popular wireless, april 21st, 1928. this year's "chitos two" re=ge)registered at the...

POPULAR WIRELESS, April 21st, 1928. REGISTERED AT THE G.P.O. AS A. NEWSPAPER.

THIS YEAR'S "CHITOS TWO" re=ge)

No. 307. Vol. RM.

ula.r 3d....I.'very Thursday

PRICE

irelessINCORPORATINGVIRELESS" April 21st, 1928.

SPECLIL FEATURES IN THIS ISSUE1Vnertooirxr4G YOUR FtlEsur..rs. ELYCCEIBECF`IYI, SOLDERING

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One of the most interesting of modem radio developments is the " Beam," whereby long-distance wireless communication con be clrrielcut on low power and directionally. Our cover photo shows Mr. T. L. Eckersley and the apparatus he used in a recent demonstration uni

letture of this system.

ii POPULAR WIRELESS April 21d,

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How delightful to be always cer-tain of your station-to be ableto tune in whatever station youdesire with no time wasted inundecided searching.

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WHAT YOU GET FOR YOUR MONEY.s. VANES of stout Dress sheet. 2. SPACERS, between which vanesare firmly clamped, ensuring rigidity and eliminating possible resistancethrough loose connections. Consistent spacing assured by the extremeaccuracy to which spacers .are turned. 3. TERMINALS-one givingdirect connection with the frame and rotary vxnes and the other with the fixedvanes. 4. INSULATORS of high quality moulding material under com-pression, forming an effective insulation of the stator plates, and eliminatingdielectric losses. 5. END PLATES of the skeleton type, ensuring rigidityand lightness. C.. KNOB AND DIAL of finest finish and engraved in moosingle. degrees. Diameter 4 ins. Main knob rotates moving vanes direct.7. SMALL KNOB. This moves independently of the main knob andworks a slow-motion drive. 8. SLOW-MOTION BALL DRIVE. Approx.redwtion ratio of 2C0-1 enabling precise tuning adjustments to be easilysecured. 9. BALL RACE, giving a velvet -smooth movement whether thedirect or slow-motion drive is used, and with entire a',sence of backlash ineither case. One Hole Firing -1 in. clearance. A large nut is providedfee mounting on panel. Maximum Capacity '0005.

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©In

Popular Wireless, April 21st, IP. 277

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278Popular Wireless, April 21st, 1928.

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2463

Popular Wireless, April 21st, 1928. 279

PopularWirelessScientific Adviser :

Sir OLIVER LODGE, F.R.S.Editor :

NORMAN EDWARDS.Technical Editor: G. V. DOWDING, Grad.I.E.F..

Assistant Technical Editors: K. D. ROGERS, P. R. BIRD,G. P. KENDALL, B.Sc:, A. JOHNSON RIANDALL.

RADIO NOTES AND NEWS.The Event of the Year-Teashop Tattle-London's Largest Musical Library

Another Radio Mystery-A World Beater-The Amateur's Paradise-Radio Scepticism.

The Event of the Year.1T is announced that the National Radio1 Exhibition, organised by the Radio

Manufacturers' Association, will beheld this year at Olympia (New Hall),September 22nd to 29th inclusive. Fivemonths' notice is given to enable anygenuine " fans " who may have intendedmarrying that week to alter their arrange-ments.

" Mike " Cult Spreads.THE Government of Colombia (South

America) has ordered a broadcastingstation for Bogota, the capital, and

the presumption is that the service will beoperated by the Government-at a deadloss, I should say. Colombia is a hot -bedof " atmospherics " most of the year, andis covered with mountains ; hence recep-tion will present some pretty problems, anda " regional scheme " would make CaptainEckersley think on all gears at once. ,

If-TF-a big if-the Post Office line1tele-graphs and radio services are handed

over to private enterprise, will the PostOffice stick to the very profitable job ofCollecting our licence fees, or will this be-come the prerogative of the combine ? Andif private enterprise takes it over will therebe more prosecutions or more " pirates " ?Finally, will the Post Office still be thelicensing authority and if so, why ? Whyshould it have the last word on the subjectif it has had to give up its services ? Thesequestions are hypothetical but fascinating.

Hint to Aberdonians.MAN! I mind the nicht, a few weeks sync,

when something foozled my set bangin the middle of an orchestral piece

for which I have a weakness. What did Idae ? Stifling the appropriate adjectives, Isprang to the mantelshelf and seized athin, trumpet -shaped glass vase. I hap-pened to know that the man next door kepthis set against the party wall, so, clappingthe base of the vase flat against the wall Iapplied my ear to the open end-and heardthe piece through, losing not more than adozen bars. Surprising, but true.

Teashop Tattle.MY modest club having been rendered

uninhabitable by spring -cleaners Itook my morning, meditative coffee

last week in the smoking -room of a tea-shop, one branch of a firm of caterers whosternly forbid one to tip the " nippy." Buthow changed things were ! Instead of theclash of dominoes I heard the steady hum ofthe radio fan. It occurred to me that theback cover of that very sporting tariff oughtto be left blank for the pencil of the diagramdraughtsman, a piece of eraser beingfastened to the sugar -tongs. A small blaclf-board, too, would prove popular. Andwhy are there no loud speakers in lieuof the piano -fiddle -'cello band of the morepretentious branches ?

Music Note.AS we are favoured with much jazz by

radio it may not be out of place toreveal the origin of the saxophone.

According to the B.B.C. the thing was

invented in 1840 by Adolphe Sax, whuspecialised in making wind instruments forFrench military bands.

Selected Numbers.APRIL 20th : Last National Concert

of season ; Queen's Hall ; Sir H.Wood.. April 19th and 21st : concerts

ity the newly -formed National Orchestraof Wales. April -21st : Murton' CollieryPrize Band from Newcastle. April 23rd :St. George's Day. Performance of " HenryV " ; also Lord. Birkenhead's speech at theAnnual Banquet of the Royal Society ofSt. George, relayed to 5 G B.

London's Largest Musical Library ?IWONDER. Anyhow, the B.B.C. Music

1 Librarian at Savoy Hill claims that hehas of orchestral pieces alone no less

than upwards of 8,000, some of them havinga hundred different parts. In addition,he keeps six or seven thousand vocal scores,

(Continued on next page.)

WAIT -AND SEE?

This optimistic home -constructor tackled the task of assembling " television " parts, but judging byhis expression appears to have struck a snag.

280 Popular Wireless, April 21st, 1928.

NOTES AND NEWS.(Continued from previous page.)

and several hundreds of military bandparts. As an interesting sidelight, itappears that dance music is not so carefullyclassified as the rest, because it lives onlyfor about six weeks. " Chamber Squeals 'evidently rank higher than dance music.But that is probably due to the carelessnessof some office boy.

Another Radio Mystery.COPENHAGEN reports that an iron -

handled coal shovel hanging from ahook, attached to a water -pipe at

Kalmar Fire Station, Sweden, has takento acting as a loud speaker ; perfect enuncia-tion and intonation. Experts are rushingto the spot in the hope of (a) proving theshovel to be a spade, and (b) getting anovel idea for the autumn exhibitions.

The Opportunist.IREAD in the newspapers that last

1 month Judge Sturgess, in the courseof a case involving a dispute about

some wireless sets, remarked that therewas not, much doing, so they might aswell hear the wireless ; which they did.Not the first time that the " lyre " hasoccupied the attention of a court of law.One is bound to admire the judge's " nerve,"though whether the audition was inkeeping with the dignity of a court isanother matter.

A World Beater.IN each one of the 7,700 guest -rooms of

the Staler hotels in six U.S.A. citiesthere are arrangements for radio recep-

tion, with a choice of two programmes.Guests can have radio at any time withoutrequest or ,charge. In addition to the twoprogrammes, which are looked after byskilled operators in the control -room, thehotel orchestra is sometimes " laid on," aswell as important speeches during banquets.In the larger rooms there are loud speakers ;in the others the 'phones are placed in adrawer of a table near the head of the bed.

Cure for Oscillation.ABATH victim of oscillation recom-

mends that the owner of a set whichoffends by oscillating should dis-

regard the B.B.C. pamphlet, attach his" earth " wire to the positive H.T. terminaland connect his aerial to the " earth "terminal of his set. Not bad-but toolenient. I recommend that the A and Ewires be connected together, that thepas. and neg. of the H.T. be connected toL.T. pos. and neg. of the set, and that themains be connected to H.T. pos. and neg.This is a " money back " cure.

A Real Test.AN expedition under the leadership of

Major Court Treatt is now on itsway to a little-known part of the

Sudan and it is taking with it a transmitterspecially designed by Marconrs for com-munication with England. It is a one -valve transmitter using about 20 watts onthe anode, said watts being delivered by ahand -generator. The wave -length will beabout 30 metres and a half -wave -lengthaerial 15 metres long is to be used. DXhounds will now place their noses downand their tails up, for this is a scent worthy

of their skill. Who will be the first to" give tongue " ?

Hunt the Caravan.HERE'S an interesting search for short-

wave enthusiasts who know how tocomb the ether. A Chevrolet cara-

van left Cape Town on March 7th, en routeto Stockholm. It has with it a transmitterworked by a generator driven off a belt fromthe car. Transmissions are made every day(elephants, etc., permitting) on 20 and 40metres, with the call -signal A 8 M. Thesetransmissions take place most days atmidnight and 4.0 a.m. G.M.T. Now then !If you suffer from insomnia, here's some-thing to pass the time.

Humble Suggestions.IF we must have " talks," and, of course

we must, I suggest that the B.B.C.should attempt to introduce more

" human touch " and to eliminate moreof the academic, text -book, element ;

Nifiiiiiiimmiiiminimmimmillummimimmummiiim

-.1E One man is said to have written over five Ehundred letters to the B.B.C. Hl wireless= licence should be endorsed for exceeding the H.g screed limit.-" Humorist." a-

=..:1 TO -DAY'S FABLE. -.-7-2

H During the emission of a Quiet Talk on HE Marine Algae and British Rock -Pools from HH 2 L 0 the other evening, Professor Google =

suddenly went mad and began to scream and Htell smoking -room stories. E= Listeners -in, on reading of the sad affair

next day-(etc.).-" Daily Mail." --.-,

The mystery of the man who wrote to the ..E.:

H. B.B.C. and signed himself "Satisfied Lis-tenet has now been explained. The B.B.C. E

E apparently failed to discover the " Dis." =.= PRACTICE MAKES PERFECT.= First Hubby : " Is your wife getting much "2E help from the daily cooking hour on the g.= radio P "E 'Second Hubby : " Oh, in a way. To -day EH she got three new recipes while she let the =

pie burn." -= *

SHORT WAVES.

* ..-H-.

g " Wireless in Warfare.

Distant ControlH of Death -dealing Machines" runs a headline HE: in the " Manchester Evening Chronicle."

The eight -valve super -het next door would E14, be quite a useful item to hurl at the enemy. F.

Never refuse your neighbour the loan of a*

E valve-that is, of course, providing you have =H several duds on hand. =

a a E.A FILAMENT ELIMINATOR.E There was a young radio student _

=a Who was told to be careful, but wouldn't ;g, On " A plus " he placed

B.90 ' in haste- E.Then he tried to tune in, and he couldn't!- =

1-4" Radio. News."

(In America the H.T. is called the " B " E and L.T. the " A " supply.)

"

==FTi111111110110111111111111111111111101111111111111111111111I1111111111110

that it should try to " make contact "with listeners. For instance, I believethat a series of talks about health, by somedoctor who is not a crank, would bewelcomed. Here are a few titles : " Howto conserve health at twenty, forty, andsixty " ; " The truth about tobacco andalcohol " ; " How the mind affects thebody " ; " A healthy body-what is it ? "

Talks Without Tears.

YOUwill notice that I have excluded

vitamins and phagocytes. Then,what about " Careers for bays and

girls "-a mighty problem for most parentsin these days. Again, " How to travelabroad " ;_ heaps of people miss foreigntravel for lack of plain information aboutwhere to go and how much it costs. They

stew in some crowded seaside place andspend almost as much as would pay for atrip to Spain or Switzerland. Finally-but only because space is limited-whynot some more talks by workers ? We all-like to know about the next man and hisjob. Common people are closer to us thanthings, theses, and theories.

A Little Learning-is. . a dangerous thing, bu of

nearly so funny as none at all. Talk' of" talks," which, under the present broad-casting regime, give us a smattering of lotsof things, I read a good joke about a manwho told a friend that at a dinner the nightbefore, his hostess had asked him whetherhe liked Botticelli, and that he had repliedthat he preferred Chianti. " You ass ! "said his friend, " Botticelli isn't a musician,it's a kind of cheese."

The Amateur's Paradise.Y notes from time to time on this subject

1T-1- bring in a steady trickle of letterswhich already begins to show that

South Africa has been specially favoured.This is not surprising, as old radio handswill agree when they recall the extraordinarydistances over which ships were able tocommunicate with that part of the world.But all is not well with South Africanbroadcasting, and I shall revert to thesubject shortly. I thank C. R. S. (S.Africa) for his letter and invite him to makeup the " Sydney " Two and give me newsof it,

They Say-What Do They Say?LET them say. Firstly, Mr. D. C. Thomson,

Northern Area Director of the B.B.C.,says that the B.B.C. considers that it

is impossible for efficient use to be made ofbroadcast lessons without the co-operationof the teacher in the class -room. Oh, foun-tain of exhaustless wisdom ! Next : Ro-tarian G. Pochin, referring to music byradio says, " Mechanical music has nowbecome a menace." He added that musicvia radio is lacking in soul and inspiration.By dint of superhuman restraint I refrainfrom comment.

On the Right Track.THE most sensibleremark on programme

building I have ever heard from abroadcasting authority comes from

3 L 0 (Melbourne). " It is only by a com-prehensive study of average tastes and bypsychological research that the broadcastingcompanies can gauge the requirements oflisteners." The italics are mine. I recom-mend the B.B.C. to study that sentence, andbeg them to accept the doctrine it contains.

Radio- Scepticism.MR. ELSTON certainly has " started

something "-correspondence beinga part of it. As our letter columns

show, he has some sympathisers, but not afew antagonists. Mr. Rowett's letter,published in our issue of March 31st, hitsone nail on the head when he suggests thatskill in manipulation counts for a lot. Iwould suggest that some of the radioclubs should devote an evening to thismatter and report to me what broadcastingstations they receive, to the satisfaction ofall present, on a loud speakeroising a three -valve non -reflex receiver, Please mentiontype of receiver,

ARIEL.


THE importance of havingan aerial of thick orstranded wire is gener-

ally realised, but it must beremembered that it is just asnecessary-in fact, more so-to use low -loss wire for down -leads and earth wires.

Thadact is often over-looked' that the earth leadhas as much effect on thetuning of a set as has theaerial itself, for it forms partof the aerial circuit, and itsometimes does not matter agreat deal which terminal onthe set is marked " aerial,"and which " earth."

With regard to the earthconnection, it is too oftenassumed that any water pipe is a goodearth, and earth leads are sometimes foundsecured to waste pipes which never evenenter the ground. if a water pipe is to beused, the main cold water supply pipeshould always be selected.

Poor results are often obtained becauseof mistakes incorporated in the aerialtuning circuit of the receiver.

A tuning circuit employing a small coiland a large variable condenser which willcover a very wide wave -length range is notefficient. in fact, the smaller a paralleltuning condenser, the better.

Tips on Tuning.In the case of a two -circuit tuner, tighten-

ing the coupling between the coils does notnecessarily increase signal strength, *as isoften supposed. If the coils are near enoughto transfer a large amount of energy fromprimary to secondary, they are also nearenough. to transfer energy back to theaerial from the grid circuit, and damp outsignal strength by radiation.

It is sometimes imagined that verycritical tuning is ideal for selective reception.This is not the ease, as critical tuning maysimply depend upon the wave -length rangecovered per degree of the tuning condenserdial, and is not the same thing as sharp, orselective tuning whichdepends upon thenarrowness of thewave - length bandover which any sta-tion is heard.

Apartf romthe tun-i n g arrangements,there are few mistak-en ideas that can beentertained with re-

, gard to a simplecrystal set, exceptperhaps the veryserious and illogicalerror of supposingthat " because it isonly -a crystal set,any old hook-up willdo." On the contrarya crystal set mustmake the best possi-ble use of what itcan derive from theether, as it cannotrelease energy froma high-tension bat-tery. We may takeliberties with theefficienpy of a valveset, tut every detail

IMPROVINGYOUR

RESULTS

*1

.Some simple expediencies which +

make for better radio reception.By C. E. FIELD, B.Sc.

* 41..0- 00-0-0-4..10-11-41.---------- *

should receive consideration in a crystalreceiver.

Valves, perhaps, come in for more mis-understanding than any other wirelesscomponent, probably because of the rapidadvances that have recently been made intheir design and manufacture.

For instance, because a valve is labelled" General Purpose " it does not followthat it is the most suitable valve to employin any position. Rather should a general-purpose valve be regarded as " Jack of alltrades and master of none."

That Unwanted Impedance.In the case of specialised valves, the

significance of the valve impedance is oftenmisconstrued. This is probably because,for high -frequency or resistance -coupledcircuits a high-iinpedance " valve isusually recommended, whereas it is a" high -amplification " valve which isreally required. High impedance is anecessary evil, which is inseparable from

high amplification,. and manu-facturers strive to producevalves with the ratio of am-plification to impedance f i.e.conductance) as high aspossible.

Except from considerationsof economy of high-tensioncurrent (but not high-tensionvoltage), high impedance isof itself no advantage.

Disappointment is some-times expressed by experi-menters who, replace a smallpower valve by one of thesuper -power class, and findno increase in volume. Thisis as it should be, for theamplification factor of asuper -power valve 'is con-

siderably lower than that of a smaller valve.If a large power input is being dealtwith, however, the larger valve will givea very definite improvement in tonalquality. Nevertheless, it must not beforgotten that it will not even do thisunless it is given an increased grid bias.A super -power valve with 4, volts on thegrid is no better than a general-purposevalve similarly biased, but consumes some-where about 10 times as much high-tensioncurrent.

H.T. and Grid Bias.The importance of high-tension voltage

is not generally appreciated, and it is quiteusual to find amateurs reluctant to employmore than about 100 volts in low -frequencyamplifiers, for fear of increasing 'volume atthe expense of quality. This is mostunlikely, and in order to obtain the bestresults from an amplifier the high-tensionshould be twenty or thirty volts in excess ofthe maximum value recommended by thevalve manufacturers, to compensate forloss of voltage in transformer or speakerwindings.

In connection with the biasing of valves,it is evident from correspondence columnsthat many are under the impression that a'high -resistance grid leak tends to prevent

the grid voltage fromreaching the arid of

The new wireless station at Croydon.This is the roof of the transmitterbuilding. The four copper tubes inthe middle are connected to the mainearth, which is buried around. Thereare also four lead-in insulators, threeof which are shown in the photothrough which the aerials are led in

to the transmitters. (Marconi Co.)

the valve. This isnot so, for so long asno grid current isflowing (as occurswhen a valve is over-run) there is novoltage lost in thegrid leak.

A further pointregarding grid biaswhich is very wellworth bearing inmind is that someH.T. batteries,notably the Lissen,have special 14 -volttappings at theirminus ends, so thatthey can supply gridbias as well as H.T.

The effective H.T.minus in such a casecan be, for instance,the 9 -volt tapping.This will also repre-sent grid -bias plus.The lower tappingscan then be used asbias negatives.

282

21,000 TELEVISHEION CHALLENGE. It

Mr. Baird Fails to Accept.By THE EDITOR.

WE have to announce this week theformal withdrawal of our E1,000Television offer to Mr. Baird and to

the Baird Television Development Co.We will not reiterate the terms of that

challenge, nor the reasons which inspired it.Our readets are familiar with both, notonly through the columns in this journal,

Mr. John Logic Baird.

but also through the columns of the dailyPress. We are sorry that Mr. Baird and hiscompany did not accept our challenge andthus, for the first time, demonstrate beforean impartial -investigatory committee, com-posed of scientists of repute, the realpossibilities of the Baird Television system ;and we are all the more sorry because theacceptance of the challenge, and theensuing demonstration would have com-pletely cleared up the misapprehensionsexisting in the public mind with regard totelevision generally.

"Excessively Optimistic Beliefs."However, the effect of Mr. Baird's re-

fusal to accept our challenge has, at anyrate, done a great deal to dispel manyexcessively optimistic beliefs held in con-nection with television, and we are glad toreport, from reliable information suppliedto us from various sources, that our relationof the exact position of television to -day,and the views of eminent scientists we havepublished, have had the effect of warningmany enthusiastic but over -credulous peoplewho intended spending a good deal ofmoney on home television outfits, com-ponent parts, etc., in the belief that theywould have television in the home.

Although, from the large correspondencereceived from our readers, we are convincedthat our policy with regard to television,and in particular to the Baird Co., has beencorrect, and in the best interests of ourreaders, we have received one or two lettersfrom readers reproaching us for attemptingu " crab " television experiments.

We always welcome criticisms, but

criticisms of this nature are not veryvaluable, inasmuch as they show anignorance of the views we have expressededitorially, the views expressed by SirOliver Lodge, Dr. Roberts, and otherscientists, and the terms and conditionsof the offer made to Mr. Baird.

Mr. Baird has been reported in the Pressas giving at least three separate anddifferent reasons for not accepting ourchallenge-all more or less contradictory-and in the second issue of a paper devotedto the subject of television we find thefollowing editorial comment :

" We note that -one of our wireless contemporariesis now endeavouring to put before its readers the realfacts about television. The only comment which wewould make,. -in passing, is that whilst the journal inquestion was endeavouring to cast ridicule on Mr.Baird's proposed transatlantic demonstration, thesaid demonstration actually took place ; and whileit was calling upon Mr. Baird to, demonstrate tele-visiOn by wireless over a distance of twenty-fiveyards, the Baird Company forestalled the publica-tion of the challenge by transmitting recognisableimages of human faces to the Canard liner Beren-garia,' then 1,500 miles away in mid -Atlantic.Verb sap."

The " Berengaria Experiment."We would, very briefly, point out to our

readers that the " Berengaria " experimentwas a repetition of the first transatlanticexperiment-both meritorious, as we havemore than once stated ; but both experi-ments were beside the point when con-sidered in the light of the terms of- ourchallenge and the reason for that challenge.

We do not propose to weary our readerswith another recapitulation of the reasonsfor our challenge. Perhaps the only com-ment necessary is one which was publishedby " The Electrician " (March 16th), withwhich we entirely agree :

Popular !Fireless, April 21st, 1928.

" The Electrician " stated (inter alia): " We havenothing but admiration for the progress that hasbeen made, so far, but do not favour the publicitymethods that are at present being employed. . . .In the case of the transatlantic success; we canhardly imagine the disgust of the American .news-papers at having missed such a 'scoop.' Now, althoughthis kind of thing may have publicity value, it iscalculated to undermine the confidence of those whoare looking for evidence of definite scientific achieve-ment, and when the complaint is made, as we haverecently seen it in print that Mr. Baird's work Iscriticised in ' certain quarters,' we feel that Mr.Baird has only himself to thank, for having acted ina manner which provokes distrust. We do not thinkthat commonplace home television can be expectedfor some considerable time to come. The systems ofwhich we have knowledge appear to be either tencrude to be of more than experimental interact, or -7-else, where some higher degree of success has beenattained by way of results, the cost has been pro-hibitive."

" A Final Word."And, as a last quotation, we print in

full (with acknowledgments to our con-temporary " The Electrician ") a completeparagraph, entitled " A Final Word,"which also appeared in the issue datedMarch 16th :

" We believe that television will develop alongparallel lines with radio broadcasting. As we pointedout in these columns three weeks ago, there seems tobe nothing to stand in the way of the ultimateachievement of television as a practical service tohumanity, within a reasonable space of time, by oneor other of the several systems which are at presentbeing developed. We must, however, guard againstpermitting ourselves to be influenced unduly by theoptimistic statements of those who, in their enthu-siasm, see the ultimate goal of their experimentalefforts long before it has become visible on thehorizon. Every scientist who respects his reputationshould take steps to ensure that what he puts onrecord regarding his scientific achievements shall notbe distorted and exaggerated by others who mayquote him. Even so far back as 1920 Mr. Baird madea statement to the Press that he anticipated that his' televisors ' would be available to the public beforethe end of 1927, and at the Radio Exhibition lastyear went so far as to exhibit a number of boxeslabelled ' Baird Televisors.' Good ptiblicity weagree, but in a form which can hardly be expected toinspire lasting confidence."

Nothing more need be said, except thatwe express the sincere hope that whennext Mr. Baird and his advisers see fit toannounce the details of future televisionexperiments, they will bear in mind theadvice given by The Electrician "-whichwe, in all friendliness, and with a desireto see British Television development leadthe world, heartily endorse.

The scene aboard the " Berengaria " when, it is claimed, an image was received from London via Television.Mr. Hutchinson of the Baird Television Development Co., Ltd., is en the extreme right.


THERE seems to be something almostmagical about the name "Chitos " tomost POPULAR WIRELESS readers, a

fact which is not altogether surprising whenone remembers how extraordinarily suc-cessful this highly -sensitive little set hasproved in the hands of home constructors.Probably it is no exaggeration to say thatit has done more than any other circuitto convince experimenters that real long-distance reception is actually possible withquite a simple set, and without using suchultra -freakish circuits as the. Armstrongsuper -regenerative, Flewelling, and so on.

Special high sensitivity single - valvereceivers certainly are fascinating, and the" Chitos " is a particularly good specimen ofsuch a circuit, being almost free from thevices usually associated with them, andmoreover, quite easily handled in mostcases. True, there is usually some slightdifficulty in finding just -the right size ofreaction coil for best results, but when thatdifficulty has been overcome, and it is notas a rule a very troublesome matter withone of the later " Chitos " designs, the set ispractically as easy to operate as any othersingle -valve reaction set.

On Long Waves.The recently -published 1928 version of

this receiver has attracted considerableattention and seems to be proving verysuccessful in readers' hands, although therehave been one or two cases of difficulty ingetting good results on the upper wave-band (5 X X and so on) since the " Chitos"circuit in general does not appear to bequite so effective here as on the ordinarybroadcast range. A little experimenting

1 Ebonite panel, 12 in. x 8 in. x in.(any good branded nriterial).

1 Cabinet, 12 in. x 8 in. x 8 in. deep,complete with baseboard and brackets(Arteraft, Bond, Cameo, Caxton,Makerimport, Pickett, Raymond, etc.).

1 L.F. transformer (Lissen in set. Any< good make).

1 2 -way coil holder with long handle(Lotus, or similar type).

1 0005 mfd. variable condenser (Cyldonin set. Any good make).

1 Plain or vernier dial (vernier ad-vised).

g 1 -0003 mfd. fixed condenser (Clarke,Dubilier, Igranie, Lissen, Milliard,T.C.C., etc.).

11111t11111111111111111111I1111111111111111111411111111111111111111111111111111111

* 4.--4-.-4-4-0.-.--4.------.....-4-4.4-4-4.-*A " Chitos " set needs no introduc- 4don, for every "P.W." reader will at 4leasthaveheardof thisfamous"P.W." 4

tcircuit. Here we present a right -up- 4to -date two -valve version-a simple, tinexpensive set which probably givesjust as much in the way of results as

it is possible with two valves.By the "P.W." Research Department.

* *with coil sizes, etc., seems to get over thisdifficulty, and in general the new set seems

to be in a fair way toachieve very wide pop-ularity.

It is only natural,therefore, that weshould receive manyrequests to publish adescription of the pro-cedure to be adoptedwhen adding low -fre-quency amplification tothis set, either as aseparate unit or as acomplete new design.

A special design has accordingly beenproduced with the addition of one low -frequency stage, which should meet thecase quite well, since it will show the moreexperienced constructor how he can, ifdesired, add not onlyone but two stages.

In producing this special design we havekept in mind the requirements of thosewho may already possess the single -valveversion and desire to convert it into a two -valve receiver, keeping as far as possible tothe original scheme. As a matter of factthe work has been done by taking theoriginal set, rearranging the lay-oht of theparts on the baseboard slightly; and simplyadding the necessary parts required to formthe low -frequency stage. This has beendone on the original panel and baseboard,since the extra space involved is not great,and the original lay -out was one in whicha good deal of space was deliberately wastedin order to allow for various sizes of com-ponents, ease of construction, and so on.

Loud -Speaker Work.Thus, you will find it is quite possible to

convert your existing single - valve 1928"Chitos " to the two -valve version, so addingthe extra valve which you desire for workinga loud speaker on the local station, 5 G B,and perhaps a few foreigners. All otherstations within reach will, of course, comein very much more strongly on the head-phones with the addition of the extravalve, so that you will no longer need toobtain such a critical reaction adjustment,but on the contrary will be able to use a littleless reaction and thus be able to gain bettersignals without the woolliness associated


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COMPONENTS REQUIRED.1 Giid - leak holder and 2-meg. grid

leak (Dubffier, Igranie, Lissen, Mill-iard, etc.).

1 Panel - mounting 6 -ohm rheostat(G.E.C. in set. Any similar type,Igranie, Lissen, etc.).

2 Sprung valve holders (Benjamin, Bow-yer -Lowe, B.T.H., Burndept, Burns -Jones, C.E. Precision, Lotus, Marconi -phone, Pye, W.B., etc.).

1 Reaction control resistance (see text).9 Indicating terminals, markings as per

diagram (Belling -Lee, Clix colouredtype, Eelex, Igranie, etc.).

Quantity of Glazite, Junit or tinnedcopper wire and Systoflex.

284

THIS YEAR'S " CHITOSTWO"

(Continued from precious page.) t

with the use of intensive reaction. Further,in searching for distant stations, there is lessrisk of oscillating, since you will be able topick up weaker signals, and need not bringthe detector so near to the edge of oscillation.

A Simple Circuit.For the benefit of those readers who will be

constructing this set as their first adventurein the " Chitos," it may perhaps be usefulto explain that the arrangement is quite asimple one, consisting essentially of a series -tuned aerial circuit, with the tuning coilon the aerial side of the condenser insteadof in the reverse position, which is the con-ventional one. The grid and filament ofthe valve are connecte in effect across thetuning condenser instead of across the coil.

The earth connection, also, is a slightlyunusual one, since instead of being takendirect to the filament, it is taken to a pointon the anode circuit, for reasons connected

1. with ifie pickinsfup oflong -wave s o n swhen they are:liot re-quired, a point whichwill be well understoodby those who have ex-perimented with dif-ferent forms of " Chitosl!and noted the extremeannoyance of hearinghigh - speed automaticMorse superimposed onthe shorter wave broad-casting station they aretrying to receive. Plainmagnetic reaction isused, controlled mainlyby means of a swing-ing coil, and usuallyaccompanied by someadditional adjustmentsuch as a variable grid condenser, variablegrid leak, variable resistance in series withthe reaction coil, and so on.

A glance at the circuit diagram will makeall this clear, and you will ace that the two-valver that we are now dealing with issimply the original 1928 circuit with theaddition of a plain transformer - coupledL.F. stage, with the exception of just one

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simple modification in the reaction circuit.It may be remembered that in the singlevalve version a supplementary control ofreaction is obtained by placing a variableresistance in series with the anode circuit,this resistance being of the type commonlyemployed for varying the voltages obtainedfrom a mains eliminator. A suitable resist-ance, of course, is the " Braley -ohm "obtainable from Messrs. Rothermel Ltd.,

(Goninued on next page.)

POINT-TO-POINT CONNECTIONS.Filament contacts on the valve holders

V, and V., nearest to each other joinedtogether, to one end of the grid -leakholder and to one side of the panelrheostat.

Other side of panel rheostat to theL.T. + terminal.

Remaining filament contact on thevalve holder V, to the H.T. - and LT. -terminals, to the G.B. + plug via aflexible lead and to the remainingfilament contact en the valve holder V.

Other side of grid -leak holder to thegrid of V, and to one side of the -0003mfd. fixed condenser.

Remaining side of the -0003 mfd. fixedcondenser to the fixed vanes of the.0005 mfd. variable condenser and tothe plug of the fixed coil holder.

Socket of fixed coil holder to the aerialterminal.

Earth terminal to one side of themoving -coil holder via a flexible lead, tothe moving vanes of the -0005 mfd.variable condenser, to one side of thereaction control resistance (marked" R " on diagrams), and to the " IP "of the L.F. transformer.

" OP " of the L.F. transformer to theH.T. + 1 terminal.

" OS " of transformer to the grid ofV_.

" IS " to the G.B. - plug via a flexiblelead.

Plate of V, to the remaining side of themoving -coil holder via a flexible lead andto the remaining side of the reactioncontrol resistance " R,"

Plate of V. to the L.S. - terminal.L.S. + terminal to the H.T. ± 2

terminal. This completes the wiring.NOTE. - The moving - coil holder

accommodates the reaction coil. If theset does not oscillate when the reactioncoil is brought nearer to the aerial coil,and the reaction control resistance isscrewed " out," try the effect ofreversing the leads to the moving -coilholder.

:7.'11 1111 I I I I I I I I I I I I I I I 1 I I I 1111 I I I I I I I I I II I I I I I I I MI I I I I I I I I I I I Fr:


THIS YEAR'S " CHITOS tTWO."

(Continued from previous page.)*

Messrs. Hamley Bros., and others. Thehct of varying this resistance was reallyalter the high tension applied to the

detector valve within quite wide limits,provided that a suitable Bramleyohm orsimilar variable resistance was chosen. The

The detector alve should be one -of thespecial H.F. o special detector types and,of course, you can use either the 2- or6 -volt type. Tyo-volters work quite wellin this circuit, although; of course, if youwant theltvery finest results obtainable,naturally you would use the 6 -volt type.The economy of the 2-volters, on the otherhand, is a very weighty point to somepeople. By the way, both the detector andthe L.F. valve should. be of the same fila-ment voltage, since they are controlled bya common rheostat on the panel, which also

serves the purpose of anon -and -off switch. Forthe second socket youwill require a smallpower or L.F. valve;preferably the former, ifyou require good qualityon the loud speaker, andyou should be very care -hit to adjust the gridbias to its correct valueaccording to the makers'instructions for the par-ticular H.T. voltagewhichis being employed.

The high-tension vol-tage on the detectorvalve should really befound by a little experi-menting, since it is natu-rally rather critical in aspecial circuit. Some-where about 60 Ito 70volts will usually becorrect, since the " Chi-t os " seems to appreciatea rather higher value ofH.T. than most othersimple detector valvecircuits. Mn the other

valve, of course, it is a. safe'rule;to.apply asmuch H.T. as you can, up' to the' safemaximum rating of the valve which isbeing used, which is usually abceut 120 volts.If you want the best results, you shouldreally make it a rule not to use less than

A back -of -panel view of the set taken immediately after it had passedthe searching tests " on aerial conducted by the " P.W." Research Dept,

actual value for this control is not at allcritical and as long as you can obtain avariation from quite a low resistance up toperhaps 10,000 ohms it will serve the pur-pose. For example, the Bradleyohm typoNo. 5 E is quite suitable.

In the two -valve version it has beenfound better, in order to meet the require-ments of the L.F. stage which follows, nitto vary the H.T. on the detector valve inthis way, but to connect the variable re-sistance instead directly in parallel with thereaction winding.

For this purpose the 1 E Bradleyohm isalso silitable. Then, take a fairly large re-action coil, say a 75, (a 50 if the valve isone which oscillates readily), place thisfairly close to the :tuning .coil, say only aninch or so away, and screw .down the re-sistance until the set ceases to oscillate.Quite a wide control of reaction can thenbe obtained with the resistance only, andthis will 'suffice for most tuning operations;but, of course, it can be supplemented byvariations of coupling between the coils,since a two -coil holder is used.Constructional Details.

The constructional details of the set willbe followed quite easily from the wiringdiagram and the photographs, and there islittle which can be said which would helpthe constructor. It is a perfectly straight-forward job of fastening down componentsand wiring up according to the diagrams,and it will probably be far more helpful todevote the remainder of our time to theconsiderations of practical operating de-tails, since it is more often here that diffi-culties arise with these special circuits,

100 volts, although, of course, for head-phone work much lower voltages are ade-quate. A higher voltage is really called for,however, when you try to get really goodquality on your loud speaker.

One of the most important points whendealing with a "Chitos is to get your coilsizes correct, and you should provide aNo. 50, 60, 75 and 100 for work on theshorter broadcast waves. In the aerialsocket you usually require either the No. 75or the 100, according to the range you areworking on, that is to say, whether on theband of waves below 400 metres or theband above thisfigure. For reaction, aNo. 50, 60, or 75;should be tried, and youwill soon find the one which gives the bestcontrol over the whole tuning range. Alittle experimenting here will soon show youthe best size to obtain really smoothreaction, not forgetting, of course, thatdifferent values of H.T. should be tried atthe same time on the detector valve.

Long -Wave Coil Sizes.For the longer waves you will require a

fairly large size of coil in the aerial circuit,and may meet with a little difficulty insecuring the best value. - As in all series -tuned circuits, one coil does not give a verywide tuning range, therefore you may findit best to try more than one size until youget the best results. Usually a No. 200will be correct, but you may need to try'even a higher value than this, while a No.1150 will usually be correct for the reaction,'although you may find it advisable to in-crease the value of H.T. on the detector,valve a little when experimenting on thelong waves.

These warnings are given when dealingwith the long -wave band because it is,gathered that readers report trouble withtheir " Chitos " receivers on the long waves,'if trouble is reported at all. As a matter offact, you are not likely to get any troublewith the 1928 version, with its specialsupplementary reaction control, which prac-tically eliminates these difficulties.

One of the features of the famous " Chitos " circuit is that it makes the optimum use 01 reaction effects.The moving -coil holder, which can be seen above, and a variable resistance, are the essential reaction controls.


AN EASILY -MADEPLUG.

READERS of " P.W." who may havesome old valves on hand with ebonitebases will find that excellent plugs

for both electric light and wireless usecan readily be made from them, as shownin photo. Two prongs should be cut away,and the ends of the flex bared and slipped

.tin side the re-maining twoprongs until flushwith the tips. Adrop of solder isnext placed on,which will holdthe flex securelyto the prongs.

The soldershould be gentlyrounded off witha fine file, so thatthe plug will slipsmoothly into thesocket. Finallythe base of theplug is filled upinside with somemelted sealingwax procured

from an old dry battery. (This will preventa possible short circuit between the flex andalso give greater rigidity to the job.)

The simple device describedin this page.

A PLUG-INFUSE -HOLDER.

THE insertion of a fuse in series withthe mains is a precaution which youshould never neglect when you make

up a battery eliminator. To avoid therisks attendant on short-ericuits, you willdo well to fit fuses which will carry the

urrent required with a margin of safety ofsay, 25 per cent. ,

You can, of course, purchase fuse boxesfor the purpose, but these are usuallydesigned to hold fairly heavy gauge wire.Fuse wire to carry only small currents,. 1ampere or less, is delicate stuff to handle.If you want to put in fuses of this rating,you can easily make holders out of standardebonite coil plugs.

In a coil plug make two cuts with a saw,about -11,th-in. deep, as shown in Fig. 1.The cuts meet at the top of the plug. Fixone end of the fuse wire under the bolt

head on one side, putting washer over thewire, screwing the bolt ho e until it onlyjust grips the wire, or th latter will bedamaged. Carry the wire round the V-shaped groove, and fix the other end underthe second bolt head. See that there isenough tension on the wire to keep it inthe groove.

If the fuse " blows," the wire will meltat the apex of the V, and the ends will besure to separate. As the wire is in agroove, the holder can be handled withoutfear of damaging the wire. A baseboard -mounting coil plug, fixed in the eliminatorunit, provides the means of plugging in thefuse.

USING THE"ANTIPODES ADAPTOR"

ALONE.

FOLLOWING upon the publication ofthe " Antipodes Adaptor," in " P.W."No. 303, a query has been received

asking if the unit can be used successfullyon its own as a single -valve short-wavereceiver. This happens to be quite apractical proposition, and since the subjectis one likely to he of interest to other readers,details are given below for " adapting theAdaptor."

It will be remembered that in theoriginal unit, the H.T. and L.T. supplywas obtained from the set proper, and,therefore, to use it alone it is necessaryto make some provision for the battery and'phone connections.

The most simple and convenient methodis to mount a valve holder and terminal

strip on a small piece of wood, connectingup as shown in the diagram. If it is -desiredto use a resistance in series with the filament,this should also be mounted on the base-board and joined in series with the filamentand L.T.

The plug from the unit can then beplaced in the valve holder, and with theusual battery and 'phone connections made,the method of procedure becomes exadllysimilar to that described in the originalarticle.

It should be understood, of course, thatonly under exceptional circumstances willthe Australian stations be heard on the

single -valve arrangement, but there is everypossibility of receiving some of the morepowerful American stations.

For those who have made, or are makingthe unit, this small modification should beof interest, since it will enable the unitto be tested for oscillation, etc., before itis coupled to the amplifiers of the set.

AMERICAN VIEWSON TELEVISION.

WE reproduce below an illuminatingextract from a recent interview,granted by Dr. Lee de Forest-

inventor of the three -electrode valve-to Mr. Hugo Gernsback, Editor of the

Radio News."MR. GERNSBAGK

What are your views on television, in viewof the past experiments by Baird of London,and by the research engineers of the AmericanTelegraph .1: Telephone Corporation Doyou believe television attachments to radiosets a matter of the near future? If so, howsoon ?

DR. DE FOREST : I am quite naturally in-terested, and have inspected the work intelevision which has been carried on in'thiscountry, particularly that by the AmericanTelegraph & Telephone Corporation. Imust pay the highest possible tribute to theingenuity and patient research which hasmade possible the system employed by theAmerican Telegraph & Telephone Corpora-tion. It is little less than a scientificmiracle. Nevertheless, I know my views ontelevision have been somewhat disappoint-ing to those who wish to believe that in thenext few years every one can have a mov-

ing -picture show at home, broadcast directfrom his favourite theatre. Frankly, Icannot foresee such a millennium for theradio fan. Until some radically new dis-covery has been made in physics, some newprinciple or operation of which we to -dayhave no clear conception, television appara-tus must continue to be extremely intricate,delicate, requiring the constant and mostcareful attention of highly -skilled experts,and be built and operated at very greatcost. Until such a new discovery, therefore,I think we must limit our television ex-pectations to an occasional demonstrationunder the auspices of one of the few greatelectrical engineering and manufacturingcorporations. Television in the popularmind means radio broadcasts of distantscenes as they transpire.

" General Gullibility."I have little patience with some of those

whose names are associated with the historyof this new development, who seem willingto impose on the gullibility which the publicevinces whenever the word " Television "is used. A few years ago it was impossibleto get anyone to believe in wireless tele-graphy, and later in the possibilities of thewireless telephone. Of recent years, how-ever, the progress in popular science hasbeen so phenomenal that general gullibility,or willingness to accept any prediction alongthe lines of invention, takes the place ofthe scepticism which formerly made thework of pioneers so difficult.

Popular. Wireless; April 21st, 1928. ' 287

T EXPECT that you, in1 common with most other

radio enthusiasts, havetwo or three spare wirelessparts which are not in use.Possibly a fixed condenser,or a potentiometer whichcame off your old set, orsome old - fashioned plug-incoils of the type now out offavonr.

Perhaps it has neveroccurred to you that in oneor more of these parts .therelies the possibility of betterreception free of charge.Whatever the circuit you maybe using, unless it is an ultra -modern andup-to-date one, it is probable that you can;by the parts taken from the junk box,effect an improvement in reception.

As explained -in this article, the numbers show wherespare components can be used to improve an ordinary

one -valve reaction detector.

Look, for instance, at the diagram givenabove, which shows the connections of adetector valve employing capacity - con-trolled reaction of the " Reinartz " type.This circuit, whether used as a single-valveror followed by one or more stages of low -frequency amplification, is undoubtedlythe most popular arrangement of connec-tions to -day.

Uses for Fixed Condensers.Against certain of the leads are drawn

figures, 1, 2, 3, 4, etc., and these numbersindicate the places where the junk -box islikely to be of use. Suppose, for instance,'that you have on hand a small fixed con-denser. If you have never tried the effect ofconnecting it in the aerial circuit at thepoint marked 1, you certainly should tryit to -day, especially if you live fairly closeto a broadcasting station. Very often agreat improvement in selectivity resultsfrom this simple alteration, especially incases where a low or badly -screened aerialis used.

A *0001 or a .0002 mfd. fixed condenserwould have been eminently suitable forthe foregoing trouble, but if your con-denser is a larger one, say .001 or -002 mfd.,its effect upon selectivity would not bevery marked. It might, however, do somevery good work at the point marked 2 onthe diagram. A glance at the diagramshows that one side of the reaction con-denser is connected through the coil toL.T. and hence to H.T. negative, whilst

USING THOSESPAREPARTS

Some practical suggestions for improving reception free of cost.

the other side is connected to the plate ofthe valve and via the choke to H.T. posi-tive. In other words, this condenser isdirectly across the H.T. battery, and if itsplates become a little bent, or a speck ofdust falls upon them, the battery mayshort and damage itself, or certainly damagereception. If, however, the lead fromcondenser to plate of the valve is brokenat the point marked 2, and the spare con-denser is inserted there, this will act as acomplete safeguard. The control of reactionis apparently unaffected, provided that thecapacity of the fixed condenser inserted atthe point 2 is a good deal larger than thevariable condenser that controls reaction.

Increasing Sensitivity.If you have a potentiometer on hand

and you are interested in long-distancereception, you may be able to increase theDX range of your set considerably, by aslight alteration to the grid -leak connec-tion. In some sets one end of the leak istaken to L.T. negative, and in others tothe L.T. positive lead, and the connectionthat may be best for one valve may bebad for another one. If you have a potentio-meter on hand and connect it across theL.T. lead at the point marked 3, you havea ready means of increasing the sensitivityof the set.

That end of the grid leak which is con-nected to the filament wiring should bedisconnected from there and a lead takeninstead from the grid leak to the slider ofthe potentiometer. One end of the poten-

tiometer winding will go tothe L.T. negative lead andthe other end to L.T. posi-tive. By Moving the sliderthe grid leak can then, ineffect, be made to go to L.T.negative or positive, or toany intermediate point atwill. It is amazing how weaksignals can be " nursed" intostrong ones by this simplealteration.

Finally, if you have someold large plug-in coils onhand, you may find that they.would make a better chokethan the H.F. choke itself.

Very often a plug-in coil of 200 or moreturns can be put in place of the H.F.choke, and will give a far better controlover reaction. This, again, is an im-provement which will be more especiallyappreciated by the long-distance listener.

RADIOI ITEMS OF INTEREST.

In the last nine months of 1927 the broad-casting revenue collected by the Post Officeexceeded expenses by over £65,000.

The tuning -fork used by the B.B.C. todetermine broadcasting wave -lengths wasrecently taken to Brussels by air liner to becompared with Europe's standard tuningfork.

Telephone subscribers in any part of thiscountry can now call up and communicatewith Canadian subscribers by means of thetransatlantic telephone service, via Rugby.

The Malabar short-wave station, DutchEast Indies, is now broadcasting fairlyregularly on Wednesdays, Fridays, andSaturdays, from 1 to 4 p.m. G.M.T.,on a wave -length of 17.4 metres, with thecall sign A N P.

* *

The Cardiff Station holds the B.B.C.record for the minimum number of break-downs during 1927.

The sensitivity of a set of this type can often be increased by a potentiometer, as explained above.


TECHNICAL NOTES. By Dr. J. H. T. ROBERTS, F.Inst.P.

t USEFUL BATTERY INDICATORSDOWN TO 6 METRES-"ACTION AT A DISTANCE," ETC.

'Useful Battery Indicators. -

IWAS talking some little time ago aboutindicators for showing the state of chargeor discharge of the L.T. battery and in

this connection I received a few daysago, from the Eagle Engineering Company,one of their Chakophone accumulator -capacity indicators which they have sentme for inspection and test. The instru-ment is about 21. in. in diameter, and ismade in two models, one a switchboard type(" baseboard type," as it would be calledfor wireless purposes) and the other aflush -fitting type (a " dashboard " typefor motor cars, or " panel " type forwireless).

The instrument is, of course, in effect avoltmeter, but the dial, instead of indicatingvolts, indicates in three sections marked" low," " medium " and " full," thesesections being differently coloured forready identification. A small press -buttonswitch is provided on the instrument,which is to be depressed when takinga reading: in the ordinary way, there-fore, the instrument is not connectedin circuit.

Closed Circuit Readings.This little instrument has been thoroughly

tried out and is not only very convenientin use but seems to be quite accurate andreliable. Of course, it has to be madein three models for 2 -volt, 4 -volt and 6 -volt accumulator batteries and it is madein H.T. models for voltages of 60, 72, 90,100, 120 and 150 volts.

In taking a reading of the battery it isdesirable not to take the reading on opencircuit, but to throw in an average load-this may be done by the simple process ofswitching on the valves of the set: thereading obtained at normal load gives amuch better idea of the working conditionof the battery. If a trickle -charger is usedin conjunction with the battery the indi-cator will be found very useful in avoidingovercharging. An incidental advantageof this instrument is that it is not polarisedand, therefore, it does not matter which wayround the battery leads are connectedto the instrument terminals.

Depends on S.G. of Acid.The accuracy of the reading and the

calibration is stated to be correct so longas the charge rate and acid density specifiedon the battery are adhered to.

I can recommend this instrument asbeing really a very useful little accessoryindeed.

By the way, in case you should changeyour battery to one of a different voltage(whether H.T. or L.T.) the makers of theinstrument have an arrangement wherebyyou can send back the instrument andreceive another one of the required voltageon payment of a small charge for theexchange.

Down to 6 Metres.The General Electric Company of America

have been carrying out some extraordinaryexperiments with high -frequency currents,in their famous laboratory at Schenectady,and they sent me an account of these testsa week or two ago. Everyone knows thatwith high -frequency oscillatory currentsit is possible to obtain something approxi-mating to " action at a distance," and theeffects which are described in the GeneralElectric Report really amount to a number

of curious instances of these high -frequencyinfluence effects. An incandescent laniptaken from its carton for the first timelights to full brilliancy without wires orsocket when brought within a few feet ofthe H.F. circuit operated by the new high -frequency valve.

" Action at a Distance."A copper bar lying on the floor blisters

the hand that picks it up, although themetal itself is cold. A neon tube glowsbrilliantly when merely touched by aspectator, meters in adjacent rooms runwild, and measuring instruments are twistedor broken so thalk all accurate scientific workin the immediate vicinity is impossible.Investigators coming close to the newapparatus suddenly feel a comfortablewarm glow "reminiscent of prohibitedstimulants " (as the Report says) :

" This 6 -metre valve has nothing new inprinciple," said one of the engineers engagedin its development. `,` Very short radio

(Continued on page 306.)

sA

This is a front -of -paneview of THIS YEAR'S" CHTTOS " TWO, whichis fully described elsewherein this issue. The original" Cbitos " receiver was des-cribed exclusively in " P.W."and attained phenomenalruccess as a simple andeffective distance - getter.

NEWS FROM SAVOY HILL. FROM OUR OWN CORRESPONDENTS.

ANOTHER WELSH ROWPOLITICS BY RADIO-B.R.D.A. REVISED, ETC.

Another Welsh Row.IT was understood that the B.B.C. hadI squared their troubles with the Welsh,

especially since the establishment ofthe National Orchestra of Wales underbroadcasting auspices. But apparently aspecial commission of the Welsh, appointedto keep 'an eye on broadcasting, has beeninformed that the B.B.C. propose to doaway with the regular series of relays ofWelsh programmes on 5 X X. So the fat isin the fire again. The Welsh were particu-larly proud of the 5 X X relays, partly be-cause of their Continental range. It isbelieved that Mr. Lloyd George himselfproposes to take a hand in the renewedstruggle.

Politics by Radio : A B.B.C. Dilemma.Having secured permission to put out

controversy carte blanche, Savoy Hill is

-4.-4.- -------.11.*encountering difficulties in execution. Tobegin with, there are the negotiations withthe Parties. It is believed that Labour isthe keenest to get a chance at the " mike " ;whereas there are signs of reluctance onthe part both of Conservatives and ofLiberals. The latter have asked the B.B.C.to outline fully its plans for the develop-ment of controversy on the political side.But the B.B.C. is wisely non -committalexcept for the initial experiments There-fore it is just possible that some of theParties may not take advantage of theopportunity now offered.

B.R.D.A. Revised.The proposal to do for radio what the

Electrical Development Association hasdone for the electrical industry bas just beenrevived, this time from the trade angle, and


Popular Wireless, April 21st, 1928. `289

NOTHING so much marsthe appearance andoften the efficiency of

a set as poor soldering. Eitherthis is due to carelessnessor insufficient knowledge,but in each case the finishedreceiver in appearance andefficiency will in no wayequal the set in whichsoldering has been reallywell carried out.

Soldering may seem asimple job, but if realefficiency is to be acquiredin the art of doing it properlythere are certain methodsof procedure which must befollowed for the bestresults. Having once master.ed these few points thereis nothing much in it.

Considered theoretically soldering is amethod of obtaining a homogeneous andcomplete metallic contact between anytwo surfaces of metal. For this a " flux 'is necessary, its purpose being to makechemically clean the surfaces of the metalsto be joined, over which the molten solderwill then " run," effectively welding thetwo together. The action of a flux isto dissolve the thin layer of oxides andsulphides present on the metal to besoldered, and unless this film is removedthe solder will not unite with the metalsto be soldered, however hot the iron.

The Main Requirements.The basic requirements for a good soldered

joint are, therefore, a flux to clean the metalsurfaces, and a clean " iron " with whichto apply to them sufficient molten solderto flow over the joint and form a strongconnection when cold.

Now, success in soldering depends to agreat extent upon using the right size ofiron, the right flux and the right solder.It is very easy to use the wrong thing forany of these so that. the choice of materialsis important.

There are several varieties of solder, whichare an alloy of lead and tin. The greater theproportion of tin in the solder, the flower itsmelting point with an increase in softness.Some kinds of solder are too hard andothers too soft. The best material forwireless purposes contains about two partsof tin to one of lead. It is bright in appear-ance and when a stick of it is bent near theear a faint crackling noise, the " cry oftin," should be heard. This solder meltseasily, runs well and makes a good joint.It is best obtained in thin sticks, as in thisform less heat will be absorbed from theiron when melting it. Resin -cored solderis preferred by some constructors, as thiscombines flux and solder, although alljoints must be scraped clean before solder-ing is successful with this material.

Choosing an Iron.In regard to " irons," the larger the

copper bit, the longer will it hold its heat.For the heaviest work required in wirelesswork, the copper bit should not be largerthan about in. diameter by 3 in. in length.For the major portion of the work a smalleriron having a bit up to I in. by 2 in. is veryuseful as it gets hot quickly and retains itsheat long enough to make several joints.A smaller hatchet iron is also extremelyuseful for delicate work.

* 4. -4.41.41--0-0-4.41,..4-41,-4.-4.-4.*

" There are certain methods of pro-cedure which must be followed for best

results."An article of value to all set builders.

By L. FRENCH.*

Now, before commencing a soldering job,the iron, whether it has been used beforeor not, should be well cleaned and tinned.The four faces of the bit should be filedbright with an old file specially kept forcleaning irons. ThiS removes surface dirt.The iron is then heated and again brightenedup with the file as quickly as possible, rubbedwith flux and then with a stick of solder,when the four faces will be nicely tinned allover. The iron is then wiped with a ragto remove flux and surplus solder. After

The solder should be placed in contact with theiron and the metals to be soldered, when a big

Joint is to be made.

reheating, and another rub of solder theiron is ready for work.

In cleaning the iron the application offlux can be made by dipping momentarilyin a saturated solution of zinc chloride(" killed spirits "), rubbing on resin or apatent flux, or by rubbing the iron on ablock of sal -ammoniac. The latter methodis best, but gives rise to a certain amount

of fumes. In my opinion,other than sal -ammoniac,the best material is a patentflux such as the well-known" Fluxite."

Before leaving the subjectof the iron, the method ofheating is important. What-ever the source of heat aniron should never be allowedto get red hot. For thisreason a gas flame gives thebest regulation of heat, whilesuch a flame does not tarnishthe iron like a coal or cokefire. The temperature of theiron can be judged from thecolour of the flame whichwill become tinged with avivid green as the copper bitnears red heat. The iron willnot be hot enough until

a trace of green appears. Alternativelythe tinned surface can be watched. Ifthe iron is overheated this will becomevery dull. Overheating an iron meansthat the process of cleaning and tinningmust be done all over again.

Use Gas or Electricity.Heating an iron in a coal fire is not very

satisfactory, but where there is no alterna-tive a cylindrical wrapping of thin sheetiron or tinplate should be made about 6 in.long and slightly larger in diameter thanthe iron. This cylinder is placed in thefire, and the bit inserted in the centre ofthis sheath. This prevents the iron, to agreat extent, from becoming tarnished,although overheating must be carefullyguarded against.

When a mains supply is available anelectrically -heated iron is a very usefulthing to have, while it is not expensive torun. It is both clean, and convenient,while it can be kept continuously at theright temperature and will not over heat.

When the receiver comes to the benchfor soldering up, all contacts and connec-tions should have been previously cleanedup as described in the section on wiring.Now have near you the gas flame if con-venient, iron, solder, flux, a clean rag anda pair of pliers. All being ready all solder-ing tags should first of all be tinned. Alight smear of flux and a touch with a hottinned iron will do this, any excess of fluxbeing wiped off immediately with a clean,soft rag.

Preparation Important.Then put two or three wires in position

and solder up with one heating of the iron,which should carry enough solder on itsnose for half a dozen joints. If the wirehas been prepared, as described previously,no flux should be necessary. Should thesolder not run cleanly, the merest trace ofFluxite may be applied to the joint, andafter soldering wiped off before cold. Tomale a proper joint the solder must runlike water over the metal.

Soldering is an easy job if all these pre-parations have been made, as one can goright through the receiver without anylengthy pauses in between to fit wires andstruggle with joints that won't " run "The essential preparations are to cut and fixin position all or nearly all the wiring.Then tin all tags and contacts, and a touchwith a hot iron at each joint completes thejob.

Popular Wireless, April 21st, 192b.

" SECRET FORCES " AND TELEVISION.The Editor, POPULAR WIRELESS.

Dear Sir,-You say that my statement, " It isnecessary for the public to know of these two secretand powerful groups which are playing ducks anddrakes with the fortunes of television," calls forex planation ; you shall have it.

I repeat that there are these forces-hardly de-finitely organised, but present nevertheless-andthey are secret to the public who do not know ofthem. The editorial standpoint of POPULAR WIRE-LESS might be classed with the opposing force buton the extreme edge of it, and nearest to truth.I am wholly in praise of the £1,000 challenge offeredby POPULAR WIRELESS.

Those who form the most dangerous part of theopposing force, and whom I condemn almost asstrongly as the benighted members of the other forcewho damn Baird with exaggerated praise, are verylargely noted men of science. One is Herr Aigner,in Vienna, whom I have found ready to arguemathematically and at great length that televisioncan never come ; and I am afraid that another ismy friend Professor Arthur Korn, the photo -telegraphy pioneer. There are others in GreatBritain and America. Seldom have these meninvestigated television sufficiently to realise thepossibilities of surprise achievements, and becausethey have done excellent work with X-rays, or insome branch of radio, their words are marked withawe.

I have, already, Mr. Editor, read and enjoyedthe contributions to POPULAR WIRELESS you suggestI should read. I will not agree with you that allknown systems will never achieve popular television,though it is unlikely that they will.

In my lecture I was simply trying to leave thesame impression as you consistently try to give-that the public should wait for proof before believingany exuberant statement about television.

Faithfully,WILLIA3I J. BRITTAIN.

THE " PRIADYNE " CIRCUIT.The Editor, POPULAR WIRELESS.

Dear Sir,-I am writing you with regard to theresults I have obtained when using a one -valve" Filadyne " circuit.

The local station (Stoke) is about one mile distant.From this station I get results good enough to givefair loud -speaker strength. With the use of tappingson the aerial coil I can cover from about 200 metresto 550 metres, and between these ranges I haveheard about twenty-four different stations. Whenthe two -valve circuit appeared in " Modem Wire-less," with choke coupling to the second valve, Imade it up, using a transformer with its primaryburnt out as a choke. On the night I completed theset I received three American stations, but I listenedto one, W G Y, 370'5 metres, so as to take notes ofthe programme. I have now received confirmationof this programme in the form of a card reading :" The General Electric Company acknowledges withthanks your. conmunication reporting reception of arecent progralika rue. Your comments are of distinctvalue as practical contributions to the success of ti is

- * -4.-4-4 -0.*

CORRESPONDENCE

"SECRET FORCES "AND TELEVISIONTHE "FILADYNE " CIRCUIT-THE WORD "ELIMINATOR."

Letters from readers discussing interesting andtopical wireless events, or recording unusualexperiences, are always welcomed ; but it mustbe clearly understood that the publication ofsuch does in no way indicate that we associateourselves with the views expressed by ourcorrespondents, and we cannot accept anyresponsibility for information given.-EDITOR.

company's broadcasting and planning of its pro-grammes."

(Signature at bottom) " P.M. Crosiv."I should like you to print these results in your

excellent paper for guidance of others interestedin the " Filadyne."

Yours truly,Stoke-on-Trent. R. W. C.

THE " ANTIPODES ADAPTOR."The Editor, POPULAR WIRELESS.

Dear Sir,-It may interest you to know that usingthe " Antipodes Adaptor " (described in " P.W., 'March 24th, 1923), in conjunction with the " MullardMaster Three," I have managed to hear 3 L 0(Melbourne, Australia). Most of the usual Americanshave also been received during the past week. Theonly alterations to the " Adaptor" were the omissionof the H.F. choke (as the Climax choke in the " MasterThree " goes equally well down to the low waves), andthe substitution of the " Sydney " Two coil, looselycoupled to an aerial coil of 5 turns of 32 D.C.C.wound and tied together in hank form. The methodof mounting the coil is the same as in the " Sydney "Two, with the aerial coil sliding over the former.

Thanking you for such an easy and quick "Adap-tor " for broadcast to short waves.

Yours truly,Waddon, Surrey. A. D. M. WEBB.

THE WORD " ELIMINATOR." -

The Editor, POPULAR WIRELESS.Dear Sir,-With reference to the letter you

publish from BM/CPPH regarding the use of theword " Eliminator," in reference to apparatus whichenables electric current to be taken from the mainsfor use with wireless sets, we should like to point outto him that, as pioneers in the manufacture of thisclass of apparatus, the expression " Eliminator "

has never appeared in our public announcementsor pamphlets.

We, in fact, originated the expression, " High -Tension Supply Unit," and throughout the trade andby a very large public this expression is generally used.

Yours faithfully,F. J. HAnuirrost,

Publicity Manager,Philips Lamps, Ltd.

145, Charing Cross Road, London, W.C.2.

PROGRAMMES ON 'PHONES.The Editor, POPULAR WIRELESS.

Dear Sir,-Glancing through your issue of March17th. I note remarks re H. A. B.'s programme on'phones only, and H. B. G., of Derby's, suggestion.

I do not disbelieve H. A. B. for a moment, as I hada like experience as far back as November orDecember, 1926.

The following may maintain the interest in thisparticular phenomena.

After completion of multi -valve set and commencingtest in upstairs room on indoor aerial, I donned'phones, plugged in, and received signals crystalstrength before switching on any batteries ; afterremoving coils, valves, grid leak, L.T. and H.T.,and disconnecting condensers, signals still persisted.On finding I was able to receive with one 'phonetag laid on wiring, and holding the other tag betweenfingers, I walked over to mantelpiece and refelved2 L 0 news bulletin from a brass candlestick (afterdisconnecting set, aerial, earth, etc.); also from a 1 -in.nail in wall and various other things including the brasskeyhole plate on a wardrobe door in another room.

After experimenting for a few . weeks, I foundsignals could only be cut out by opening mainswitch ; this was apparently induction from themains, and so long as current was flowing in thehouse, signals were received. -

Amplification was tried, but, beyond a slightincrease on earthing one tag, when using telephones,nothing but a powerful hum from the speakerresulted, when trying direct from the mains throughcondenliers and chokes, etc., anything metallic gavesignals ; the bulk of metal had no effect on strengthof signals, a small tack or a brass fender, strengthremained the same. I was inclined-to"the belief thatsomeone on this supply, 240 volts D.C., is using mainsfor wireless battery power. On one occasion I received5 G B off this famous tin tack, clear as a bell, crystalstrength. All these facts conjured up visions of localpower stations receiving brbadcast, and distributing" light music " to its consumers for a small extra fee, aloud speaker plugged into the wall was rather simple.

I should like it to be clearly understood that theseresults were obtained without the existence of awireless set of any description, in the room, thisbeing purposely removed during experiments.

A satisfactory explanation of this phenomenon ofinduction and rectification without the usual appara-tus would be welcome, and I think the publicationof these facts would create a sudden mysteriousactivity among your many readers.

Yours faithfully,S. G. CROWDER, G.I.E.E., M.I.Inst.E.

Harrow.

TRUE" SQUARES."

rkeee see j(

TRUE right angles or " squares " arevery important when marking outpanels, etc. The geometrical method

of drafting a " square " direct on tomaterial with pen or needle scribing com-passes is shown diagramatically. A -Brepresents one side of the' right angle.Arcs are then struck with compasses atC and D at any point along the line, A -B.The line X is drawn through the points atwhich the arcs intersect, which results inthe line Y being at true right angles tolino X.

Temporary paper " squares " may quicklybe made by folding a sheet of paper in halfand placing a pin prick anywhere on thefolded paper. Open the paper out anddraw a line from one pin hole to the other.The result, when cut out, is a handy"square," formed by the line drawn andthe line of fold made in the paper. Sucha method may be used for cutting a per-manent " set square " in celluloid or wood,the paper cut out being first used as a mark-ing -out template. H. B.

BROADCASTBREVITIES. t

The number of hours worked by theLondon Station, 2 L 0, during 1927 was3,562.

During last year the total working timeof all B.B.C. stations was 65,299 hours,22 minutes.

* * *A recent talk on marmalade brought the

B.B.C. no less than 1,500 applications fora recipe.

* * *

It is feared that Indian broadcast" piracy " is on the increase.

TEMPORARYCONNECTIONS.

WHEN re -wiring a sot in which all theconnections are soldered, it is oftenfound that it is only necessary to

disconnect one end of a particular wire.This leaves the wire in question looselydangling from the other end. With asoldered joint it is highly probably that itwill break off when it, is clsired that itshould remain intact.

A simple method of obviating this isshown in the diagram, which is intended torepresent a panel where alterations are

being -made. The wire which is left disconnected at one end temporarily is secured toone of the fixed wires by means of a smallclip, until the constructor is ready to fix theloose end. This simple little device will savea certain amount of time and work. H. B.


DURING the last few yearsthere have been so manyalterations in the designs

of receivers that, judged by thepresent standards, sets whichwere regarded not so very longago as being the last word inefficiency, are now looked uponas more or less obsolete, or, atany rate, rather old-fashioned.To build a completely newset is naturally an expensive matter, andto many people the idea of keeping anold set indefinitely fails to appeal, andso they are unable to decide as to thebetter course to adopt. To sell a setwhich is over two years old entails aheavy loss, as the depreciation on alltypes of wireless apparatus is far greaterthan on any other item in the householdeffects.

The alterations which arc required tobring a set of the type under discussioninto line with the trend of modem designwill not prove so formidable as one wouldat first suppose. In many of these receiversthe L.F. side of the set is quite capable ofgiving a tone and purity which will com-pare very favourably with the average up-to-date equipment if a good loud speakerand modern valves are employed.

Common Troubles.The trouble will usually be found in the

tuning and reaction circuits, which may notbe sufficiently sensitive or selective totune -in and hold the stations which shouldbe heard on any really efficient set havingtwo or more valves, in these days of powerfulbroadcasting. This is particularly notice-able in the case of magnetic reactioncircuits having the moving coils mountedexternally ; as soon as the hand is movedaway from the handle of the coil holder, thestation, if it has had to be tuned with anydegree of fineness, will often fade out,owing to a slight hand capacity, which mayalso affect the tuning of the variable con-denser.

This sort of thing is apt to pall veryquickly, and leads eventually to an apatheticattitude towards wireless, becoming respon-sible finally for the set being permanentlytuned to the local station.

We will suppose, first of all, that the setto be altered is a straight three-valver,employing magnetic reaction ; the two-waycoil holder is mounted on the baseboard.

Bringing your set up to date.From A " P.W." READER.

The theoretical connections of the detectorcircuit are bound to be fundamentallysimilar to those shown in Fig. 1, in whichLi is the A.T.I., Cr the A.T.C., and L2 thereaction coil.

To alter this so that it conforms withthe circuit shown in Fig. 2 is not goingto be at all difficult. In the first place,the two-way coil holder is removed, andtwo single -coil holders substituted. Theseare to be not less than lf in. apart, andmust be placed so that the plug of oneis opposite the socket of the other.

Improving Tuning.There are at present on the market

specially constructed double -coil holdershaving interchangeable plugs and sockets,and these can be recommended for thepurpose. An additional variable condenserwill be required for reaction control, andthis is another component that has beenspecially developed ; if the set is slightlycramped, and there is not a great deal ofpanel space for mounting a normal sizecondenser, these small reaction condenserswill, in one form or another, be found toserve quite as well.

It will be seen that a centre -tapped coilis used in the aerial circuit ; this, for quitea small outlay, will materially improve theselectivity of the set, in fact, with this orthe " X type coil, tuning is sufficientlysharp to warrant the fitting of a slow-motiondial to the A.T.C. The other coil, L3, isan H.F. choke, which may be either a specialcomponent, a large coil, for instance, one

not less than No. 250, or maybe made by the constructor.It is advisable to employ oneor other of the first two men-tioned, as an H.F. choke tobe efficient must have a lowself -capacity, and this factorreceives due considerationboth in the design of thecommercial product and intuning coils.

If it is decided to use a plug-in coil forthe purpose, mount it as far from the othercoils as possible, and, if space will allow,at right angles to them ; this will guardagainst any interaction which might other-wise occur. The foregoing remarks mustnot be taken too literally, or to mean thatthe coil is to be placed at the other endof the baseboard, as this would necessitatean unduly long lead to the coil from the

v1

plate of the detector valve, and would c omore harm than good.

When wiring up to the circuit given inFig. 2 see that the moving plates of thetwo variable condensers are connectedtogether and to earth, for by this meanstuning is more certain, as hand capacity isreduced to an almost negligible amount.The lead which is taken to the centre tapon the A.T.I. is of flex, and should be fittedwith a spade terminal to facilitate con-nection, and to prevent fraying of the end,which would mean renewing the lead aftera little use.

The R.F. Side.It will be seen that there is nothing

difficult in altering a set in which thedetector is the first valve, and to effectsimilar improvements with an H.F. stageis not much more so. In Fig. 3 is giventhe anode and reaction circuit of a straightH.F. stage with reaction on the anode coil ;the aerial circuit is not included, as thatneeds no comment, and does not im-mediately concern us.

The alterations are very similar to thosealready described for the plain detectoras far as the actual components and wiringare concerned, but with the H.F. stagethere are one or two little points whichcall for rather more attention. In thefirst place there are two H.F. chokes, onein the plate circuit of each valve, and asthis is the case there will be no room tohave plug-in coils for the purpose,


2+2 Popular Wireless, April 21st, 1928.

*MOVING WITH THE .

TIMES.(Continued from previous page.)

The two-way coil holder is replaced bytwo fixed coil holders, and an extra con-denser is required for reaction control asbefore described. There is also a fixedcondenser (02) of .0003 mfd. capacityconnected between the plate of the H.F.valve and the tuned grid circuit, which isto prevent the H.T. short-circuiting throughthe grid coil to L.T. negative.

Transformer Coupling.A centre -tapped coil in the aerial circuit

will improve the selectivity considerably,and ensuring that the moving plates of theA.T.C. are connected to earth will minimisehand capacity ; with the alterations carriedout as suggested the moving plates of thethree condensers may be joined and earthedby one lead. As previously mentioned, theH.F. chokes should be kept away from thetuning coils, but as this time the commercialproduct must be employed, this will notcause much trouble.

If transformer coupling is used withreaction on the A.T.I. as shown in Fig. 5,there will have to be quite a re -shuffle ofthe component; to bring the set intolinewith Fig. 6. Both the two-way coilholder and the H.F. transformer will haveto be removed, the former replaced by asingle -coil holder, the latter by twomounted as described.

Two H.F. chokes are required, also the.0003 fixed condenser (04), and reactioncondenser as shown in the diagram. Thesame suggestions concerning the mountingof the coils and chokes, earthing the movingplates of the variable condensers, and soforth, are all equally applicable, and shouldbe carefully noted.

The coils for use when the alterations havebeen carried out will be as follows: inFig. 2 : L1-60 centre -tapped, L2-40-50 ;

in Fig. 4: L1-60, L2-40-60 ; in Fig. 6 :L1-60 centre -tapped, L2-60, L3-40-60.The size of the reaction coil may bo variedto obtain best results, and will depend onthe capacity of the condenser used inconjunction with it.

Another advantage would be to employ asplit -primary transformer in Fig. 5 and to usea neutralising condenser, the reaction beingaltered to conform with the type used inFig. 6, and acting on the secondary windingof the H.F. transformer. Split -secondaryneutralisation could be employed in Fig. 4if desired, the split -secondary coil, of course,being the grid coil of the H.F. valve.

" PRACTICALTELEVISION."

A book by E. T Lerner, witha foreword by J. L. Saud, hasjust been published by Ernest

Senn, Ltd., at 10s. 6d. net.

MR. LARNER rightly believes instriking whilst the iron is hot, andhis book is, on the whole, a praise-

worthy attempt to instruct the generalpublic in a subject on which there is atpresent undoubtedly more widespreadinterest, and, may it be said, optimism,than first-hand knowledge.

More than two-thirds of the letterpress isdevoted to a survey of the various systemsthat have preceded the advent of truetelevision, which the author generouslyattributes to Mr. J. L. Baird. He does,however, make casual reference to theexperiments carried out by the AmericanTelephone and Telegraph Company in theearly part of 1927, though he fails toemphasize their achievement in coveringa distance of over 20 miles by true " wire-less," or radio vision methods.

Pioneer Work.Further, he states that the apparatus

used by the American Company was amodification of that used by Mr. Baird,though it would surely be fairer to pointout that, so far as the analysing andsynthesising methods were concerned, both

are derived from a common and earlierstock of knowledge.

The earlier portions of the hook give afairly exhaustive and detailed account ofthe pioneer work done by such 'well-knownworkers in the art of still -picture trans-mission as Bain, Korn, The Bell TelephoneLaboratories, Ranger, and others.

Special chapters are devoted to theselenium cell, to the development of thephoto -electric effect, and to .the. opticaltheory of the formation of images.

In the field of television proper, or thetransmission of moving -picture effects,either by wire or through the ether, a sum-mary is given of the work carried out inthis direction by Belin, Holweck, Mihaly,Jenkins, and Alexanderson.

"Disappointing."The last chapters are devoted to a descrip-

tion of the Baird Televisor. It must besaid that they add little to descriptionsalready published in the technical press,apart from the description of a new opticallever " device, which apparently increasesthe speed of the exploring pencil of light atthe expense of light -intensity. At firstsight, this merely appears to be a questionof robbing Peter to pay Paul.

From the point of view of disclosing thelatest technical improvements in the BairdTelevisor, or of enlightening the publicas to the scientific principles whichdistinguish the Televisor from other systemsof picture transmission, Mr. Larner's bookmust, frankly, be deemed disappointing.

SEXTON O'CONNOR.

*BATTERY BREVITIES.

-410-411. *A coating of petroleum jelly or vaseline

will prevent accumulator terminals frombecoming corroded-

* * *

If your accumulator terminals are coatedwith' a green deposit, this may be removedby a solution of ordinary washing soda.

* * *

The paste inside the ordinary flash -lampbattery is highly destructive, so it shouldnot be allowed to come into contact withcarpets, etc.

) ,

/76.6

Ysdo


WHEN you go into a shop and buy aparticular valve which is rated by

' the makers as having an impedanceof, say, 20,000 ohms and an amplificationfactor of 20, you probably have a prettydefinite idea that when you put it intoyour set, no matter under what conditionsit may be working, its impedance will be20,000 ohms and its amplification willstill be 20.

There is, however, another characteristicof the valve which is known as its mutualconductance, which is merely a complicatedway of describing the slope of the gridvolts -anode current characteristic, whichhas an important influence on the function-ing of the valve. The valve is, however,one of the most variable of things, and.the only thing about it that remains any-where near constant is its amplificationfactor.

The Amplification Factor.In view of the fact that this article is

going to describe how valves vary we hadbetter take one of the most importantfactors first, that is the amplification factorof the valve, and see whether this remainsreasonably constant under varying con-ditions.

There are several different ways in whichthe amplification factor of a valve may beobtained. A simple method is shown inFig. 1, where a valve is under test.R is a potentiometer, and an alternating

current isimpressed onthe circuitas shown.The slider ofthe potentio-meter (Whichmust ofcourse havea resistancesuitable for

the purpose for which it is used) should bemoved until a point is found at which nosound is heard in the telephones.

The amplification factor of the valve willB

then be equal toA

-. In cases where nosource of A.C. is available, another formof the circuit is shown in Fig. 2. Threemeters are required for the purpose of thistest, two voltmeters and a milliammeter.

Simple Measurement Scheme.The amplification factor is obtained by

noting the change in anode current per gridvolt change and then finding what changein anode voltage has to be made in order toproduce the same change in anode current.

This then gives us the amplificationfactor, or put in another way, the changein grid volts required to produce a given

VAL

VAIZIOoNs

* II- 0 +>/c---An interesting discourse on thecharacteristics of valves which willhelp you to choose your " tubes "correctly and make the most of

every stage of your set.! By C. P. ALLINSON, A.M.I.R.E.

* - -- *change in anode current divided into thechange in anode volts which will producethe same change in anode current will givethe amplification factor of the valve.

Now what are the variable factors in thiscircuit ? The most obvious ones, of course,

are the hightension and 'grid bias,but there is athird vari-able which isthe filamentpotential oft h e valveitself. Wecan measure

the amplification factor of the valveunder all kinds of varying conditions,and we will find that there is but littlechange in its numerical value.

It has been found, indeed, that with ahigh-tension voltage as low as only 2 volts,the amplification factor obtained has beensubstantially the same as. that given when120 volts H.T. was employed. Of course,if the grid of the valve is made positive, areduction in the amplification obtainableis experienced in practice. This is, ofcourse, due to the damping introduced intothe circuits associated with the valve.

With modern dull emitters this can bevery high indeed, a positive potential of 2or 3 volts being sufficient to pass anythingup to 60 or 70 micro -amps in grid current.

What happens, how-ever, when we place aload in the plate circuitof the valve ? Thismay be an impedancesuch as the primary ofan L.F. transformer ora pair of headphonesor a resistance as usedin resistance -capacitycoupling.

In the case of animpedance, assumingthat its reactance ismuch greater than itsresistance, we shallfind that the actualamplification f actorunder working condi-tions will be slightly

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less than the theoretical amplification factorobtained by use of one of the circuits given.The difference, however, will not be great,and the amplification obtained may bebetween 90 and 95 per cent of the theoreticalfactor.

In the case of a resistanoe, however, itis by no means unusual to find that anactual amplification of only 50 or 60 percent of the theoretical amplification factorof the valve is to be obtained, thoughwhen working under the most favourableconditions it is possible to get a far higherpercentage than this, up to 80 or 85 per cent.

High Value Anode Resistances.This is one of the facts which is so highly

in favour of the use of the new and veryhigh values of anode resistances such as arefrequently used, i.e. in the neighbourhoodof 2 megohms, in that a far larger percentageof the theoretical amplification of the valveis obtainable than with the more usualvalue of resistance in the neighbourhood of100,000 ohms.

In the case of an H.F. valve, by suitablydesigningthe H.F.transformerused tocouple it tothe nextvalve we canget almostthe fullamplificationfactor of thevalve whenworking undernot usual in a receiver, however, owingto damping, stray capacity effects, strayfields and unwanted coupling of thisdescription, for us to get anything like this


ideal conditions. It is

The peculiarity of the new screened -grid H.F. valve? one of which is shownin theabove photo, is that it has a very high amplification factor, but its

impedance is also of a high order.

Popular Wireless, April 21st, 1928.

,* 4.4-0 -0-4.-4.--4-4------------*

VALVE VARIATIONS.(Con(inued from previous page.)

figure. This is not actually the fault ofthe valve, but is a defect which is inherentto any circuit and is imposed by thepractical requirements of each particularcircuit.

The two factors which generally governthe choice of a valve by a purchaser 'are

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the amplification factor and the impedance,-to say nothing of the price. This, however,is- a factor which is quite outside our'control, unfortunately. We have. briefly.considered what' happens to the ampli-.fication factor under varying conditions,let- us now see -what happens to the.impedance.

TQ talk about the impedance of a valveis not quite strictly correct, a more suitable

A point worth noting is that the physical shape or dimensions o! a valveafford no indication as to its purpose. The big valve seen above could beof an H.F. type and capable of handling but small inputs, while one of

the smaller valves might well be of the super -power class. -

and accurate term of description being the" differential A.C. resistance." Let usimagine, however, a conversation betweentwo wireless amateurs who are talking aboutvalve impedance and substitute the phrase

differential A.C. resistance " for " im-pedance " in each case throughout theconversation and we should soon see whata cumbersome term this is.

How " Impedance " Varies.The impedance of a valve is obtained

from the anode -volts anode -current curve,i.e. the change in anode current plottedagainst the change in anode volts.

Taking a valve which has a normalimpedance of 20,000 ohms and measuringthis at a plate voltage of about 20 volts for

instance, we shall Lind that its impedanceactually may be in the neighbourhood of25,000 or 26,000 ohms, and that as' weraise the high-tension voltage at whichwe measure the impedance of the valve wefind that the_impedance drops and dropsuntil at the normal H.T. voltage of 100, or'say 120 volts, depending on the valve whichwe are measuring, it is found that theimpedance will now come down to therated value.

Let us increase the value of H.T., however,.and see what happens. Even a change of10 volts upwards shows a difference, andwhen we get up to 150 or 160 volts H.T.we find that the impedance of the valvedrops from 20,000 to perhaps 18,000 or17,000 ohms. The curve shown in Fig. 4illuStrates the variation in impedance withanode voltage in the case of a 6 -Volt powervalve.

It would therefore appear that we have aready means of altering the impedance of avalve by altering the value of the H.T.supply. Unfortunately, it is not quite sosimple as this, for, by changing the value ofH.T. we also change the slope or mutualconductance of the valve.

Effect of Grid Potential.Now the over-all efficiency of a valve is a

function of the amplification factor and theslope, and if yOu reduce the slope of a valveyou reduce its over-all efficiency, so that byreducing the H.T. applied to the anode of avalve in order to bring up its impedance wereduce, at the same time, its efficiency,because we have reduced its slope.

Fig. 3 shows a number of characteristiccurves taken at variousvalues of H.T.Although I have some-what exaggeratedwhalactually secure it willbe found in practicethat the slope of thecurve is increased asthe H.T. is increased.It will further be seenfrom this figure thatthe slope of the valvevaries with the gridpotential, especiallywhen We come on tothe curved portion oft h e characteristic,where a small varia-tion of grid voltagemakes a large differ-ence in the slope ofthe curve.

What difference doesthe grid voltage haveon the impedance of

the valve ? On making measurements wefind that it has a very important influence

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again on this already extremely variablefactor. Keeping the anode voltage fixedand starting at zero grid volts we find

:at zero gridvolts. Whenthe grid of avalve is madeeither posi-tive or nega-tive there isa slight dropin amplifica-tion factor,the greatestdrop being experienced when the gridbecomes positive.

We therefore see that under practicalworking conditions, when the grid becomespositive, not only does the amplification ofthe circuit as a whole fall off owing to thedamping introduced by the grid current,but also the amplification factor of the valveitself is reduced owing to the positivepotential on the grid.

In Detector Circuits.With the usual grid condenser and 2-

megohm leak connected to low-tensionpositive detector circuit the impedance ofthe valve may drop to a half or even athird of its rated impedance.

When, however, anode -bend rectificationis used, then the impedance of the valveincreases very greatly and may rise to avalue of two or three times the normalimpedance of the valve. This shows theimportance of choosing correct valves.

that as we make the grid more and morenegative the impedance of the valvegradually rises. If, however, we makethe grid positive, then the impedance dropsvery rapidly, but this is not a conditionunder which we work in actual practice,except in the case of the detector valvewhen using leaky grid condenser rectifica-tion. Fig. 5 shows exactly how the im-pedance of a valve varies with the gridpotential.

Filament Temperature.Another thing which affects the impe-

dance of a valve is the filament temperature,and it is found that as the filament currentis gradually reduced the impedance rapidly

rises, while111.

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how the impedance of a valve is affectedby the filament voltage.

One point which we have not yet con-sidered is the variation of the amplificationfactor of a valve with the grid potential.From tlae readings I obtained under theseconditions I found that the greatest varia-tion in the amplification factor was obtainedby varying the grid potential of the valve,but even then the variation was not morethan 10 per cent.

In Fig. 7 I have plotted the amplificationfactor of a valve against grid -bias voltage,and it will be seen curiously enough thatthe maximum amplification factor is given

negligible.Fig. 6 shows

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Build this Iwo valveamplifier with

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yOU can build a 2 -valve amplifier-to giveperfect loudspeaker results in conjunctionwith your present crystal or 1 -valve set-at

a cost of only about £1 8s. 6d. The partsrequired for a conventional 2 -valve amplifierare as under --

1 Lissen L.F. Transformer 8 61 Lissen R.C.C. Unit 4/-1 Lissen Rheostat ( 7 ohms) 262 Lissen Valveholders at 1 - each1 Lissen Fixed Condenser1 Lissen Filament Switch ----

19s. Od.1 Ebonite Panel, size about 8" x 6" x - -

1 Ebonite Terminal Strip, about 5" x 2' x -1 Baseboard (from your local joiner), 8" x 6" x - - 6d.Screws, Terminals and Wire, about - -

Total cost (except valves and batteries) - - 1 8s. 6c1.

10,000 radio dealers will sell you allthese pasts at the prices stated. Nomatter what may be specified in anycircuit or instructions you are buildingto, use Lissen parts wherever you can.Your radio dealer will also willinglytell you how to connect every circuityou are interested in if you tell himyou intend to use Lissen parts and buythem from him.

LISSEN LIMITED8-16, Friars Lane, Richmond, Surrey. (Managing Director: Thomas N. Cole.)

Zee Popular Wireless, April 21st, 1928.

tBROADCASTING TOPICS

Licence Figures Still Rising-The Regional Scheme-" Rugby-The Radio Parasite.'By THE EDITOR.* ---*

WHATEVER may be the generalopinion about the quality of theB.B.C. programmes, the number of

receiving licences issued by the Post Officecontinues to increase. According to thelatest figures the number of licences inforce has risen at the rate of over a thousanda day, and by the end of February the totalwas 2,451,051, which represents an increaseof about 33,000 as compared to the Januaryfigure. Since December, there have been95,000 new licences issued.

If we calculate at the rate of three orfour listeners for each wireless set, it willbe seen that there is a listening audiencein the country of very nearly 10,000,000.

The B.B.C., consequently, will be receivingduring the twelve months ending Marchnext a bigger grant than they receivedlast year. It is estimated that they willreceive £880,000, which exceeds the figurefor the current financial year by £75,000.These figures have been issued in theestimates of the Revenue Department.

Licence Figures Still Rising.The Post Office deducts 121 per cent

from the gross income received fromwireless licences. This 121 per cent issupposed to cover the cost of the collectionof licence fees, etc. When this has beendone, the B.B.C. receive 90 per cent of thebalance as regards the first million licences,80 per cent of the second, and 70 per centof the third million.

All this points to a steady increase in thepopularity of broadcasting, and it iscertainly a very good answer to thosecritics who maintain that the B.B.C. islosing ground, and that interest in broad-casting is waning. It has been suggested,however, that as there have been more thana thousand prosecutions of listeners whohave failed to take out licences, this has hadthe effect of making many pirates come toheel as regards paying their licence fees.There may be something in this, but it isdoubtful whether it really explains thefact that licences during the last threemonths have shown a rise at the rate ofover a thousand a day.

Renewed inquiries at the B.B.C. withregard to the Regional Scheme have againbeen met with the reply that the PostOffice has not yet given permission for thescheme to be proceeded with. It is now twoor three years since the Regional Schemewas first suggested, and the general im-pression, as has been pointed out in thesecolumns before, is that although the schemeis very fine on paper, it does not seem tolend itself to practical fulfilment.

The Regional Scheme.

Anyway, the only definite sign is 5 G B,and listeners are wondering more and morewhether the full Regional Scheme is everlikely to mature. It must be admitted thatthe B.B.C. has strained every nerve in thisdirection, but for some reason or other thePost Office seems to be more than usuallyslow in the matter.

It was suggested the other day that as thePost Office station at Rugby is certainlynot paying its way, some sort of an arrange-ment might be arrived at with the autho-rities for Rugby to devote, part of its timeto broadcasting. It is interesting to note,by the way, that POPULAR WIRELESS,some tithe ago now, published an articleentitled : " Rugby, The Radio Parasite,"suggesting that even before the stationwas completed it would be out of date,for the modern trend in transmission designwas in the direction of short-wave beamstations.

Rugby-The Radio Parasite.Rugby, these days, seems to be making

more use of short waves on low power.The station is capable of utilising a powerof something like 800 kilowatts, but despitethe inauguration of transatlantic telephoneservices and the transmission of officialPress bulletins, etc., there is no doubt thatRugby is not being overworked; and thatwhen it does transmit it makes more andmore use of short waves, as any listenercan test for himself if he listens in on theshort waves when Rugby is transmitting.

Rugby seems to be proving itself more

impression is that a good deal of diffi-culty exists in producing complete freedomfrom hum. Never having had< trouble inthis direction myself, I find it difficult togive advice on the subject. As a generalrule, however, I certainly say thatthere should be no need to go to suchextremes as screening the set or earthing thevalve bases. Probably the golden rule isto keep the leads in the detector circuitas short as possible, and to keep the coilswell away from any house wiring or trans-formers in use on the eliminator.

Semi -Vertical Aerials.A semi -vertical aerial that I have in use

at present seems to be giving excellentresults on really long-distance stations.By arranging an inverted Li type, I canobtain a length of over 100 ft., but theavailable 70 ft. of 1' semi -vertical," i.e.straight up from the window .to the top ofthe mast, gives better results altogether,both from reception and transmission pointsof view. Probably location has a good dealto do with it.

Incidentally, those who are situated nearmain roads now find trouble arising on23 metres that was never experienced on45 and 90 metres. I am, of course, referringto bus and car magnetos. Not until a fewdays back did I realise what an appallingclatter exists in such localities ! A friendfinds it practically impossible to receive2 X A D on 21 metres for more than tenconsecutive minutes, or even less, on ac-count of this tiouble. It is difficult indeedto suggest a remedy in cases like this, otherthan screening the whole set in a copper

box and earthing it.Even this does not

One of the features of the new wireless station which serves the CroydonAerodrome is a very complete and efficient earthing system. The connectingwires shown in the above photo are, joined to a large buried earth ring

which surrounds thei station.

and more a white elephant, for, despite arecent reduction in the, transatlantic tele-phone charges, it is still very much under -worked in this direction.

'SHORT-WAVENOTES.By W. L. S.

*-÷-...-.....--------.-4-4.---.*MY recent notes on eliminators have'

brought me some correspondence onthe subject from short-wave fans in

Various parts of the country, and the general

always produce acomplete cure;

The B.B.C.'s Chance.2 X A D, by the way,

has improved againlately, and if you havebeen neglecting your20 -metre coils, returnto them at once whileconditions are good.He sometimes comesin at 10.30 to 11 p.m.at almost unbelievablestrength, and one hasquite the impressionof listening to a power-ful local station. Nofading is noticed atall, and if the B.B.C.ever had an oppor-tunity of a reallyimpressive relay, itis here now.

Ten Metres.The " ultra -super -short waves " are now

undergoing startling developments. Notuntil this year has transatlantic workbeen carried out on 10 metres, but it hasnow been accomplished four or fivetimes, and the 10 -metre wave, after theinitial trouble in getting down t he -r e,seems fairly -consistent. I am not forecast-ing the growth of broadcasting stationson 10 metres ; but, after all, the wholespectrum of short wave -lengths has beenbrought into use very slowly, and " abit at' a time," and there is no possiblereason why the 10 -metre band should notultimately prove the pick of the wholeband.


Cathedral choristers with selected voices-from some famousedifice-let them sing to you. Let their voices come to youclear and loud. For this you must have smoothness of currentfor your valves, and nothing is smoother than the current of aLissen battery. There is no ripple in it, there is no noise. It isfree from hum. It yields power in abundance, and the powerlasts. For there is a new process and new chemical combinationembodied in the Lissen battery which is known only to Lissen.The big cells of this battery have a remarkably large oxygencontent which keeps the current flow steady throughout thelongest programme and sustained throughout months andmonths of use. And your loud speaker utterance remainsnatural and true all the time.For economical power, for good power, for the best kind ofpower, for radio use a Lissen battery. You can buy it fromany one of 10,000 radio dealers. Ask for a Lissen and showplainly by the way you ask that you mean to take no other.6o volts (reads 66v.) ..7/11roo volts (reads 'ay.) .. 12.116o volts (super power)..9 volts (Grid Bias) .. 11641 volt Pocket Battery .. , 5d.

LISSEN LIMITED, 8-16, Friars Lane,Richmond, Surrey.(Managing Director :

Thos. N. Cole.)


All Editorial Communications to be addressed to The Editor, POPULARWIRELESS, Tallis House, Tallis Street, London, E.C.4.

The Editor will be pleased to consider articles andphotographs dealing with all subjects appertaining towireless work. The Editor cannot accept responsibilityfor manuscripts and photos. Every care will be takento return MSS. not accepted for publication. A stampedand addressed envelope must be sent with every article.All inquiries concerning advertising rates, etc., to beaddressed to the Sole Agents, Messrs. John 11. Lile,Ltd., 4, Ludgate Circus. London E.C.4.

The constructional articles which appear from timeto time in this journal are the outcome of research andexperimental work, carried out with a view to improvingthe technique of wireless receivers. As much of theinformation given in the columns of this paper concernsthe most recent developments in the radio world, someof the arrangements and specialities described may bethe subject of Letters Pa.ent, and the amateur and thetrader would be well advised to obtain permission ofthe patentees to use the patents before doing so.

QUESTIONS ANDANSWERS.

DISTORTION.R. C. C'. (Accrington, Lanes).-" I -have

heard a lot about distortion, and I haveheard plenty of it, goodness knows. Butalthough there are plenty of high -brow ex-planations, such as H.F. leakage in L.F.circuits, and so on, there seems to. be verylittle practical information as to where one isto look for distortion in a set. I mean tosay, is it the grid leak, or is it the coil, orwhat 1 "

The following are the Commonest causes of dis-tortion

(a) Too much reaction, i.e. reaction sail with toomany turns of wire, or reaction condenser of toohigh a capacity.

(b) One or more of the batteries running down.(e) The use of unsuitable valves, such as a de-

tector valve used for the last stage, in a loud -speakerset.

(d) Incorrect voltages of either the MT., L.T., orgrid -bias batteries.

(e) The use of a grid leak of unsuitable value.In addition. sets which employ neutrodyne con-

densers are often guilty of distortion if the setting ofthe condenser is not accurate.

SHORT-WAVE ABBREVIATIONS." OLD SOLDIER (Coventry, Warwickshire).

--" What I did in the Great War, daddy, wasto sit underground, and take short messages froman aeroplane which was spotting for a gunbattery ! And being able to read Morse Inow get as much fun out of short-waveamateur signals and other Morse signallingas I do out of broadcasting. I am trying tolearn all the abbreviations, and although Ihave a list (starting with QRA-What isthe name of your station,' etc.), there areseveral signals for which I am unable to finda meaning. Can you tell me, for instance,what QSSS means, and QSS ? "

By common consent the letters QSS mean " fadingsignals." So if they are followed by a query itmeans " Are my signals fading ? " And the groupQSS without a query means your signals arefading?' QSSS means "Are my signals swinging ? "whilst QSSS without a query means "Tour signalsare swinginf."

HOW DOES THE VALVE WORK ?S. G. (Biggleswade, Beds.).-" What makes

the valve work ?. Why do we always connect.an aerial to it, and why do we tune between

ik

re= P.W." TECHNICALI QUERY DEPARTMENT

Is Four Set "Going Good " ?Perhaps some mysterious noise hasappeared andis spoiling your radioreception ?-Or one of the batteriesseems,to run down much faster thanformerly I-Or you want a Blue Print ?Whatever your radio problem may be,remember that the Technical QueryDepartment is thoroughly equipped toassist our readers, and offers an unrivalledservice.

Full details, including a revised scale ofcharges, can be obtained direct fromthe Technical Query Dept., " PopularWireless," Tallis House, Tanis Street,London, E.C.4.

A postcard will do : On receipt of this anApplication Form will be sent to youfree and post free, immediately. Thisapplication will place you under noobligation whatever, but having theform you will know exactly what in-formation we require to have before usin order to solve your problems.

--5111/111I11111111111111fill11111111111111111111111111111111Mill:1111111111171

grid and filament with the coil and condenser ?In fact, what does really happen inside a.valve ? "

You have raised some very big questions here.S. G., and althotagh it is impassible to reply at allfully, we hope that the senompaitying diagram willhelp to make clear the 'operation of a valve. In thedimsnum the essential wets of a tuning circuit andthe electrodes of a valve are shown, and no doubtyou will recognise these quite readily : only theessential connections are shown.

To understand how the valve works we mustimagine that its filament is glowing. and that particlesof negative electricity (called electrons) are con-stantly /eating the filament and flying across thevalve to the plate. TO do this thkc have to passthe grid. Many millions of electrons are making thisjourney when the valve is in operation.

This steady current is made to pass through thetelephones, and if the aerial and tuning circuits areproperly connected to the valve, the current flowing

through the telephones will be so modified that it willreproduce the -broadcasting which is being tuned in.

How this happens can be understood when it isrealised that the grid is placed in a strategic positionto intercept the current that is Sowing from filament

10 plate, and to modify or alter its volume. (SeeFig. I.) When we connect up the H.T. battery wemake the filament of the valve negative and the plateof the valve positive.

Voltage Variations.If we leave the grid circuit unconnected it will

exercise practically no effect on the stream flowingbetween negative and positive across the valve ;but if we charge the grid with electricity it will havea very marked effect upon the current stream flossingacross here. Probably you remember that negativerepels negative and that positive repels positive. If,therefore, we make a grid negative enough it willrepel all the negatives from the filament and forcethem lack, so that they cannot pass over to theplate terminal at all, and thus we shall cut off thesupply to the telephones. If we make the grid a littlenegative, we should cut off the supply to a smalldegree, and if we impart constant small charges tothe grid we should constantly modify the platecurrent accordingly.

Now, when a timed circuit is connected, as shownin the diagram between the filament and grid ofthe valve, current flowing in the aerial -earth circuitwill set up voltages across this; portion of the circuit,and these voltages will vary exactly as the currentsflowing in the aerial vary. In other words, the etherwaves flowing in the aerial will tend to producevoltage variations between grid and filament ofthe valve.

Now, voltage variations between grid and filamentof the valve result in current variations betweenfilament and the plate of the valve (that is to say,plate variations in the telephone circuit), and it isthese plate current variations in the telephone circuitthat operate the telephones by causing corre-sponding magnetic impulses that pull and push thediaphragm in such a way, and with such a frequencythat the speech -frequency, which was a characteristicof the received wave, is reproduced in the telephones.

There are, of course, many other aspects whichaffect reception, but this is a very brief statement ofthe reason underlying the various connections tothe valve.

THE HUMMING BIRD.E. J. T. (Richmond, Surrey).-" When I

bought it, my idea was to get a sort of MelodyMaker' ; instead of that I got a humming bird.It is powerful all right, and I can hear theprogrammes all right-but, oh boy, the hum !As soon as I switch on there is a hum and adrone like ten thousand aeroplane engines:

"I called in a friend who thinks he knouts alot about wireless, but I have come to the e.m-elusion that he does not know so much as Ithought he did, for all he could suggest wasthat it was the electric light ! The set hummedand hummed, and my friend hummed andha-ed, and altogether I am fed up to the teethwith it-and him, too! Do you think it is theelectric light, and, if so, can you tell why itstill goes on when all the lights are switchedoff ? And can you suggest how I can makethis humming bird into a proper songster thatwill snake a noise that is worth listening to ? "

You can soon find out whether it is something inthe set itself or in the position of it, because if the setis all right it would work O.K. on another aerialwhere good results are being enjoyed at present Whynol the it on your friend's aerial and earth to decidethis point ?

If it works well there-and we expect it will-Weaspect the you can make it work well at home, too,by a little attention to the aerial and earth connec-tions. Possibly, as at present arranged, your lead-incomes close to some of the electric wiring in the house.



RADIOTORIALQUESTIONS AND ANSWERS

(Continued front previous page)

Or, if the lead-in is O.K., perhaps the earth wire, onits journey to the earth terminal or to the hintedearth or water tap, passes close to the house wiring.

You must keep these wires-indeed, all the wiresto and from the set-as far as possible from theelectric light wiring, remembering that the latter maybe concealed in the walls of the house. We should,first of all, disconnect the aerial and see if the hum-ming is just as bad. If so, probably the earth leadis to blame. Test this by reconnecting the aerialand disconnecting the earth lead ; and, finally, youcould shift the set itself to see what effect this madeupon the humming. In this way you should soonbe able to trace where the interference is coming from,and by rearranging the wire suitably you shouldcompletely overcome it.

THE " ALL -PROGRAMME " THREE.L.S. Reading (Berks). "I am going to build the

`All -Programme' Three, which was recentlydescribed in P.W.' What 6 -volt valvesshould I use for it ? "

For the first and second valve sockets you shouldhave valves of fairly high impedance and high -amplification factor. For these positions valveswith an impedance of, say, 30,000 ohms are O.K.,the second valve having a slight negative grid biasof, say, 1§ or 3 volts. For the last stage you willrequire a super -power valve or, at least, a good powervalve, several good examples of the former beingobtainable in the 6 -volt class.

CALCULATING FILAMENT RESISTANCEVALUES.

" CAPACITY CHARLIE " (Rugby, Warwick-shire).-" I have a 6 -volt accumulator, andI want to use 2 -volt valves with it. How canI calculate what should be the value of theresistance in series with the 2 -volt valves ? Imust know this because the last valve in theset is a 6 -volt power valve, and I have not a2 -volt valve of this class; but I have severalvariable rheostats on hand which I could

insert into the leads of the valves in which Iwant to use 2-volters. What I am puzzledabout is to know how many ohms to put inthem. Can you tell ma, so that I can work itout for various valves ?

In such a case the resistance of the rheostat, or ofthe fixed resistor, which is necessary with a valvethat should be run from a lower voltage than thatof the accumulator, can easily be calculated by aslight modification of the ordinary Ohms lawformula.

Ohms law says that if the volts are divided by thecurrent in amperes, the answer will be the resistancein ohms ; in other words,

V

c.If we call the correct consumption of the 2 -volt

valve C, and if we subtract the voltage at whichthe 2 -volt valve should operate from the voltage ofthe accumulator and call this figure B, then therequired resistance R in ohms will be equivalent toE divided by C. For instance, supposing that weare going to use a 6 -volt accumulator with a valvewhich is rated to take -25 ampere filament currentat 1.8 volts, we can use the above formula as follows :

To determine E we take 1.8 volts from 6 volts, andthe answer is 4.2 volts. This gives us B, and C is therated current consumption of the valve-i.e. 25amperes. To find R we divide C into B and, in thiscase, the answer is 16-8.

In other words, if a 6 -volt accumulator is to beemployed instead of 1.8 volts, an additional resistanceof 16.8 ohms will be necessary in the circuit. Anyother resistances can be worked out in the samemanner.

TELEVISION.E. J. (Leytonstone).-" I want a real good

television set. Where can I get one ? "We rather suspect you are trying to pull our leg,

B. J. ; but, in any case, real television sets are notyet available to the public. If they were available,their cost would be absolutely prohibitive. And,finally, there is no immediate prospect of a televisionservice starting, so that, even if you got the set,there is nothing to see I

OSCILLATION WITHOUT HOWLING.M. L. (Amersham Common, Bucks).-" It

is a two -valve set. And my neighbour corn-pldins that when I switch it on I take away

all his reception. And he says I can be prose-cuted for oscillating. But my set does nothowl at all, and, once it is switched on, I leaveit alone. And never 'readjust it until the endof the performance, when I switch it off again.Is it possible for the set to oscillate withoutmy being aware of it ? "

It is possible for the set to oscillate without itmaking this condition known to its owner by meansof howls or squeals, as an oscillating set often onlysqueals or whistles or chirps when Us tuning dial isteing adjusted.

If the tuning dial is not adjusted whilst it is oscilla-ting it is quite poss'ble that there will be no chirp.whistle, etc., but nevertheless the owner should beable to tell whether it is oscillating, because the qualityIs generally decidedly poor, speech inevitably beingindistinct, and the music being rather harsh.

If your set has a knob or handle marked " increase,"or " strengthen," or " reaction,' it is possible thatthis has become knocked out of position, andconsequently the set is oscillating all the timethe set is in use and upsetting your neighbour'sreception.

On the other hand, it is quite possible for a setwhich is not oscillating to have a marked effect upona neighbour's receiver if the two aerials happen to runvery close to one another. Even sets which cannotpossibly oscillate, such as crystal sets, can have amarked effect upon one another in this way, owingto interaction across the space between the twoaerials.

The only -remedy is to increase this space as far aspossible. In other words, to separate the two aerials,not merely getting them the greatest distance apartbut, if possible, making one cross underneath orabove the other, and run at an angle to it instead ofrunning parallel with it. If the aerials must run inthe same direction, i.e. perhaps both north andsouth, it will be advantageous to have one aerialpretty high and the other pretty low, so that thedistance between them is at a maximum.

If you have a friend who has had a little experi-ence in wireless, he can easily tell you whether yourset is oscillating or not from a brief inspection of it.or you can snake a rough-and-ready test for yourself,by wetting your finger and tapping the aerial terminalwith it when the set is in action.

If, then, you can hear very loud clicks corre-sponding in the telephones or loud speaker, it isprobable that you are using a little too much reactionand either oscillating or getting very neat to it ; butif the tapping is inaudible, or only just audible, you


APPARATUSTESTED

NEW OLDHAM ACCUMU-LATOR-DUAL RHEOSTATS,SIX -PIN COIL BASES-DIMMER K.C. CONDENSER,

etc., etc.

*

Traders and manufacturers are invited to submit wireless sets and components to the " P.W."Technical Department for test. All tests are carried out with strict impartiality in the " PW."testing -room, under the supervision of the Technical Editor, and the general reader is asked tonote that this weekly article is also intended to provide a reliable and unbiased guide as to whatto buy and what to avoid.-EDITOR.

NEW OLDHAM ACCUMULATOR.T T is owing to the fact that the modern1 valve is of such an economical nature

that there is always a possibility that theaverage accumulator does not receive thecare and attention it needs. A three -valvereceiver may require only .3 amp. L.T.,and elementary arithmetic shows thatwith a battery having an ampere -hourcapacity of 30, some 100 hours or so ofrunning can be attained before re -charging

becomes essential. But most accumulatorsneed to be attended to at least once amonth if their lives are to be usefully long.

The Oldham people have, however,produced an accumulator specially suitablefor slow discharge work, but which can bequickly charged. It, therefore, fulfilsmodern requirements and is just thebattery the average listener having a threeor more valve set, using modern dull -emitters, needs.

This new Oldham is known as theU. V. D., and is of a particularly robustcharacter. Of paramount importance inits design are the strong laminated plates-a feature which did much to enhance thepopularity of the original and smallerOldham slow -discharge cell. Also, it hasa thick glass case, an item which will appeaito the amateur who has had trouble withthe celluloid distortion, cracking, andconsequent leakage which occurs with someof the cheaper cells cased in this materia:after but a few months of service.

The Oldham people have also produceda patent skeleton type of carrier for theirnew cell. This fits under a moulded shoulde*in the glass case of the battery. It can befitted or removed very readily, and cannotpossibly become misplaced. The use ofthis carrier eliminates one more accumulatorsnag-i.e. that of carrying it with some-thing which acid will not readily destroy.

Messrs. Oldham have solved a number ofincidental battery problems with theintroduction of the above deVices, and wefeel sure readers will accord these items ahearty welcome. The U. V. D. cell is ratheflarge for its capacity, but in view of itsrobustness it can be forgiven for that.

DUAL RHEOSTATS.The Burndept Wireless, Ltd., recently

sent us one of their Dual Rheostats amione of their Super -dual Rheostats. Theformer provides the ranges of zero to ,5

and zero to 30 ohms, and the latter zeroto 10 and zero to 60 ohms. The generaldesign of both these components is thesame, and their prices are 5s. each. Each is


300

- APPARATUS TESTED.(Continued from previous page.)

*

supplied complete with aluminium scaleand polished black bakolite pointer knob.

We notice that the two resistance rangeson each rheostat are styled " dull " and" bright," words which will have littlesignificance to the modern listener nowthat the old bright emitter is, to all intentsand purposes, obsolete. These Burndeptrheostats are designed for single -hole panelmounting and are well -made. Their actionsare smooth, although definitely positivethroughout the whole range of movement.

It is interesting to note that the Burndeptpeople supply high -resistance rheostatswhich can also be used as potentiometers.At 5s. there is one having a resistance of250 ohms which will carry 15 amp.Another of these potentiometer -rheostats isstated to be the highest wire -woundvariable resistance made. It has a resistanceof 2,000 ohms, and can carry 50 milliamps.It is mainly intended as an eliminatorvoltage control. Its price is 7s.

A CORRECTION.In an advertisement which appeared in

our issue of April 7th (page 236) concerningthe 4 -electrode valves manufactured byAneloy Products, 36, Hindman's Road,E. Dulwich, London, S.E.22, a printer'serror occurred. The first sentence in thebody of the advertisement should haveread :-" The wonderful new valves for

your set, which only require half the usualH.T. yet give better selectivity and purerreproduction."

SIX -PIN COIL BASES.We recently received samples of new

coil bases from Messrs. Cason Mouldings.They each measure 2a in. by 21 in., andhave the standard arrangement of sockets.Terminals and soldering tags are supplied,and the contacts are sunk in order torender it impossible for the coil to shortthe H.T. by inserting it incorrectly. Anovel feature is that the contacts are inthe form of phosphor -bronze coil springs,these being extended underneath thebase to form continuous contact to theterminals. The base is a very clean mouldingand its insulation quality high. Theprice of this new Cason six -pin coil baseis ls. 6c1., and it appears to us to becheap.

SPRING CLIPS.We recently published a photograph of a

group of spring clips. This accompaniedan article dealing with the uses of theselittle accessories. In drawing attentionto the fact that the majority of the springclips illustrated are of foreign manufactureMessrs. Ward & Goldstone, Ltd., of Man-chester, submit three samples of theirown British -made clips. Two of theseare of large size, and are lead -covered.These are accumulator battery -chargingclips which greatly facilitate battery -boardconnections at charging stations. Thesmaller sizes are brightly nickelled, andcan be used for coil tapping connections,and the- other purposes indicated in the


above -mentioned article. These Goltoneclips are very well made and quite cheap,and we are sure readers will give thempreference to those of foreign manufacture.

THE "HOBBIES THREE."Messrs. Hobbies, Ltd., of Dereham,

Norfolk, recently sent us full particularsof the " Hobbies Three," an attractivedesign recently introduced by them. Itappears to be a good, straightforwarddetector, and two low -frequency set, hav-ing the attractive feature that it willtune to both the ordinary and the longwaves without coil changes. The fulldescription of this set is contained inthe March issue of " Hobbies."

DUBILIER K. C. CONDENSER.Through an oversight in the Printing

Department a paragraph was omitted fromthe Dubilier page advertisement whichappeared in our April 7th issue.

The paragraph, one which emphasised.the advantages of the DUBILIER K.C.CONDENSER, was as follows :

" How delightful to be always certainof your station-to be able to tune inwhatever station you desire with no timewasted in undecided searching."

This component undoubtedly fulfils allthat the makers claim for it, and is excellentvalue for money. At 12s. it is supplied com-plete with a large knob and nicely engraved4 -in. dial. The vanes are of hard brass,and the whole structure of the componentreflects excellent design and finish. Theslow-motion drive is as good as any wehave examined in any condenser of anyprice.

MAKE YOUR OWN CONE SPEAKERAs described by the TechnicalStaff of "The Wireless Magazine" Using the

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302 Popular Wireless, April '21st, 1928.

RADIOTORIALQUESTIONS AND ANSWERS..

(Continued from page 299.)

can be pretty sure that your set is not oscillating andthat any interference it is causing is due to the factthat the aerials are too close together. -

THE CAPACITY OF AN ACCUMULATOR.S. ,P R. ,(Harle,sden, London, N.W.).-

" What is meant by the capacity of an accu-mulator '? ". The capacity of an accumulator has nothing what-

ever to do with " capacity " in the sense that we usethe, term applied to condensers. What is meant is theaccumulator's capacity to give sip a certain amountof electricity.

An accumulator is designed to produce 'a certaincurrent, and this is reckoned in amperes ; and it willgive this current for a certain time, which is reckonedin hours. The product of these two factors is calledthe " ampere -hour -capacity " of that accumulator.

For instance, if the actual capacity of an accumu-lator is 40 ampere hours, it means that this accumu-later will give 1 ampere of current for 40 hours.Similarly it would give half an ampere for approxi-mately 80 hours, or it would give 2 amperes for 20hours, before recharging became necessary.

So we see that the ampere -hour capacity of anaccumulator can be regarded as a convenient methodof finding how long it would last if it gives a certaincurrent, or conversely how many hours it will take todischarge it,lf the discharge is at a certain rate.

A good idea of the number of hours an accumu-lator will last without recharging can be obtainedmerely by adding together the current consumptionof all the valves in the set ; then divide this figure.into the actual ampere -hour capacity of the accumu-lator and the answer will be the number of hours thatit will last (approximately). It is important to notethat this applies to the actual ampere -hour capacityof the accumulator and not to the ignition " rating,which is generally about twice that of the actualampere -hour capacity.

THE " COSSOR MELODY MAKER."P. W. D. (Wantage, Herts).-" Where can

I obtain the issue of MODERN WIRELESSdescribing how to operate the 'Cossor MelodyMaker' ?"

The article In question appeared in the Marchissue of " Modern Wireless." and back numbers of thisjournal (and of " The Wireless Constructor " andPOPULAR WIRELESS), can be obtained from the BackNumber Department, Amalgamated Press, Ltd., BearAlley, Farringdon Street, London, E.C.4.

THE " ANTIPODES ADAPTOR.".F. H. J. (Abertillery, Mon.).-" I hitve

read the article called'' The " Antipodes Adap-tor " ' in P. W. ' No. 303, and t would verymuch like to make this adaptor, for as ithappens, r have most of the components on

CRYSTAL AND 1 L.P.

The correct connections for a Crystal and1 L.F. receiver are shown above.

In last week's " What is Wrong ? " diagramthe transformer windings were reversed, andthe crystal was not placed (with the trans-former) across the oscillatory circuit ; another" error " was made in the grid -bias connec-tions, which were shown reversed.

hand. The set that I now have is a 'CossorMelody Maker,' so would you mind telling meif the 'Antipodes Adaptor' would work allright with this ? "

The " Antipodes_Adaptor " is designed for use withone ordinary -set, provided it has one or more low -frequency amplifying stages: In your case, the setnamed has one detector and two L:F. stages, so it isperfectly O.K. to use -the adaptor with this.

All that you have to- dais to plug the " Antipodes-Adaptor " into the detector valve-that is to say thefirst valve, in this particular set. For the benefit ofother readers who would like to make up the " Anti-

- podeS Adaptor," it may be as well to explain that this- easily -constructed gadget is readily plugged into the detector -valve socket on ally ordinary set enabling itto tune on the shorter waves and even to pick upAustralia direct. . ,

it is important to note that the " Antipodes Adap-tor " plugs into the detector valve so that the signalswhich it picks up -are detected in the ordinary way,and then amplified by the flow -frequency stages ofthe set. The fact that in certain sets there may behigh -frequency valves in front of the detector isquite hmnaterial. and will not affect the operation ofthe " Antipodes Adaptor" in any way. All you haveto do with it is to plug it into the detector stageof the set and listen to the short-wave programmeson the loud speaker.

CORRECT GRID BIAS." RULE OF THUMB " (Market Harborough,

Leicester).-" Some time ago in P.W. ' I re-member seeing a rule for the calculation ofgrid bias. It had something to do with theamplification of the valve if I rememberrightly, and as it is impossible to rememberthe correct grid bias for all the different valvesone mimes across, I should be very glad if youwould tell me what this rule is."

Although the rule does not pretend to be abso-lutely accurate, It will serve as a useful guide inapplying an approximately correct grid -Maw voltage.to any valve. The rule is to multiply the amplifica-tion factor of the valve by 2, and divide this figureinto the high-tension voltage required by the par-ticular valve.

Suppose, for instance, that a valve which happensto have an amplification factor of 8 is being used,


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303

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mmisoismommmimmIN RADIOTORIAL NEWS FROM SAVOY HILL.HIGH TENSION QUESTIONS AND ANSWERS (Continued from page 288.)

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and it is required to find how much grid bias shouldbe given when 180 volts are applied 'to the plate ofthe valve. The rule given above says that twicethe amplification factor (equals 18), divided intothe high-tension voltage 160 gives the answer 10.This then is approximately the grid -bias voltagerequired by a valve having these characteristics.

THE EFFECT OF DAYLIGHT.F. T. (Watlington, Oxon).-" I built the

set in February thinking I should be ableto hear the B.B.C. programmes only. To myastonishment I have listened in to stationafter station on the Continent, and everyevening since I have put the set up T havehad hours and hours of enjoyment from it.

" But this is what is puzzling me. One ofthe very first foreign stations that I got on theset was at 5 o'clock in the afternoon, andjust at first I could count on one or moreforeign stations round about tea -time. Butjust lately I have had to wait till 7 o'clockbefore I could pick up anything at all worthlistening to from the Continent, and it nowseems as though reception only gets betterand better as the hour gets later and later.Why cannot I receive in the early evening likeI used to ''

Long-distance wireless reception Is never so goodin daylight as it is in darkness, and for this reason,the winter evenings are far better for receiving long-distance programmes than the summer evenings. Itis because the days are lengthening that you havebeen getting out of touch with the continentalstations until a comparatively late hour.

You will find that during the summer eveningsit may be as late as half -past nine before you are ableto get a continental station, but as soon as theautumn days come round again and the darknesssets in earlier you will be able to pick up the continen-nental stations early in the evening once more.

HIGH-TENSION VOLTAGE.S. E. B. (Bolton, Yorks).-" The power

valve is marked 60 to 120 volts for platevoltage, and what I would like to know is willit go just as well on 60 as it will 120, and ifso, why use 120 ? If it will not, why give' 60' as a voltage when it only works pro-perly at 120 ? "

It is always an advantage to give the valve thefull plate voltage which it is capable of standing-in case 120 volts. If this voltage is appliedwith the correct grid bias, better reproduction willbe obtained than when 60 volts Is applied, eventhough the grid bias is altered accordingly.

The reason that the two voltages are given insteadof only the maximum voltage is simply a questionof 2.s.d. It is not everybody who can afford topay for a 120 -volt battery so as to get the bestpossible reproduction, so the manufacturers of thevalve give the lower figure as well to show that thebattery may be as low as 60 volts and still get reason-ably good results.

Anything below the lower figure will give un-satisfactory results, and anything above 120 voltswill tend to shorten the life of the valve. So that thegolden rule is to use the maximum .plate voltageas given by the makers of the valve H possible. and ifthis cannot be done to get as near that figure ascircumstances permit.

GRAMOPHONE PICK-UPS." COLUMBIA " (Enfield Town).-" The gra-

mophone is an old timer, but I kept it becauseit is portable and could be relied on to kickup plenty of noise. I am wondering whetherit is advisable to get a pick-up for use with it,because it is an old instrument and the qualityit gives does not compare with my wireless -set. Would the fact that it is a boxed -inportable be against it ? "

With the gramophone pick-up the most importanpart of the reproduction is done by the wireless set,and if you have a good set you can rely upon reallygood gramophone -radio reproduction. All that youneed from the gramophone is a good motor with noobvious mechanical weakness. If the gramophonewill take care of the turning of the record all right,you can be sure that the pick-up and the wireless setwill take care of the programmes. We Shouldcertainly buy a pick-np in the circumstances, and weexpect that you will be more than satisfied both withthe volume and the quality

therefore.,with more prospects of successthan formerly, when the initiative was withthe B.B.C. Indeed, there seems to bequite a good chance of the scheme maturingin time for next season's, business. Mr.Lynes, of Graham Amplion, Ltd., is amoving spirit.

Regional Delays.There is undoubtedly extreme tension

between the Post Office and the B.B.C. onthe subject of the Regional Scheme. ThePost Office makes Fabius Maximus Cunc-tator look.like a sure Derby winner. Butstill the B.B.C. declines to break cover, andtake the public fully inte its confidence. Ifthe deadlock is unrelieved for anothermonth or so, it will be too late for the B.B.C.to escape sharing the censure that willdescend on the Post Office. It is high timethat there was some frank publicity aboutthe Regional Scheme.

" Machines."Highly interesting developments - are

expected in connection with the final rejec-tion by the B.B.C. of the play which CaptainReginald Berkeley was specially com-missioned to write and which was rejectedthe first time because it was alleged to bepolitically controversial.

Sir Thomas Beecham and the B.B.C.Now that the Imperial Opera League

scheme is hiing up, speculation is revivingabout Sir Thomas Beecham's future.Despite former fulminations against radio,Sir Thomas is understood to have modifiedhis views lately. Stranger things havehappened than that 'Sir. Thomas shouldbecome a B.B.C. conductor. Such a move,if practicable, would be universallyacclaimed not only as a wise and self-sacrificing one an the part of SirThomas Beecham, but also as a triumphof reconciling statesmanship at Savoy Hill.

The Return of De Groot.Listeners will learn with satisfaction that

De Groot and the Piccadilly Hotel Orchestraare returning to the wireless programmes.It will be recalled that difficulties arosein 1926 between De Groot and the B.B.C.as a result of which his broadcasts fromthe Piccadilly Hotel ceased during Octoberof that year.

Last year he gave one broadcast, thisbeing in December, when his performancewas relayed from the Casino, Portheawl,and broadcast from the Cardiff and SwanseaStations prior to his departure on an Ameri-can tour. It is understood that negotiationsbetween the famous violinist, the PiccadillyHotel, and the B.B.C. have now reached asatisfactory conclusion and De Groot andhis Trio are giving a -Studio performancefrom London and ether Stations on Satur-day, April 28th.

" Duffy " at Plymouth.A special performance of " Duffy," a

Cornish comedy in dialect by R. MoretonNance, is to be performed by a cast of fourCornish artistes in the Plymouth Studio onFriday, May 4th. The production will besupervised by a member of the Head Officestaff and will be broadcast from Londonand other stations.


1OMEHOW you are not surprisedOwhen you first hear the richly

mellow tone of the Vrown SphinxLoud Speaker. It is because its age-old design has led you to expect it.There is something about the Sphinxthat inspires you to believe its repro-duction will not belie its proud design.You are happy, when you hear it, thatyour confidence has not been mis-placed. And if, perchance, as youlisten, you should shut your eyes, youwill be so intrigued by the reality ofits reproduction that you will have nodifficulty in imagining the artiste inyour very room. The price you payfor this living instrument is £12. 108.

Bnrndept VariableCondensers :

PRICES, withoutDial or Knob :SQUARE LAW

00007 mfds... 13/6000r . . 13/6

LOG LAW (as shown).0003 mfds. 15/-'0005 ,, . . 15/6

For the " Log -Law "Condensers, printedwave -length scales,range 550-3,000metres, can be ob-tained for use withclosed circuits.Price, 1/6 per set.

S. G. BROWN, Ltd.,Western Avenue,North Acton, London,W.3. Branches andWholesale Depot s

everywhere.

Burndept " Log -Law " Condensers-with printedwave -length scales.

'VT'Ul111111111h1

Reasons wlaYr

Azott %U.atila

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4e Condensevs1. -These Condensers are theonly type made with an insulatedspindle and a metal earth-shield-features which ensure absolutefreedom from hand -capacity andincreased signal -strength. In an" all mains " receiver the insulatedspindles remove the danger ofshocks when operating the *con-densers.2.-The construction of theseCondensers is very robust. Theadjustment is effected on thebottom end cheek by a coneseating on one side and a steelbearing on the other. The topcheek is a " steady " only-notension between end cheeks-avery fine improvement.3.-These Condensers are beingused by experts everywhere. Fitthem to your set and secure betterresults.Write for Publication No. 320,

giving full particulars.

ADJUSTABI.f 514/101.( a insuunnc rAILFinly

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2570244.6aHiptuiED

A.J W.


THE FINISHINGTOUCH

Patent

Belling -Lee Terminals are the finishingtouch to any Resolver. They are a com-bination of Beautiful Finish and FirstClass Workmanship.Belling -Lee Terminals are Bakelite insu-lated and made with 30 different en-gravings.

PRICES.Type "B" illustrated, sold in an attractive

carton carrying a year's guarantee.Price 9d. each. .

Type " M " as type " B" but non -insulated.-Price 6d. each.

Type "R" Cheap competitive insulatedEerminat with rotating name.

Price 31d. each.Illustrated catalogue fri,e on request.

TERMINALSBELLING & LEE, Ltd.. Queensway Works,

Ponders End, Middlesex.

TAYLEX WET H.T. BATTERIES.New Prices: Jars, 1/3. Sacs, 1/2. 2incs, .11d.Sample doz. (18 volts), complete with bands andelectrolyte, 4/3, post 9d. Sample unit, 6d. 15 -page booket free. Bargain list free. AMPLIFIERS :1 -valve, 19/-; 2 -valve, 30/-. 2 -valve ALL -STATIONSET, £4.-P.TAYL011,57,StudleyRd., Stockwell, London

REPAIRSAny make of L.F. Transformer, Loudspeakeror Headphones repaired and despatched within48 HOURS-TWELVE MONTHS' GUARANTEEwith each repair. 41- Post free.

Terms to Trade.TRANSFORMER REPAIR CO.,

" Repairs " Dept.,214, High Street, Colliers Wood, London, S.W.19.

7x 6,118x 6,1/410x 8,2'110x 9,2'412 x 10.3 -14X 12,4 -14x 7,2x716x 8,3'218 X 7, 3/2

Post Free.Money BackGuarantee.

Megger Test infinity Maker (2I" x 7" Panel, 3/7)

Panels rut to any size. Call, write, or 'phoneClerkenwell 7853.for quotations. Samples and prices

post free to Trade.CROXSONIA CO. (Dept. P), 10, South St., Moorgate, E.C.2Agents:-John Henry Smith, 139, Anlaby Rd., Hull;L. H. Helyar, 82, Chamberlin Rd. Norwich; A.Stredwick & Co., 27, The Mkt., Chatham; Boynton

& Co., Ltd., 34, Bradford St., Bliant.

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ThoroughlyRecommended for

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12 PLEASE be sure to mention11 "POPULAR WIRELESS." I UTI when communicating with IIIIn Advertisers. THANKS )11

EVERYTHING IRADIQ9N

WOOLLDRIDGEgIAin10 CO, LIMITED,.

IM2a LII6LE STREET.LEICESTER SCL LONDON.W.C.

TECHNICAL NOTES.(Continued from page 288.)

waves have always been easy to produce atlow power. Also very high power has forsome time been available at the longerwave -lengths. This is the first time, how:ever, that we have been able to combinethe two, so as to get relatively large poweroutputs on the short wave -lengths."

Simplified Control.A very interesting little invention, which

comes from Germany, is an electric cablecontaining two wires which are normallyinsulated from one another, but which canbe brought into electrical contact by simplypinching the cable between the fingers.This is provided for by weaving the wiresinto a loose braid, the wires being, however,separated by an elastic non-conductor.This cable has the obvious advantage thatit does away with the necessity for push-button or press -contacts at fixed points.

Abolishes Switches.Not only is the expense of providing and

installing these push -buttons avoided, butthe cable can be operated by simply grippingit at any point along its entire length. Itis found very handy for bell -ringing andsuch -like signalling, purposes, whilst forradio it is provided with a series of specialloose clips whibh may be clipped on in sucha way that they are merely retained or,alternatively, in a way to grip the cableand maintain contact between the wires.This simple device, therefore, is equivalentto a movable switch which may be operatedat any point, and it is useful for remotecontrol of radio receivers.

Are Short Waves Reliable?How reliable are short waves ? Everyone

marvels at the ease with which amateurscommunicate with fellow enthusiasts overenormous distances with almost incrediblysmall input powers. It is undeniably thrill-ing to take from the lamp -socket a powerof no more than a quarter of that requiredto heat an electric iron and to feed it intoa comparatively simple apparatus fromwhich it emerges as H.F. energy with whichwe ask a man in South Africa how theweather is there ? It is one of the marvelsof our time that two people in the quietnessand security of their homes, but separatedby thousands of miles, can interchangeideas instantaneously and so extremelyeconomically.

Skip Distances.The General Electric Company of America

have been carrying out systematic experi-ments to discover just how. reliable shortwaves are. It seems to be fairly wellestablished that 10 metres (about 30;000ke.) is about the shortest useful wave-length for most ordinary purposes. Belowabout 20 metres the waves travel betterin daylight, whilst above that wave -lengthnight time seems to be the best. Belowabout 45 metres, curious "skip distances"occur, producing regions beyond whichsignals may be heard, but within which theyare inaudible.

The General Electric experiments haveishowt.that the 32.79 metre wave is of littleuse for \,ihort distances, but a power output

(Continued on page,'308,),

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If unable to obtain send P.O. 7/6.DX COILS LTD.,LONDONI,E.8.

HEADPHONES REPAIREDTransformers 5/- Loudspeakers 4/-. All repairsremagnetised free. Tested, guaranteed and ready

for delivery in 24 hours.Discount for Trade. Clerkentvell 1795.MASON & CO., 44, East Rd., City Rd., N.1.

Cr oswound itfour bai.anded sections,giving low self.capacity, con-stant impedance,small external field.Windings fully pro.tected. Moinited onBakelite base. Greatlyimproves theCossor " MelodyMaker " when connected inplace of wire No.26. Also whenused in " 320 Express " andother circuits. write for particulars, stating requirementsfor coil drive Loud Speakers.THE WATMEL WIRELESSCO., LTD., Imperial Works,High St., EDGWARE, MIDDLX.

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"INDISPENSO"CHARGER

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11111111IIIIPIIHI1111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111111=..-- THE LOEWE RADIO COMPANY LIMITED, F.-== 4, FOUNTAYNE ROAD,= -

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CARRINGTON MANU-FACTURING CO., LTD.,Cameo Works, Sander -stead Road, South

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IN A

PORTABLE"IDEAL" MODEL.Built to accommodate any coneunit, complete with inner frame,

baseboard, lock, nickelplated fittings, etc.Oak .. .. 52'6Mahogany .. 58 -

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CABINET CRO(2DOlintsles 0623

Climax Auto -Bat Mains Components

CLIMAXSPECIALCHOKE.For H.T. Units

CLIMAXHEAVYCHOKE.For Mains Re-ceivers 21/.

CLIMAXPOTEN-TIAL.DIVIDER.20,000 ohmsor 10,000ohmswith ten tap-pings ... 5/ -

Complete listtupon applica-tion from anyradio dealer ordirect to :- A YEAR AHEADCLIMAX RADIO ELECTRIC Ltd.,Quill Works, Putney, London, S.W.15

The first home constructors' 11.T.Supply Unit was built with ClimaxAuto -Bat Components . . thefirst mains receiver was 'possibleonly with Climax products.The Climax Auto BatTransformer is double woundand carefully insulated to with-stand the high pressure of electriclight mains without risk ofdamage to the receiving set, or of.disturbance to the electric light-ing system. The Climax Auto -BatTransformer is very robust andexceptionally powerful.Two anode windings "and twofilament windings are providedfor double rectification.The overall filament voltage onload 1.9 volts, and currents upto 1.5 ampere can be obtained.The mains winding of the trans-former is tapped to suit differentmain voltages.

NEUPRICE

516EACHFrom allDealers

TRO'VERNIAThis Neutralising or BalancingCondenser is unequalled in appear-ance or performance and becauseof its wonderful efficiency, isselected for incorporation in manyreceivers, including portables.It is perfectly constructed andhas the greatest range of capacity,viz.: 2138 minfds. The controlis delightfully smooth and uniformincrease' or decrease is obtainedwith each turn of the knob. Itis dust and damp-proof and can-not short. Suitable for eitherPanel or Baseboard mounting.

GAMBRELL BROS.,76 -,Victoria St., London, S.W.I.

PLEASE MENTION "POPULAR WIRELESS"WHEN REPLYING TO ADVERTISEMENTS

H OW TO MAKE A WIRELESS GRAMOPHONEA first-class series of illustrated articles on thebuilding and installation of the very latest type ofgramophone, with electrical " pick-up " and wire-less .reception set combined, begins in " THEMODEL ENGINEER" for April 19th. Everygramophone and radio enthusiast should follow thesearticles which are full of practical hints by anexpert. " THE MODEL ENGINEER " may beordered through any newsagent, price 4d. Singlecopies, post free 5d., from the publishers

Farringdon Street, London, E.C.4.

0,e

POST ydOR C.o.O

44/4/,1%..TE!LUX:1U VIE UM S.t. ILTEST. METERMilliameter, 0-38 MilliampsVoltmeter. 0-6 and 0-120 Volts.Think of the advantage of thisinstrument. You can test yourreceiver for distortion. FindH.T. consumption. Test voltageof H.T. and L.T. Batteries.Accurate. Dependable High

Resistance.Full particulars on request.

WET H.T. BATTERY CO.,12-13, Brownie's St.,Highliolborn,

LONDON, W.0.1

TECHNICAL NOTES(Continued from page 3964

of 590 watts on 65.16 metres (4,500 kc.)will transmit commercial day -time signalsup to 100 miles.

A Radio Pioneer Honoured.Readers who take an interest in radio

doings in the United States will be familiarwith the name of Mr. Frank Cenrad, ChiefEngineer of the U.S. Westinghouse andElectric Manufacturing Company, and aworld-famous pioneer in the field of radiobroadcasting, and they will be interested toknow that Mr. Conrad has just been awardedthe Degree of Doctor of Science by theUniversity of Pittsburg.

His principal inventions relate to electricalmeasuring instruments, relay systems,current and voltage regulators, mercury -vapour rectifiers, and automobile starting,lighting and ignition appliances. Inaddition to being Chief Engineer of theWestinghouse Company since 1921, Dr.,Conrad is also a very well-known consultingengineer, and his opinion is sought on allmanner of electrical engineering problems.

Grid " Suppressors."A new series of exceptionally low -range

" metallised "'resistors is announced by theInternational Resistance Company, of Phila-delphia. The main application of theselow -value units will be as grid " suppressors"in the stabilisation of high -frequencycircuits. Lately there has been a markedinterest shown in this simple method ofstabilising the usual H.F. amplifier by theautomatic control of the feed -back action,particularly at the higher frequencies. Thismethod makes, for extreme selectivity and,minimum anode current tax upon latteries,together with more or less automaticoperation as compared with other methodsThe present receiver, using one of the olderstabilising methods making for broadtuning, may be readily equipped with thesegrid suppressors." This device is insertedbetween the grid lead and the grid terminalof the H.F. valve in each H.F. stage.

These metallised resistors are obtainablein values as low as 100 to 800 ohms andintermediate steps to meet the precise grid -suppressing requirements of all H.F. valvesand circuits.

Batteries Popular for Short Ways.Many readers may have wondered why, in

circuit -diagrams for short-wave receivers,high-tension batteries rather than H.T.eliminators are designated as a source ofplate -supply. There is a good reason forthis, as is indicated by some interesting testsmade recently.

In the first place, a short-wave receiver isalmost invariably of the regenerative type.It is designed on the low -loss principle(which, in short-wave reception, reallymeans something) and consequently isextremely sensitive and must be capable ofmaintaining the most critical adjustments.If it is used in conjunction with an elimina-tor, the unsuppressed A,C. hum, whichmight pass entirely unnoticed in the ordinarybroadcast receiver, becomes pronounced andgrows in intensity as the reaction istightened.

Furthermore, an absolutely stable anode -current supply is vital to success in short-wave reception.


THE ROLLS-ROYCE OF RADIO IS THED I X-ONEM ETER

The High Grade Radio Tester. Lour price.High value. Worth £10. Instrument, 55/-.Multipliers, 6/6 each. Radio Test Booklet. AllRadio Users need one.

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The ACONEMETER. Model VAC.3. In Case.Is a new Model measuring Alternating Current, a3 -range instrument reading 0-150 v., 0-300 v., and0-600 v. Price, inclusive of case, 75/, 1,500 voltMultipliers, 44/. extra. Get our New 72 -PageCatalogue.ELECTRADIX RADIOS,218, Upper Thames Street, E.C.4St. Paul's & Blackfriars Stations. 'Phone : City 0191.

IE THE LITTLE CELLS THAT SATISFY.Eton Primary H.T. Battery P.1. PorousPot Cells, SI and S2 Sac Cells. All complete

1 -cell 6 -cell 12 -cell 30-cetP.I 61d. .. 3/3 .. 5/9 .. 14/.S.1 6d. .. 3/. .. 5/3 .. 12/-S2 41d. .. 2/6 .. 3/10 .. 9/6Send lid. stamp for booklet giving fullparticulars to:-THE ETON GLASS BATTERY CO.,46, St. Mary's Road, LEYTON, E.10

4e' WH ITE LI E VALVE HOLDER" Mechanically and

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KAY'S CABINETSThis Cabinet, soundly constructedof Oak, and equipped with Base-board Runners, Fall Front, HingedTop, polished richdacobean, Ar 5t..for panels up to 18° wide giAlso made to accommodate any

popular set.Quotations for Specials by return.H. KAY Cabinet Manufacturer,Mount PI t Road, London, N.I

'Phone: Wel thamstow 1626.

UN I DYNE 4-EVALECTRODE

LVES

of the genuine U.C.and ThorpWe are now the sole suppliers

valves, as specially testedand recommended by the" Unidyne " inventors and Cash with" Popular Wireless." U.0.5 order.and Thorpe ICA (both 4 -electrode 591nvalves). Post free. Only direct from-UNIDYNE VALVE CO.1 CHARING CROSS, LONDON. S.W.1

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April 21st. 1.223. POPULAR WIRELESS

Stand tAle testtame

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"MELODY MAKER"Advt. Te:egraph Co.:denser Co. Ltd.. Wales -Farm Rd.. N. Acton. London. W.3.

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Permanent AccuracyVans positively spaced and rigidly braced by an ingenious locking barmafiosi give to the lgranic " Lokvane " Variable Condenser a featurepcEsmsod by no other at the pr'ce -permanent accuracy. Stationsalways come in at the same dial reading, provided the rest of the circuitremains constant.The same locking bar feature explains its remarkably reasonable price. Itenables rapid assembly while still maintaining the highest possiblestandard of precision.

The Igranic "Lo'svan?." Variable Condenseroffers mare easy. accurate tuning features than many condensers at twicethe price. List No. R.85 gives full particulars.

PRICES.moo15 mfd. . 6/6'0003 9/8'0005 10/6

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These cabinets are madein the following sizes :-No. 1. Panel, 16x 7 inches.

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Trade enquiries invited.

The MISCELLANEOUS TRADING CO. Ltd.'Phone: Hol. '894. 143, High Holborn, London, W.C.1

aV POPULAR WIRELESS April 21st. 1923

The Valve withthe wonderful1VIullard P.M.Filament improvesevery radio receiver.

THE MASTER. -VALVE

Printed and Published every Thursday hl t4., iii,p1Lliiii. iiTi. kinligaiiiateil Pres,. Ltd.; The.Fleetba-J16114`.'Fti.vrit,:!-I,Jii ,i!,I.'1,011,r,,,, E,L.4. _\ ,j.,,., n. Ii i

OiliCeS : -Mrsrs. John IT. Lile. Ltd., 4, _Ludgate Ciretei, London. E.L.4. ILigistered as a newspaper for transmisAcin_by l'aeadLin )Iagaziii, Post-. silli,11;i:H 1i:it-Inland, I7.4 per annum: 818 for six months. Abroad. 19.0 per annum, 9:9 for six months. Sole agents for South Afrii'a : Central News Aver v, L d.t s .1

for Australia and New Zealand: Messrs. Gordon d.: Goteh, Ltd.; and for Canada: The Imperial INeWs Co. (Canada), Ltd. Saturday AprI 21st, 192.It i:

popular wireless, april 21st, 1928. this year's "chitos two" re=ge)registered at the...

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