS ST. - LONDON, W.C.a

Associated Company :CONSTABLE-CELESTION CO., PARIS

Taking the "Ire" Out of Wireless (Cont.)sure that they were making perfectcontact. I should also try variousvalues of grid leaks and-this beingas important as anything-a criticalvariation of the high-tension vol-tages applied to the various stages.

A systematic test of the set onthese lines is certain to result in thetrouble being found. In some cases,of course, it is due to a faulty com-ponent, and troubles in this directionare sometimes not at all easy to trackdown.

These remarks will, I hope, bebeneficial to many WIRELESS MAGA-ZINE readers, but in particular to thisquerist regarding the 1927 Five.There is one thing I should like topoint out to him about this set, andthat is that it is now rather out ofdate. As long ago as last January theWIRELESS MAZAZINE published de-tails of a revision of this receiverunder the name, "The 1928 Five."The chief difference between this andthe old 1927 Five is that reaction isincorporated.

If all else fails, I would recom-mend to this reader that he shouldconvert his set into the 1928 Five,when I am sure he will be able to getthe stations he desires.

When You Want AdviceWhenever they are asking queries

on paper about elaborate sets of thistype readers should always give thefollowing information to those whoseadvice they are asking :

I. General characteristic of aerialsystem.

2. Details of types of valves used.3. Actual anode and grid -bias vol-

tages applied to the various stagesand, in the case of the former,whether obtained from an eliminatoror batteries.

4. In the case of high -frequencyamplifiers, whether there is troublewith oscillation and whether or notthe stages can be satisfactorily neu-tralised.

5. Where reaction is incorporated,whether no oscillation is obtained atall or whether oscillation is too fierce.

6. Whether the components usedare exactly the same as employed inthe original receiver and, if not, whatparts have been substituted, withdetails of the manufacture andvalues.

76

Usually there are so many thingsthat might be wrong with a wirelessreceiver when it is not giving theresults that are expected from itthat it is almost impossible to give asatisfactory reply on paper unless allthese details are available.

Value of ExperienceIt is a fact, though, that when one

has had a little experience in handlingdifferent types of receivers one seemsinstinctively to know what is wrongwhen one can operate the set oneselffor a short time without goingthrough the whole process of reductioad absurdum which I have outlined.

If these hints enable the reader atNorth Ferrily to overcome the troubleI shall be glad to hear from him,while if he still cannot get results andcan give more definite symptoms ofthe difficulty, I have no doubt thatthe WIRELESS MAGAZINE TechnicalStaff will be able to give him a satis-factory reply by post, but that I amunable to do myself.

THE SAME OLD SONGSSINGING being one of those things

which all of us can do, more orless, we take a great interest in thevocal items put on by the B.B.C.

When it comes to the songs ofSchumann (which are some of thebest ever written), the low -brows willbe out of their element; but they-perhaps I should say "we"-arenot always satisfied with the morepopular efforts sometimes broadcast.Possibly because there really are notmany popular songs suitable forbroadcasting we hear the same olditems over and over again.

This is not a complaint, but a regis-ter of fact.

How often within the last monthhave you heard, " Come to the fair," orvarious settings of the LondonderryAir? These are only two of the manyexamples which might be cited.

Unfortunately, there is no properremedy. The B.B.C. can't producenew songs and song -writers by wavinga magic wand. And the broadcastinghours must be filled with music andsong of some kind.

Oh, that another mass -productioncomposer like Schubert would ariseand give the announcers somethingfresh to announce P. B.


Modified H.F. Coupling Unitfor the Sunshine Five and Sidecar Portable

EXPERIENCE has shown that thePolar two -stage aperiodic high-

frt q iency coupling unit could bealtered with advantage, and we learnfrom the manufacturers that the oldtype of unit is now withdrawn and isreplaced by that illustrated below.

This new component is supplied ina moulded case and does not includevalve holders. There are four ter-minals in place of each of the existingvalve holders, to which the filament,grid, and anode sockets of any suit-able valve holder may be connected.

Suitable Valve Holder to UseAn Ashley valve holder is recom-

mended; this holder consists of acentre portion carrying the fourvalve sockets, thisbeing floated in acircular base. Thetwo parts areheld together byfour screws,which also serveacs terminal con-nections.

On removingthese screws, thecentre portion,with four springconnections at-tached to it,comes away completely and can beplaced over the four terminal screwsof the unit, which will be found to fitthe valve holder exactly. Replacingthe nuts and terminal screws com-pletes the assembly.

Valve holders assembled in thisway are vibratory, so that tendencyto microphonic noise is lessened.

Positioning StopsUnderneath the anode and grid

terminals of the valve holder will befound two small metal stops, whichlap over a rim moulded round thebase of the centre portion of thevalve holder. The function of theseis to prevent the holder from beingpulled out of position when the valvesare removed. These stops should bereplaced in their appropriate posi-tions when the holders are fitted tothe unit.

The terminals GI and A2 whichwere on the original unit are nowomitted, the connections going direct

Modified Polar H.F. Coupling Unit

to the grid terminal of the first valveand the anode terminal of the secondvalve. In addition, there is a slightmodification in the arrangement forstabilising the unit, which has beenmade possible by the fact that thesecond grid is now provided with aterminal, and is, therefore, availablefor external connection.

Neutralising CondenserIn the original unit, a stabilising

condenser was provided between thegrid of the second valve and the gridof the first valve. Experience hasshown that this stabilising connectionis only necessary on the long wavesand that it is desirable to cut it outon the short waves. A small neutra-

lising' condenser-anystandard typewill do, althougha small size ismore conveni-ent in a portablereceiver-shouldbe connectedbetween GI andG2 externally tothe unit, andconnections tothis should betaken throughthe ordinary

switch employed for changing overthe connections on the frame, in sucha manner that the neutralising con-denser is cut out of circuit in theshort-wave position.

Complete instructions as to howthis may be accomplished are givenwith a leaflet accompanying the unitand a full diagram of connections isprovided.

The neutralising condenser shouldbe adjusted to give adequate stabi-lity on the long -wave position. Itwill then be found that the short-wave position is inherently stable andthe reaction demand on both wave-length bands will be found approxi-mately the same.

The new unit, therefore, possessesimportant advantages, and the modi-fications required to existing dia-grams and receivers which incorporatethe old unit is only quite small. Thenew "All -wave Coupler" sells atLI 19s. 6d., instead of 2S., asformerly.

77

INN',St. WOUAlete. .4\

CR Al4 AM PetialSof

9 IEEE' NEW PRoC6S

GRID LEAKSPrice1 Megto 5 Meg -

"Undoubtedly the very finest Grid Leakmade at any price."

BAKELITE HOLDERS WITH

NICKEL TERMINALS FOR SAMEPrice 6d.

Of all Dealers or from

GRAHAM FARISHBROMLEY

KENT

THE PERFECTTERMINAL

For perfect design, finish and workmanship,Belling -Lee Terminals are unequalled.Chosen by all the leading Wireless Journals,and by manufacturers of sets and batteryeliminators.

PRICES:Type "B." Illustrated, sold in an attractive

carton carrying a year'sguarantee. Price 9d. each.

Type "M." As type " B," but non -insulated.Price 6d. each.

Type "R." Cheap competitive insulatedterminal with rotating name.Price Std. each.

Illustrated catalogue free on request.

BELLING -LEETERMINALS

Belling & Lee, Ltd., Queensway Werke, Ponders End, Al&

la


Bold the PILGRIM PORTABLE described I no nS. d.

1-Cabinet as described .. . 1 5 0I-Ebonite panel, 9 in. by 6 in. ready

drilled .. .. 3 0I-Peerless Variable Condenser, .0005-

microlarad .. 12 6

I-Peerless Variable Condenser, .0003-microfarad .. 12 6

2-Lotus Valve Holders .. .. 3 6

2-R. I. Varley Vernier Dials .. 7 6

-Lissen Fixed Condenser, .0003 . 1 0

-Lissen Grid Leak, 2-meg. 1 0

-Magnum H.F. Choke 7 6

-Philips L.F. Transformer 1 5 0

-On and Off Switch .. 1 6-Ripault 60 -volt H.T. (Chocolate label) 10 6

-C.A.V. 2 -volt Unspillable Accumulatortype 2NS9 .. 12 6

2-Belling-Lee Terminals as described .. 1 0

2-Valves as specified .. 1 1 0

£7 5 0

The above Portable can be supplied ready wired andtested, or any parts separately.

We specialise in - The Chummy Four," ready wiredor the kit of parts.

Send stamp for lists.OMNORA LTD.

Home Construction Specialists,858 NEW CROSS ROAD, LONDON, S.E.14

Phone: New Cross 1273

WEIGHT ADJUSTERREDUCES RECORD WEAR

(See Mr. Barnett's article in this issue).Fits any type of gramo tone -arm 7 / e Postwith swivel neck ... ... Price I U Free

H. L. WILSON 2;i 15 venue,Sh a' lel! ctlor ny

: Gramophone Specialist : W.C.2Write for List of -Slightly Used Records.

MOVING -COILLOUDSPEAKER

The "Zampa " is an entirely British instru-ment, scientifically and soundly constructed,unequalled In its quality of reproduction.Most economical to use as it only consumes.5 amp. at 6 volts. The moving Coil iswound to 1,500 ohms. Over-all measurementsare : Height Width 83", Depth 9".Remember the " Zampa " is a complete as-sembled unit. It gives absolutely natural,clean and crisp reproduction and yet is soldat the following low prices :

To work oft 6 -volt ac:umulator orTrickle Charger from A.C. Mains £6 10 0To work off D.C. Mains - £7 0 0

Obtainable Through all DealersIf any difficulty I ically, write to Sole Manufacturers:

MIC WIRELESS CO.White Horse Place, Market Street

WELLINGBOROUGHLondon Trade Sales Office ;

52 CRAVEN HOUSE, KINGSWAY, W.C.2

Wireless MagazineREFERENCE SHEETS

Compiled by J. H. REYNER, B.Sc., A.M.I.E.E.Month by month these sheets can be cut outand filed-either in a loose-leaf folder or oncards-for reference. The sequence of filing is

a matter for personal choice. In a short limethe amateur will be able to compile for himselfa valuable reference book.

WIRELESS MAGAZINE Reference Sheet No. 76

Inductances,THE design of an iron -cored inductance

differs somewhat from that of an air -coredcoil owing to the fact that the magnetic field isalmost entirely confined within the iron circuit.In this case, it is possible to determine the exactvalue of the magnetic flux with considerableaccuracy, whereas in the case of an air -cored

11 I;7-b-.;

Core type (left) and shell type (right)iron -cored chokes. Length of mag-netic circuit = 2 (a+ b), in each case

coil the lines of force stray by various routes andonly a small proportion thereof is actuallylinked with the turns of the coil. It is only suchmagnetic field 'as do link with the turns them-selves which is useful in producing inductance.

The inductance of an iron -cored coil dependsupon the square of the number of turns, and

Iron -coredupon the actual area of the iron core and isinversely proportional to the length of the ironcircuit. Two typical iron -cored choke coils areshown in the diagram. One is known as the" core " type and the other as the " shell " type.In the latter case, the thickness of the centreleg should be twice that of all the other portionsof the core.

Te actual length of the iron circuit is markedin the two cases and this must be evaluated forthe particular type of stamping used.

The inductance is also proportional to thepermeability of the iron which is really inter -linked with the other properties of the circuit.The expression for inductance is

L 1.257 An2µ100,000,000 I.

where L is the inductance in henries,n is the number of turns;A is the area of the core in square centi-

metres ;1 is the length of the magnetic circuit in

centimetres, andµ is the differential permeability for the

particular working conditions.

WIRELESS MAGAZINE Reference Sheet

Voltmeters, Increasing Range ofTT is often desired to increase the working'L range of a voltmeter so that the full-scaledeflection shall be higher than the normal. Thiscan quite easily be carried out by the additionof a suitable value of resistance in series with themeter.

A voltmeter consists essentially of a millia-meter in series with a high resistance. (SeeSheet No. 47.) The current flowing throughthe circuit, and hence the indication of themeter, clearly depends upon the voltageacross the whole and the actual resistance ofthe circuit.

In order to increase the range of the instru-ment, therefore, it is necessary to add resistance,so that for a given voltage the current will be lessand the indication on the meter smaller. Con-sequently, in order to obtain the full-scaledeflection a greater voltage must be appliedacross the terminals, which is what we require.

The voltage for full-scale deflection is directlyproportional to the resistance. If, for example,we wish to halve the sensitivity of the instrumentso that instead of giving a full-scale deflectionwith 150 volts, it requires Soo volts, we mustdouble the resistance of the circuit.

Most voltmeters are labelled either with the

No. 77

total resistance or with the resistance per volt,this being a convenient way of expressing therelative sensitivity of different types of volt-meter. In either case it is easily practicable toobtain the actual total resistance of the instru-ment and to add an external series resistanceof such a value that the sensitivity will be of therequired order. Two examples will serve tomake the matter clear :

Example I.-Voltmeter reading 25o volts.Resistance, i,000 ohms per volt. Hence totalresistance =250 x 1,1000=250,000. Meter isrequired to read goo volts for full-scale deflec-tion. Hence resistance must be doubled, that is,extra resistance of 250,000 ohms must be in-serted in series.

Example z.-Meter reads to volts full-scaledeflection and has a resistance of 2,Ooo ohms.What will be the full-scale deflection if 20,000ohms is placed in series?

The total resistance is now 22,000 ohms,which is eleven times the original figure. ThusIto volts will be required to produce full-scaledeflection and the read'ngs on the meter at anypoint on the scale will require to be multipliedby eleven to give the actual voltage across thewhole circuit.

78



Loud -speaker Horns, EffectTHE horn type of loud -speaker can be made

to reproduce faithfully over a wide frequencyband if the rate at which the area increases isdetermined according to an exponential law.Then, provided suitable precautions are takento avoid second resonance effects, a uniformresponse can be obtained from a very highfrequency down to quite a low value.

The lowest frequency which can be repro-duced satisfactorily is determined by what isknown as the cut-off of the horn. In order toradiate sound satisfactorily, it is necessary forthe pressure on the air inside the horn to be inphase with the velocity of the air. That is tosay, the maximum air pressure and the maxi-mum movement of the air must take placetogether.

With the ordinary horn this is the case onlyat the higher frequencies and the two effectsbecome more and more out of phase as thefrequency is reduced, exactly as shown in thediagram. This means that, although the soundis reproduced, it is not radiated to its correctextent and the lower tones suffer.

Using an exponential horn, the pressure andvelocity remain in phase for a considerablylonger period, giving a more or less uniformradiation, until a sudden cut-off point occurs.

Relative efficienciesof exponential hornand cone loud-

speakers

No. 78

of

FREQUEMCY

This cut-off depends entirely upon the designof the horn, and the longer the horn can bemade the lower it occurs. Thus exponentialhorns can be designed at which the cut-offpoint is below 5o cycles per second, and suchhorns will give reproduction comparable with thebest-known methods of reproduction.

In designing an exponential horn, an initialarea should be made only a small fraction of theactual area of the diaphragm of the speakermovement itself. This serves to concentratethe air column on the diaphragm, so that smalldiaphragm movements produce relatively largepressures at the neck of the horn. In this waya distinct increase in the volume of sound isobtained.


Exponential HornsA N exponential horn gives a substantially" uniform radiation over a wide range offrequency. An exponential horn is designed insuch a manner that the area increases at anexponential or logarithmic rate. The law con-necting the area at any point with the distancefrom the commencement of the horn is asfollows :

Log A=.435 Bx+ log A0.Where A 0= initial area.

A= area at distance x from start.x= distance from start.B is a constant the value of which

must be chosen to suit the particular require-ments.

Common logarithms (to base to) are em-ployed.

The larger B is made, the more rapid is theexpansion of the horn, but the higher will thecut-off pcint occur. Thus we can have arather rapidly expanding horn, in which case itwill only be comparatively short. Alternatively,we can have a very slowly expanding horn,which will be very long and which may have tobe designed to coil up in order to obtain areasonably compact arrangement. The latterhorn would be the better from the point of

No. 79

view of reproduction, since it would have avery low cut-off.

The actual cut-off point is determined entirelyby the value of B and the frequency at whichcut-off begins to be serious, that is, at whichpressure and velocity begin to fall out of phase,so that the radiation is not efficient (see SheetNo. 78) is given by the expression :

f=4,000 B.f being the cut-off frequency in cycles per

second.From this data, therefore, it is possible to

design an exponential horn to suit any require-ment: the final area of the horn should beabout 18 in. to a ft. square in order to give ade-quate radiation of sound, although satisfactoryresults can be obtained with somewhat smallerdiameters than this.

In general, the design will be worked out inthe following manner:

i. Decide the value of cut-off required.2. Define B from the expression given.3. Decide the initial area (this is usually

obtainable from the unit employed).4. Work out the area of the horn at increasing

distances, until the final diameter has become ofthe order of i8 in. or 2 ft.


Fig. a. Moving -cal reactioncircuit

mtg.

Fig. b.-Capacity-controlled reactioncircuit

Reaction Control

No. 80

Oirls-TO LE THE detector valve in a receiver carries a mixture ofhigh- and low -frequency currents, and it is essential

to separate the two at this point.It is necessary to provide a ready path of adequately low

impedance for the high -frequency currents, as otherwisethey must, of necessity, force their way through into theL.F. stages.

The simplest way of doing this is to use a high -frequencychoke and condenser filter.

In the case where smooth reaction is employed the reactioncoil should be inserted between the anode and the high -frequency choke, as indicated in Fig. a accompanyingthis sheet. The value of the by-pass condenser shouldbe at least .00i microfarad. It should not be made toolarge, or it may distort the characteristics of the couplingdevice following, causing a loss in high notes, but up to .00 imicrofarad this effect is prevented to a large extent by the

c1.3 presence of the H.F. choke following. For this reasonalone, the H.F. choke should have a high inductanceof at least ioo,000 microhenries.

In the case of capacity -controlled reaction, such as thatshown in Fig. b, the arrangements are similar. Here the twoseparate paths are provided as before, the one for the L.F.through the L.F. coupling device, H.F. being kept out ofthis circuit by means of a high -frequency choke. Thereaction coil should be small, so that a large value ofreaction condenser is required.

79

For the CHUMMY FOUR

THE CHUMMY TOURdescribed in " Wireless Maga-zine," June issue, is a won-derful Set. But to obtain thebest results a really goodLoudspeaker Unit had to beused. That is why the GOOD-MAN P.G3 Unit and Cone Paperwere selected. Don't spoil yourSet by a poor Loudspeaker.The GOODMAN P.G3 Reed Unit isFour pole, Double Acting, Adjust-able, ultra sensitive, yet handleshuge volume, and gives wonder-fully pure and undistorted repro-duction.Your dealer can supply you, or write to us

direct.D.A. UNIT P.G3, Z7/6, includingCone Bush and fixing Screws.

NEW PROCESS CONE PAPER 2 -

OODMAN27 FARRINGOON ST. LONDON . E.C.4

Telephone : City 4472.

The New Wander Plugthat " stays put " in any

H.T. Battery SocketClix-Lox adjustable Wander Plugscut out all risks of shorts. No morecrackling or frying noises when

you use Clix-Lox.Just a turn of the insulator andperfect contact is assured. Afurther turn and the plug is per-manently locked in the socket.

PRICE 2113. EACHObtainable front all Dealers.

LECTRO LINX LTD.254 Vauxhall Bridge Rd., S.W.1

11110110M11


READY RADIO SUPPLY C.°:41 Newcomen Street, London Bridge, S.E.1

Telephone: Hop 6767

THE CONNOISSEUR'S SIX1 Ready Radio Cabinet in polished oak or

mahogany - - ..1 Ebonite Panel 20 in. by 8 in. .. .. 103 Burndept .0005 microfarad variable conden

3 Burndept vernier Wale .. -1 Cyldon Bebe .0002 mierotarad reaction

1 15

2 61 7

81 Lissen 7 -ohm panel rheostat 21 Uremia 400 -ohm panel potentiometer .. 21 Dubilier High -resistance potentiometer .. 62 Bulgin Dial indicators1 London and Provincial on -off push-pull switch 11 Lotus Single -pole change -over push-pull

switch6 Lotus Anti-microphonic valve holders .. 103 Lewcoe 6 -pin coil bases .. .. 82 Peto Scott Baseboard neutralising condensers 101 lgranic Type (4 low -frequency transformer,

approx. 4 tol. 1 102 Dubilier .5 megohm grid leaks with holders.. 71 R. & I. Varley output transformer with

centre -tapped primary 1 1 -1 Wearite double -pole change -over key switch 31 Dubin.- 250,000 ohm wire -wound resistance

with holder - .. 91 Dubtlier 50,000. ohm wire -wound resistance

with holder .. - .. 61 DubWer 2 microfarad fixed condenser .. 31 CDM horizontal high -frequency choke .. 41 Dubilier .006 microfarad fixed condenser .. 31 Dubilier .01 microfarad fixed condenser .. 31 Bulgin Type GES2 flasblamp battery clip ..1 Siemens Type (41 41 -volt grid bias battery.. 11 Terminal strip 216 Belling Lee terminals (ae specified) .. 82 Lectro Linx wander plugs1 yard Rex with spade tag30 feet Glazite 26 Valves (as specified) .. 3 7

117 5

This set can be supplied completely wired and tastefor an additional charge of £6 including Royaltie .

Any of the above parts can be supplied separately.Drilling free. With every Order over Two Pounds, theOfficial Blueprint will be included Free of Charge.Apply for detailed price lists of remaining sets, and all

"Wireless Magazine" cirtuits.THE CHUMMY FOUR

The first published portable to use the screened -gridalve).

Cabinet Completely Fitted, including compassand frame aerial .. . 12 6 0

All other part., in stock.This remarkable set can be supplied ready for use.

Price 818 10 0(Inclusive of Royalties).

We executed the commission for the parte sup -I I plied to Mr. F. I invent in building his "Chummyroy I I

Four," the performanceof which is com-mented upon in this issue.

INLAND : All goods sent POST FREE.CVERSEAS : All orders over £5 Ca liege Paid

EVERYTHING WIRELESS.

The " RADIOLA"

Modernises

yourSet

MOVING

COIL L.S.

and

Batteries

In manysizes

"RADIOLA" de luxe

AStatelyHOME

From

£ 5-5-0

FullyGuaranteed

WINS HIGHEST APPROVAL of Radio Press,Leading Experts, over 3,000 delighted clients.3 ft. high. Rich Solid Oak or Ilahogany-a magnifi-

cent finish-at Load -speaker mat only.

LET US HELP YOU. Suggestions and FULLLIST of exclusive designs FREE. Send now toactual makers

pit i'KETTSCABINETS

M.G. WORKS BEXLEYHEATH : KENT

UsefulAccumulatorConnector

TLLUSTRATED below is a new1 Clix product that will appeal toeverybody who has an accumulator.It takes the form of a robust terminal" top " provided with a hole intowhich a plug can be inserted.

This device, as can be seen, is par-ticularly neat and has many advan-tages in use.

It is made by Lectro Linx, Ltd., of254 Vauxhall Bridge Road, S.W.I.

The Gramo-Radio Four'THOSE who are thinking of build-

ing one of these sets, described onpage 337 of the May issue of the WIRE-LESS MAGAZINE, should note that aprinter's error occurs in the list ofcomponents reproduced on page 340.

The jack should be an IgranicNo. 68 or No. 65 and not a No. 63.Wiring up is easiest when a No. 68jack is used, although a No. 65 issuitable.

EPOCHMOVING COIL PARTS

are guaranteedto be the

Finest inCONSTRUCTION.

Finest inPERFORMANCE.

Finest in FINISH.Price only

3 :10 : 0complete.

Try one on approval for 10 days and convince yourself.From all dealers and from stock from

EPOCH ELECTRICAL SOCIETY LTD.,53 Gracechurch St., London, E.C.3. Phone: Royal 8570.

(Full Par/imams on application).

80

SIGNAL LAMP ANDPANEL ILLUMINATOR

Price 3/. each

AND SO TO BED-Leaving the wireless ontU night By the timeyou discover the tact, theMe of your valves will

\ have been shortened bymany valuable hours, andboth H.T. and L.T. bat-teries will have beenwasting their sweetnesson the desert ether.Fit one of these Haightruby pilot lamps whosebrilliant glow is a positivesafeguard against suchcalamities.Special low consumptionbulbs taking only atraction of an ampere canbe supplied by us for theselamps. Suitable for 2, 4 or6 volt accumulatorseach.

-.Waw&V.VA,1.f9

RADIO NIANCIRACTURERS,E- 9.10.11. CURSITOR ST CHANCERY LANE. E.C.9.i Ph o oc ton iv 207 2 (

A.A.AAAAAAAAA. A AAAAAA AAAAAN

A Index to AdvertisersAshley Wireless Telephone

2Baker's Selhurst Radio ... 72Bedford Electrical and

Radio Co., Ltd....Belling & Lee, Ltd. ...Bernard Jones Publications,

Ltd. ... ... Cover iiiBird, S. S., & Sons, Ltd....British Ebonite Co., Ltd....Bulgin, A. F., & Co.Burndept Wireless, Ltd. ...Carrington Mfg. Co., Ltd....Celestion Radio Co.Clarke, H., & Co. (Man-

chester), Ltd. ...Cossor, A. C., Ltd.... ... 65Dubilier Condenser Co., Ltd. 67Fastick, J. J., & Sons, Ltd. 74Epoch Electrical Society, Ltd. 8oEver Ready Co., Ltd. Cover iiFerranti, Ltd. ...Fluxite, Ltd.Formo Co. ... 72Garnett, Whiteley & Co., Ltd. 75Goodmans, Ltd. ...Graham Farish Mfg. Co. ...Igranic Electric Co., Ltd....Lectro Linx, Ltd. ...Lissen, Ltd.London Electric Wire Co.

and Smiths, Ltd. 67Lyons, Claude, Ltd.Mic Wireless Co. ... 78Mullard Wireless Service

Co., Ltd. ... ... Cover iv788o72738o

71

77

Omnora, Ltd. ...Pickett Bros. ...Potter, H. B., Ltd.Raymond, K. ...Ready Radio Supply Co....Ripaults, Ltd. ...Sifam Electrical Instrument

Vandervell, C. A., & Co., Ltd.Whiteley, Boneham and

Co., Ltd.... ...Wilson, H. L. ...Wingrove & Rogers, Ltd....Wright & Weaire, Ltd. ...

713

8o697176

3

79776879

4

74

68

747o

71

783

69

IITYVYTTYVVVVYYTYVVYYTTYV

I Wireless Magazine, August. 192811'AMATEUR SET -CONSTRUCTOR'S

FULL-SIZE BLUEPRINTSFull-size blueprints are available of the following sets. Copies of the "WirelessMagazine " and of "Amateur Wireless " containing descriptions of all these sets can

be obtained at 1s. 3d. and 4d. respectively post free.

CRYSTAL SETSAll these 6d. each, post free.

For the R.C. Enthusiast . WM13Fonotrol Set .. WM14Hi -lo Set .. WMI8Two -programme Set .. WM25Half-hour Set .. WM28Centre -tap Set .. . . WM5oAlternative -programme Set .. AW 39Super Set AW 64Tapped -coil Set : : AW o5" Best -yet " Set .. AW1 14

ONE -VALVE SETSAll these is. each, post free.

One-valver for a Frame Aerial .. WM47Long-range Hartley .. WM54Reflexed One for the Loud -speaker WM66All -wave Reinartz . AW zHartley D.X. AW 27Reinartz Plug-in One .. AW 46Constant -coupled ......AW 65Economy One .. AW 71Loud -speaker Special ......AW 78Ultra -sensitive Hartley One AW t"3Fan's Short-wave One .. .. . AVVI19

TWO -VALVE SETSAlt these Is. each, post free.

Loftin -White z (D, Trans) Price is. 3d.,with copy of "W .M " . . . . WMzo

One -dial 2 (D, Trans) .. WM23Girdle Two (D. Trans) Price ts. 3d.,

with copy of "W.M." WM3oMains -fed 2 (D, LF) . .. WM37British Broadcast 2 (D, Trans) .. WM44Two -programme 2 (3, Trans) .. .. WM56Q -coil 2 (D, 'Trans) .. .. WM62Crusader (D, Trans) .. .. WM69Flat -dweller's 2 (HF, D) WM76KLi 2-valver (D, Trans)One -control 2 (D, Trans) :: : : AW 6Wide -world Short-wave (D, Trans) .. AWReinartz z (D, Trans) .. AW 21Empire Short-wave AW 28Next Step 2 (D, Trans) .. AW 34Centre-tap z (D, Trans).. AW 42Three -option 2 (D, Trans) .. AW 51Rover z (HF, 13) . AW 53General-purpose 2 (3, Trans) .. AW 55All -wave (D, Choke) .. AW 57Yule (D, Trans) .. A W5930/- 2 (D, Trans) AW 61Economical 2 (D, RC) .. AW 66Britain's Favourite (D, Trans) Price 7d.,

with copy of "A. W."AWHome-and-Abro td (ID, Trans) AW 7774

Two -wave (D, Trans) .. : AW 83Ultra -selective Hartley (ID, Tram) AW goOceanic Short-wave (D, Trans) . AW 91Trapped Reinartz (ID, Trans) .. . AW 92"Q" 2 (D, Trans) w- 99Long Distance Two (HF, D,) . AWiro

THREE -VALVE SETSAll these Is. each post free.

Continental (HF, D, RC) .. .. WM 7Wave -catcher (HF, D, Trans) .. WM t9

A blueprint of any one set describedin the current issue of the "WirelessMagazine" can be obtained for half-price up to the date indicated on thecoupon (which is always to be foundon page iii of the cover) if this is sentwhen application is made. Theseblueprints are marked with an asterisk(*) in the above list and are printed inbold type. An extension of time will bemade in the case of overseas readers.

Screened -grid (HF, D, RC) .. WM2tFive -guinea 3 (HF, 13, Trans) .. WM29Mains Three-valver (ID, 2LF) .. WM34Dominions Short -waver (D, z Trans) .. WM39'Tuned -anode from the Mains (HF, D, LF) WM43Screened -grid Short -waver (HF, 13, 'Trans) WM5 tMetropolitan (D, 2 LF) WM48Everyday (ID, 2 Trans) .. .. . WM52Music Charmer (D, RC, Trans) WM6oBritannia (D, RC, Trans) .. WM67Home and Garden 3 (D, 2 RC) .. W NI78*Glee -singer Three (D, 2 RC) WM92M.C.3 Star (HF, D, Trans) .. AW 16Split -primary (HF, D, Trans) .. AW 24Lighthouse 3 (D, 2 Trans) .. AW 29Modern Tuned -anode (HF, D, Trans) AW 35Tetrode 3 (HF, D, Trans) .. AW 36Alternative -programme 3 (D, 2 Trans) .. AW 38All -from -the -Mains (D, 2LF) AW 41Special (D, 2LF) AW 44Economy 3 (D, 211C) AW 48Short-wave (D, RC, Trans) .. AW 5oEther -searcher (ID, RC, Trans) AW 52Standard (D, 2 Trans) .. AW 56Hartley D.X. (D, RC, Trans) .. AW 63Britain's Favourite (ID, RC, Trans) Price

7d., with copy of "A.W." AW 72Broadcast 3 (D, RC, Trans) .. AW 76Selectus 3 (HF, D, Trans \ AW 81Q -coil 3 (D, RC, Trans) AW 84Clarion 3 (D, 2 Trans) .. AW 88Miniature Hartley Three AVViorSummer -time DX Three (HF, D, Trans) AWro6Three -valve Mains Receiver (HF, ID, Trans)

AWro9

FOUR -VALVE SETSAll these is. 6d. each, post free.

Revelation (HF, ID, RC, Tram) WM24Simplicity (HF, D, 2 Trans) .. WM49Astral (AF, D, 2 RC) .. .. WM53'I'rapped 3-4 (D, 212C Paralleled) .. WM6iStation -finder (HF, D, 2RC) WM68Gramo-Radio 4 (D, RC, z Trans Push-

pull) .. WM7oQ -coil 4 (HF, D, Trans, RC) .. WM71Screened grid 4 (HF D, 2RC,) .. WM77All-from-the-MainsFour (HF, 13, LF) WM86*Five -pounder Four (HF, D, RC,

Trans) . WM91All-purpose 4 (HF, 1D, RC, Trans) .. AW 43'Tuned -anode 3-4 (HF, D, 2 Trans) .. AW 49C.T.4 (HF, 1D, RC, Trans) .. AW 58Special 4 (HF, 13, 2LF) AW 7oI.H.C. 4 (2HF, D, Trans) .. AW 87"Q" 4 (HF, D, RC) .. - AW 98Near and Far Three -Four (HF, D, RC,

Trans) .. AWI 13Pick-up Three-four (D, z Dual -imp.) AW118Explorer Four (HF, D, RC, Trans) .. AVV12o

FIVE -VALVE SETSAd these is. 6d. each, post free.

1927 Five (2HF, D, z Trans) .. .. WM 6Two-volter's 2 (Trans -Parallel Power) .. WM11Exhibition 5 (2HF, D, RC, Trans) .. WM33Phoenix (2HF, D, 2LF) .. WM421928 Five (2HF, D, 2 Trans) .. WM46All -the -world 5 (2HF, 1D, 2RC) .. WM63Cataract 5 (HF, D, RC, Push-pull) .. WM79Individual 5 (zHF, ID, 2 Trans) AW 25School 5 (HF, D, 2RC) .. AW 85

SIX -VALVE SETSIs. 6d. each, poit free.

Nomad (2HF, D, RC, Push -Pull Trans) WM3r*Connoisseur's Six (2HF, D, RC,

Push-pull) WM88Short-wave Super -6 (Super -het, Trans) AW 67Adaptor for above (see miscellaneous list) AW67a

SEVEN -VALVE SETSls. 6d. post free.

Simpladyne (Super -het) WM22

PORTABLE SETS PriceFoal Free

Springtime 2 (D, 'Trans) .. WM12 1/ -Countryside 4 (HF, D, 2 Trans) .. WMx7 x/6Handy 3 (D, 2 'Trans) .. WM27 1/ -Sunshine 5 (2HF, 13, 2 Trans) .. WM74 i/6Chummy 4 (HF, 13, RC, Trans) .. WM8o x/6Chummy 4 (with modification for

LS and HT).. WM8oa x/6Sidecar Portable (2 HF, D, RC,

Trans) .. WM83 x/6*Pilgrim Portable (D, Trans).. WM94 r/6Motorists 4 (HF, D, 2 Trans) AW 14 1/6M.C. 3 (HF, D, Trans) .. AW 22 1/-Holiday 3 (D, 2 Trans) _ AW 32 1/ -Easter 7 (Super -het, RC, Trans).. AW 89 1/6Table Grand 4 (HF, ID, 2RC) AW 93 1/6Attache Portable 2 (HF, ID) AW 96 1/ -Companion 5 (2HF, ID, RC, Trans) AW too 1/6Daventry Portable (13, Trans) .. AW 105 x/-Daventry Loud -speaker Portable

(zHF, D. RC, Trans) .. AW to7 x/6Town and Country (HF, D, RC,

Trans) AW x i t 1/6House and Garden (screened -grid

HF, D, RC, Trans) .. AW 116 x/6AMPLIFIERS

All these ls. each, post freeTwo -valve D.C. Mains Amplifier WMi6Range Extender (HF Unit) .. WM38True -tone Amplifier (3 valves) . WM47Gramo-radio Amplifier (2 v.) .. WM72One -valve D.X. Unit .. .. AW 37Utility (RC, Trans) .. .. AW 68Screened -grid HF Unit .. .. AW 75One -valve LF Unit .. .. AW 79Add-on HF Unit .. .. . AW 8zSuper -power Push-pull .. .. AW 86Hook on Short -waver ., .. AWro4Purity Amplifier.. .. AW robAdd-on Distance -getter _ .. .. AWi 17Two -valve L.F. Amplifier (RC, Trans) AWI21

MISCELLANEOUS Price,

Po"Volume -control Unit .. WM4oFree

A.C. Mains Eliminator .. WM4t r/ -Cone Loud -speaker WM55 1/-A.C. Adapter for "Simpler Wire-

less" Sets WM57 1/ -Moving -coil Loud -speaker .. WM58 1/-D.C. Mains Eliminator .. WM59 1 /-Wavetrap . WM64. 1/ -Valve Tester and Paralleling Unit WM65 r/ -Portable Cone Loud -speaker .. WM73 1/ -Permanent -magnet Moving -coil

Loud -speaker .. _ WM75 IF"Junior" Moving -coil Loud -speaker WM8r x/ -Universal Short-wave Adaptor .. WM82. 1/ -Heterodyne Wavemeter AW 7 1/ -Rectifying Unit for " Simpler Wire-

less" Sets AW 62 1/ -Adaptor for Short-wave Super Six AW 67a -/6H.T. from A.C. Mains .. AW 73 x/-"AW" Moving -coil Loud -speaker AW 97 xi-H.T. Eliminator for A.C. (zoo v.

output) .. AWroa z/ -Moving -coil Output Unit AW 115 r/ -

Send, preferably, a postal order(stamps over sixpence in value

unacceptable) to

WirelessMagazine

Blueprint Dept., 58,161Fetter Lane - E.C.40t

Half- BLUEPRINTpriceCoupon Valid untilAugust 31, 1928

FOR ANY ONE SET CONSTRUCTIONALLY DESCRIBED IN THIS ISSUE.

-----------Felez!ir INFORMATION Coupon Valid until

August 31, 1928NOT MORE THAN TWO QUESTIONS TO BE astrEo AT A TIME


Putting it briefly, my success is un-doubtedly due to the introduction of theMullard P.M. Filament Radio Valvesinto my receiver.

Since the first Mullard P.M. Valvecame out many different types havebeen designed to meet the demands ofmodern radio receivers to the fullestmeasure of efficiency and at the sametime satisfy the needs of the morediscriminating user, but the fundamentalbasis of each and every type of MullardP.M. Valve remains the same potentialfeature-the wonderful Mullard P.M.Filament !

I appreciated this endeavour on thepart of its manufacturers to bring mebetter radio. The outstanding features

about this wonderful Filament were putclearly before me, in terms I couldunderstand - greater length, greaterthickness, huge emission, immensetoughness and mechanical strength, andfrom the first moment I tried a MullardP.M. Valve the improvement in recep-tion was apparent.

The publication of the National PhysicalLaboratory test report on Mullard P.M.Valves proved conclusively their realvalue, and gave every radio user, whohad hitherto been groping in the dark,a light and a sound lead.

Every radio dealer sells Mullard P.M.Radio Valves, and it will pay you toask about any new Mullard productswhenever you're in a radio shop.

MullardTHE MASTER. VALVE

Printed in England: Published by BERNARD JONES PUBLICATIONS, LTD., 58/61 Fetter Lane, London, E.C.4.Sole Agents for Africa: CENTRAL NEWS AGENCY LIMITED. Sole Agents for ALLUEIRSia GORDON & GOT CH LIMITED. August, 1928

4 a four for wireless a azme

Documents