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= I INSTRUCTION BOOKLET ~ ·

FOR CONNECTiNG

H.T. ·uNITS,

TRICKLE CHARGER . & COMBINED

H.T. and L.T. CHARGER UNIT Models Nos . A.C.12, A .C.18, A .C.25, K.12, K.18,

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KEEP THIS BOOKLET FOR FUTURE REFERENCE. TRICKLE CHARGER AND " EKCO •·• H.T. UNITS,

COMBINED H.T. AND FOR A.C. AND

L.T. CHARGER UNIT. D.C. MAINS.

Notes for all Models. Only paragraphs Nos. 1, 3 and 5 apply to Trickle Charger Model T.C.1.

1. MAINS CONNECTIONS. Before connecting up any model make sure that the Unit is a suitable model for the mains supply to which it is to be con­nected. There are two types of supply, vi?. : Alternating Current (A.C.) and Direct Current (D.C.) and Model D.C. 15/25 H.T. Unit is now the only "EKCO" Unit manufactured for use on 200/250 volt Direct Current (D.C.) mains. On no account connect any of the other models to D.C. mains. Models K.12, K.18, K.25, A.C.12, A.C.18, A.C.25, and T.C.1 are for use on Alternating Current (A.C.) only and before connecting make sure that the Unit is suitable for the voltage and frequency of the mains. (These can usually be ascertained from the supply meter or by applying to the Supply Co.)

In each A.C. model two types are manufactured as follows :-1. Suitable for 200-250 volt mains 40-100 cycles or periods. 2. Suitable for 100-120 volt mains 40-100 cycles or periods.

In the base of each A.C. Model two screw sockets marked "Mains Voltage" are provided. The Insulated Connector Screw should be gently inserted and screwed into the socket corresponding to the mains voltage until tight. The unit should not be connected to the mains when this is being done. Particular attention is drawn to the fact that for the few A. C. mains which .have a frequency lower than 40 cycles or periods, special models are required.

2. For all Alternating Current (A.C.) models the earth wire should remain con­nected to the receiver as usual, but another connection should be taken from the earth terminal of the receiver or any part of the earth wire and connected to the small earth terminal on the unit. IMPORTANT. In the case of Direct Current Model D.C. 15/25 on no account must the earth wire be connected direct to the receiver (see detailed instructions for t,his Model).

3, All " EKCO " Mains-Power Radio · Devices comply with the recommend­ations of the Institute of Electrical Engineers, but certain recommendations apply to the installation of such ap~aratus. A list of these recommend­ations showing how they apply to " EKCO " UNITS is given on page 9.

4. VOLTAGE OUTPUT. It is not possible to measure the correct H.T. voltage output with an ordinary voltmeter as used for general electrical and radio measurements owing to the comparative low resistance. The resistance of a suitable instrument should be at least 1 ,000 ohms. per volt.

5. Make certain that there are no bare wires or strands projecting from the plugs or terminals of the Unit and also that there is no possibility of any connections making contact with the metal case.

. S.G. TAPPINGS. S.G. tappings are suitable only for the H .T. supply to the screen of screened grid valves and are not suitable for the supply to any other H.T. tapping unless any such tapping is fittef'with a one or two mfd. cond;:nser connected to its positive and negative terminals in the receiver.

7. If fixed condensers are connected across the H.T. terminals on home con­structed receiving sets, it is advisable to make sure that they are of good quality. Their working voltage should not be lower than 250 (test voltage 500).

8. In cases of receiving sets operating from a frame aerial, the latter should be left connected to the receiver in exactly the same manner as usual. If no earth connection is employed and it is found that the reception is marred by " hum" it is advisable to make an earth connection to the negative L.T. terminal of the Receiving Set, in the case of A.C. models and to the earth terminal" E" of the Unit in the case of Model D.C. 15/25. DO NOT connect earth wire direct to receiver or accumulator w~en using the D.C. model.

C). All models except K.25 (also 9ertain special models for A.C. mains of 25-33 cycles or periods) will fit conveniently into most portable sets in the p lace of the H.T. battery but here it is very necessary to avoid the possibility of any metallic part of the receiver coming into contact with the metal case of the Unit.

Instructions for Connecting ·<~l

Models No. A.C.I 2, A.C.I 8 &-A:cT5 H.T. Units for A.C. Mains.

OUTPUT

MODEL A.C. 12 (Suitable for receivers not requiring more ·than 12 milliamps).

S.G. Tapping-60-80 volts at up to H m.a. for screen of screened grid valves. 80 Volts. At approx. 2:m.a. 120 Volts. At approx. 9 m.a. or if intermediate tappings are not in use 120

volts at approx. 12 m.a.

MODEL A.C. 18 (Suitable for receivers not requiring more than 18 milliamps)

S.G. Tappings- H-70-85 volts at up to 1t m.a. for screen of screened grid valves.

L- 60-70 volts at up to H m.a. for screen of screened grid valves.

(If more than one screened grid valve is used it is usually necessary to use socket H.)

50/80 Volts Adjustable Tapping. Adjustable between 50 and 90 volts at up to 3 m.a. according to position of bridge (H.M. or L.).

120/150 Volt Tapping (with other tappings in use). 120 volts at approx. 14 m.a. up to 1 50 volts at approx. 9 m.a. (If the 50-80 volts tapping is not used, then 120 volts can be obtained at approx. 18 m.a. up to 150 volts at approx 13 m.a.

l,ow Output.-With mains voltage Connector Screw in base of Unit inserted into screw socket L instead of one of the mains voltage sockets, the output of socket 120/150 is reduced to approximately 100 volts at 14 m.a. up to 120 volts at approx. 10 m.a. with other tappings in use.

MODEL A.C. 25 (Suitable for receivers not requiring than 25 m.a.)

S.G. Tapping- H-80-90 volts at up to 3 m.a. for screens of screened grid valves.

M-70-80 volts at up to 1 t m.a. for screens of screened grid valves.

L-60-70 vblts at up to 1l m.a. for screen of screened grid valve.

(If more than one screened grid valve is used it is usually necessary to connect to socket H or M.)

50/80 Volts Adjustable Tapping. Adjustable in 3 stages by bridge plug between 50 and 90 volts at up to 3 m.a.

120/150 Volt Tapping (with other tappings in use). 120 volts at approx. 21 m.a. up to 150 volts at approx. 11 m.a. (or if 50-80 volts tapping is not used then approximately 120 volts at 25 m.a. up to 150 volts at 17 m.a. can be obtained).

Low Output. With the mains voltage Connector Screw in · base of Unit inserted in screw socket " L " instead of one of the mains voltage sockets the output values of the Unit are reduced to approximately the normal output of the Model A.C.18.

INSTRUCTIONS. Read " Notes for all Models " Page 1.

with especial attention to paragraphs 1 and 5. (Paragraphs 5 and 6 of the following do not apply to Model A.C.12)

\. Connect mains sockets on base of Unit as described under paragraph of " Nntes for All Models."

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2. Remove existing plugs from the H.T. wires of the Receiver and attach those provided with the Unit. Make sure good tight contact is obtained and then insert plugs into Unit output sockets to the required voltages. Important. When this operation is completed, make absolutely certain that no bare wires or strands project from the tops of the plugs, otherwise a short circuit may take place resulting in damage to Unit or Receiver.

(See-below for rliethod of connecting wires to plugs).

3. Switch on receiving set as usual.

4. Connect \)'nit to an electric supply socket and turn on the current.

5. The Receiver should now operat~ satisfactorily, but in the case""Of Models A.C.18 and A.C.25 the scree;ie'd gria H.T. plug (if used)_?Vould be tried in each of the S.G.sockets ovided ,on the Unit and leftyermanently inserted in that one giving t est result. The bridge plug_,on these models is for the purpose of a · sting the output from the 50 /8.~v6It tapping and should be tried in each the sockets H .M. and L. (Hign, Medium, Low) until the most satisfa ory results are obtained., /

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6. Low Output. (Models A.C.18 and A.C.25 only.) If ~output of the Unit appears to be too great for .th«YReceiver, disconnect Bnit from mains, then unscrew the insulated Connector~Screw from e-tfiains voltage socket in base of Unit and re-insert io/ocket " L " (see ' ow Output" above). (Socket " L" can be used irre§pective of the Ma· s Voltage. When Connector-Screw is in S(!)Cket " L" t'7"'' Mains Volt'ag# socket should be vacant.) With Unit connected for" Low Output " it is .w~ally necessllry to connect the S.G. plug toS.G.socketlt.I-:'ifused. , 'h-

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Note. It is better to switch on the valves of Receiver before switching on the current to Unit apd sw(tch off the current to Unit before switching off the Receiver.

Always disconnect Unit adaptor or plug from mains when handling the Unit or attending to the connections of thC' Receiver to prevent possibility of shod~.

Read" Don'ts , ·on Page 10.

METHOD OF CONNECTING WIR~ TO H.T. PLUGS PROVIDED WITH UNITS.

Bare the insulation from wire for approx. td only. Twist the bare end of the wire. . U nscrew the metal part of the plug from the insulated cap for aboutlu.

Push the end of the wire into the small hole at the top of the cap until the bared part is right inside. :-''1.

Screw the metal part 'fell home, a pair of pliers will facilitate the tightening.

On no account should any bare wire proj.ect from the hole in the plug.

Special Note. When inserting or removing plugs from the sockets on the Unit, it is advjsable to give the plug a slight -clockwise or right-handed twist-this will facilitate movement of the plug and at the same time prevent the . cap from be~oming unscrewed.

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Instructions for Connecting

Models K.l 2, K.l 8 & K.25 for A.C. Mains Output- Model K.12.

Model K.18.

Model K.25.

H.T. same as Model A.C.12 on page 2. L.T. Charging Current 2, 4 or 6 volts at .25 amps. H.T. same as Model A.C.18 on page 2. L.T. Charging Current 2, 4 or 6 volts at .25 amps. H .T. same as Model A.C.25 on page 2. L.T. Charging Current 2, 4 or 6 volts at .5 amps.

INSTRUCTIONS FOR CONNECTING AND OPERATING.

(Read " Notes for All 1viodels " on Page 1 with especial attention to paragraphs Nos. 1 & 5.)

l. Connect mains sockets in base of Unit as described un'der paragraph 1 of " Notes for All Models."

2. Near the " Mains Voltage" sockets in the base of the Unit are three other sockets marked " L.T. VOLTS." Insert the Insulated Connector-Screw provided into the socket corresponding to the voltage of the accumulator to be charged and screw up until tight.

3. Remove the existing H.T. connecting .plugs from the H .T. wires of the Re­ceiver and reconnect to plugs provided with the Unit. lmportant.- When this operation is completed, make absolutely certain that no bare wires or strands project from the tops of the plugs, otherwise a short circuit may take place resulting in damage to Unit or Receiver. (See Page 3 for connecting plugs to wires.)

4. The Unit may now be fitted into the compartment originally occupied by the H.T. Battery, taking great care that the metal case does not come into contact with any bare connections or other metal parts of the Receiver.

5. Connect the flexible lead marked L.T.-(ACC) to negative terminal (black or blue) of Accumulator and the flexible lead marked L.T. +(ACC) to positive terminal (red) of accumulator. The existing L.T. leads of the Receiver must also remain connected to the accumulator as usual. Make sure that these connections make good contact with the accumulator. T he charging leads must not be connected direct to the Receiver without con­nection also to the accumulator, otherwise the valves are likely to be damaged. Keep the accumulator terminals free of corrosion.

6. Insert the H.T. plugs of the Receiver into Unit sockets to required voltages. 7. Turn charger switch on top of Unit to OFF position. 8. Connect Unit to an electric supply socket and turn on the current. 9. Switch on Receiving set as usual.

10. The Receiver should now operate satisfactorily, but in the case of Models K.18 ·and K.25 the screened grid H.T. feed (if used) should be tried in each <>f the S.G. sockets provided on the Unit and left permanently inserted in that .me giving the best results. The bridge plug is for the purpose of adjusting the output from the 50/80 volt tapping and should be tried in each of the sockets H.M. and L. (High, Medium, Low) until the most satisfactory results are obtained.

11. Low Out put. (Models K.18 and K.25 only.) If the output of the Unit appears to be too great for the Receiver disconnect Unit from mains, then unscrew the insulated Connector-Screw from the mains voltages socket in base of Unit and re-insert in socket " L." With Unit connected for " Low Output" it is usually necessary to connect the S.G. plug to S.G. socket H. Always disconnect Unit adaptor or plug from mains when handling the Unit or attending to the connections of Receiver to prevent possibility of shock.

12. To charge Accumulator. When. the Receiver is not required switch off the yalves of Reciver in the usual manner and turn charger switch of Unit to " ON " position. Always adopt the following procedure in switching on and off Reciver and charging accumulator :

Switching on Receiver . . 1 Turn" L.T. CHARGER" switch td" OFF" position. · 2. Switch ?n valves (R'e'civer switch).

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Switching Off Receiver and Charging Accumulator. 1. Switch off valves. 2. Turn Charger Switch to " ON " position. Note. In some cases the additional amount of "hum" produced is very

minute when the charger switch is left switched " ON " during the operation of the Receiver. This procedure is quite permissible and has the additional advantage of trickle charging the accumulator to a certain extent whilst the receiver is in use.

Read" Don'ts" on Page 10.

CHAR.GING PERIOD.

If the Receiver is in normal daily use the charging periods for the accum­ulator should be as long as possible. In any case the actual times should be not less than those given in the following table.

CHARGING PERIOD FOR MODELS K.12 & K.18. Appr. Charging Period for each hour the receiver

Total Filament Current taken by Valves. is used. ·

Between .2 and .25 amps.

I (Example : 2 valve set using

I 1 to 1! hrs. I•'

.1 amp. valves)

Between .3 and .35 amps.

I (Example : 3 valve set using I 11 to 2 hrs.

3 .1 amp. valves) I"

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Between .4 and .45 amps. (Example : 3 valve set with 2 to 2t hrs. I 2 .1 amp. valves and 1 .25 amp. power valve)

Between .5 and .55 ainps.

I (Example : 5 valve set with

5 .1 amp. valves) I 2! to 3 hrs.

Etc., etc. I Etc., etc. I Etc., etc. I Portable Receivers usually require between .4 and .55 amps. filament cu~rent

at 2 volts and the char~ing period should therefore be between 2 and 3 hours for every hour the 'receiver is in use. If the charging switch is at the " ON " position during the time that the receiver is in use then this time may count as part of the charging period.

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CHARGING PERIOD FOR MODELS K.25 & T.C.1. Appr. Charging Period for each hourthe receiver

Total Filament Current taken by Valves. is used.

Between .2 and .25 amps.

I (Example : 2 valve set using

.1 amp. valves) I t to t hour

Between .3 and .35 amps.

I (Example : 3ialve set using

3 .1 amp. v ves) I ! to 1 hour

Between .4 and .45 amps. (Example : 3 valve set with

I 1 to 1t hrs.

2 .1 amp. valves and 1 .25 amp. power valve)

Between .5 a~d .55 amps. (Example : 5 valve set with 5 .1 amp. valves)

11 i to 1 t h rs.

Etc., etc. Etc., etc. I Etc., etc.

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lnstruction(Jor Connecting

Trickle Charger Model No.

for A.C. Mains.

Output-2, 4 or 6 volt at t amp. for trickle charging accumulators continuously. (Read Paragraphs Nos. 1, 3 and 5 of" Notes for All Models" page 1.)

1. ·Connect Mains Sockets in base of Unit as described under paragraph 1 of " Notes for All Models " on page 1.

2. Allow the accumulator to remain connected to the receiving set as usual.

3. Connect the accumulator to the Charger as follows :-

(a) Connect the negative terminal of the accumulator to the extreme terminal-(marked " N EG.") of the Charger.

(b) Connect the positive terminal of the accumulator to the terminal on the Charger marked " 6v " if a 6 volt accumulator is used ; to " 4v " should a 4 volt accumulator be used, or " 2v " if a 2 volt accumulator be used.

4. Insert the adaptor into the supply socket, switch on the current and the accum­ulator is on charge.

If the Receiver is in normal daily use the charging periods for the accum­ulator should be as long as possible. In any case the actual times should not be less than those given in the 2nd Table on page 5.

NOTES (FOR MODEL T.C.1.)

When on charge, it is not necessary that the accumulator remain connected to the Receiving Set.

When charging, switch off Receiver valves. ·when Receiver is not in use, detach adaptor of Chargerfrom supply soeket. Do not allow the metal case to come into contact with any exposed connections or metal parts ofthe Receiver. Make certain that the connections between the accumulator and charger and mains are correct as described above, as otherwise damage is likely to be caused to the Rectifier.

Important. Make sure that the ·charger connections to the accumulator are never reversed.

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Instructions for Connecting

Model D.C. 15;25 for D.C. Mains

Output- With insulated Screw-Connector in base connected to socket " 25 m.a."

S.G. Tapping H . 70-85 volts at up .to 1! m.a. for screens of screened grid valves.

L. 60-70 volts at up to 1! m.a. for screen of screened grid valve.

50-80 Volts Adjustable Tapping. Adjustable in 3 stages by bridge between 50 and 90 volts at up to 3 m.a.

120/150 Volt Tapping (with other tappings in use). 120 volts at dpprox­imately 21 m.a. up to 150 volts at approximately 11 m.a. (or if 50-80 volt tapping is not used then approximately 120 volts at 25 m.a. up to 150 volts.at 17 m.a. can be obtained).

Low Output.-With insulated connector screw on base connected t() socket "15 m.a."

S.G. Tapping H. 70-85 volts at up to 1! m.a. for screens of screened 'grid valves.

L. 60-10 volts at UIJ to 1 i m.a. for screen of ~creened grid valve.

50/80 Volt Adjustable Tapping. Adjustable between SO and 90 volts at up to 3 m.a. according to position of bridge (H.M. or L.).

120/150 Volt Tapping. (With other tappings in use) 120 volts at approx. 11 m.a. up to 150 volts at approp::. 6 m.a. (If the 50-80 volt tapping is not used, then 120 volts can be obtained at approx. 15 m.a. up to 150 volts at approx. 10 m.a.)

INSTRUCTIONS.

Read " Notes for all Models " Page 1. with special attention to Paragraph 5.

(There are no mains Voltage adjustments to make with model D.C. 15/25.)

1. Important. EARTH WIRE. It is most essential in operation of D.C. power Units that no earth connection is made direct to the receiver. There­fore before connecting the Unit, detach the " Earth" wire from the Earth terminal of the Receiver.

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2. Connect the Earth wire to the terminal ". E " in the base of the Unit. ON NO ACCOUNT MUST THE EARTH TERMINAL OF THE RECEIVER BE CONNECTED. (The receiver automatically obtains an earth connection thrvugh a condenser connected to H.T.- inside the Unit.)

Important Note. An Earth Connection made direct to the Receiver will cause damage !O the Unit, Receiver and Valves. A breakdown in the insulat­ion of any part of the Aerial System will have the effect of " earthing " the Receiver, and therefore it is essential to connect a small condenser in series with the aerial terminal of set and the aerial lead-in ; io other words the aerial wire should be connected to one terminal of the condenser and then another wire taken from the other terminal on the condenser to the aerial terminal on the receiver. The Condenser may be of any value between .005 and 2 mfd. and fixed close to, or inside the Receiver and will comply with R egulation No. 133B ofthe I.E.E. rules.

3. If 25 m.a. current output is required, insert insulated Connector-Screw into socket" 25 m .a. " in base of Unit and screw up gently until tight. If 15 m .a. current output is required, insert Connector-Screw into socket " 15 m.a."

4. Remove existing plugs from the H.T. wires of the Receiver and attach those provided with the Unit. Make sure good tight contact is obtained and then insert plugs into Unit output sockets to the required voltages. (See page 3 for method of connecting plugs to wires.)

5. Connect the Unit to an electric supply socket and turn on the current.

6. Switch on receiving set as usual.

7. If no results are obtained reverse the adaptor in the supply socket.

8. The R eceiver should now operate satisfactorily, but the screened grid H.T. feed (if used) should be tried in each of the S.G. sockets provided on the Unit and left permanently inserted in that one giving the best result. The bridge plug is for the purpose of adjusting the output from the 50/80 volt tapping and should be tried in each of the sockets H.M. and L. (High, Medium, L ow) until the most satisfactory results are obtained.

Note. This model will only operate with the adaptor connected one way round in the supply socket. It is advisable once the correct position has been found to mark the adaptor in some manner so that in cannot be inserted incorrectly.

DO NOT EARTH THE RECEIVER DIRECT. Leave the earth termina of the Receiver entirely unconnected. The earth wire must not be connected to anywhere but the terminal " E " in the base of the Unit.

Read " Don'ts " on Page 10.

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NOTES ON THE RECOMMENDATIONS OF THE INSTITUTE OF ELECTRICAL ENGINEERS" FOR THE INSTALLATION OF RADIO APPARATUS CONNECTED TO PUBLIC OR PRIVATE SUPPLY MAINS."

All "EKCO" Mains-Power Radio D evices comply with the Recommend­ations of the Institute of Electrical Engineers recently published, but certain recommendations apply to the installation of such apparatus for which we append the following notes relating to D .C. Apparatus.

129. " Protection of Live Parts. All parts (including the terminals and con­nections of batteries) which are alive or are intended to become alive from the supply mains shall be so guarded as to prevent accidental contact with such parts under normal conditions of use." Exposed terminals and metal parts of the receiver and accumulators are likely to become alive and arrangements should be made that accidental col!tact cannot be made with any such parts.

130B. " Any containing case made of conducting material shall be earthed in accordance with Regulations 101 and 102, and shall be provided with a suitable terminal for that purpose." On " EK.CO " Units the metal case is connected to a terminal which is provided for co1mecting to the earth wire of the receiver. .

131. " Protection against Excess Curre nt.- The apparatus shall be adequately protected by fuses on both poles of the circuit supplying it." This regulation is automatically complied with in most cases by the already existing distribution fuse boards in the house lighting circuit. According to the regulations however, tire pair of fuses feeding the circuit to which the apparatus is conuected should not be larger than 25 S .W .G. lead-tin alloy or 3-amp. fuse wire. If power or heatin" circuits are used, two fuses should be installed to protect the socket to which the Unit is corrnected.

132. " Exte rnal Cable Connections to Radio Apparatus.-Where the con­ductor of any cable connected to a radio apparatus is in direct connection with the supply mains, such cable shall be of one of the types specified in Regulations 76 to 81 and shall be installed in accordance with Regulation 87." The ordinary standard double vulcanized flexible cord as used for electrical fittings etc. is quite suitable for connecting the Unit to the receiving set. '

133A (for D.C. Units only) " Isolation from Supply Mains.- Earthing Lead. There shall be no connection except through a condenser , between any conductor directly connected to the supply mains and the earthing lead of the radio apparatus which is connected to the earth plate, wateq)ipe O.li.. other earthing system. T he above condenser should preferably be incorporad!H in the radio apparatus or should be placed as close as possible to it." This condenser is already incorporated in the D.C. Unit.

133B (for D.C. Units only). " AeriaL-W here radio apparatus is connected to direct current supply mai.J:ls, the aerial shall ~>nly be conne.cted to the apparatus through a double-wound h1gh frequency couplmg transformer adequately insulated for a test pressure at 600 volts, or through a condenser inserted in series with the aerial circuit and immediately adjacent to the aerial terminal. The above trans­former or condenser should preferably be incorporated in the apparatus or should be placed as close as possible to it." The method of connecting this condenser is described itz the instructions for Model D.C. 15/25.

133C. " Head Telephones and Loud Speakers.-These shall be connected to the radio a~paratus ~ither through a double-"":ound. transformer or, alternatively through a c!,rcmt wh1ch !ncludes a condenser m senes w1th each of the outgoing conductors.

Suitable Transformers are obtainable from most Radio Dealc1·s.

9

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1. DON'T use an unsuitable Unit for your receiver. If inferior results are ob­tained make sure that the Ul)it is rated to give sufficient current for the receiver. Also make sure that the H.T. plugs are in the correct position.

2. DON'T touch the internal wiring or components of the Receiver without first removing the adaptor from the supply socket.

3. DON'T imagine that the " EKCO" is responsible for each and every little fault, failure, or parasitical noise; a run-down accumulator, loose connection, faulty valve, atmospherics, heterodyning, oscillation or other nuisance may be the cause. ·

4. DON'T use a D.C. Unit on A.C. mains (without a rectifier) or vice ve.rsa.

S. DON'T short-circuit the output tappings or leads.

6. DON'T, in the case of Model D.C. 15/25; earth the Receiver direct or make any connection to the Earth terminal of the Receiver. ·

Suggestions for the- Elimination of

"HUM," "RIPPLE" ·or "MOTOR BOATING."

The users of an " EKCO " Unit is unlikely to be troubled with " hum ,., " ripple " or " motor boating " except in very rare cases, where the circuit of the receiver does not quite adapt itself to mains operation. The interference can usual­ly be traced to one or more of the following :---,

1. Transmitting Station " hum " which may be tested by tuning m another station.

2. An inefficient " Earth " connection. 3. An inefficient grid leak. 4. Incorrect amount of grid bias to the L.F. valves. 5. Although the Unit is screened by its metal cabinet, it is advisable if " hum "

is present to try it in various positions relative to the receiver. 6. The flexible cord connecting the Unit to the mains, or the mains themselves

may run in close proximity to. the aerial, or aerial circuit of the receiver. It can easily be determined whether the hum is being induced by the aerial by disconnecting the aerial from the receiver. If the hum disappears, then the aerial itself is inducing the hum.

7. If the Grid Leak of the detector valve is connected across the two terminals of the grid condenser or to L.T. negative, " hum," if present, can sometimes be eliminated by connecting the leak from the grid of the valve direct to L.T. positive.

8. Should a rhythmic beat, " motor boating " or " hum " be in evidence it can usually be eliminated by reversing the primary connections of the L.F. Trans­former. If more than one transformer is incorporated in the receiver, only one need be reversed. In sets employing 2 stages of L.F. amplification the rhythmic beat may be due to the fact that the detector valve is fed from the same H.T. tapping as the L.F. valves, in which case a seperate H.T. lead should be proviqed f9t the detector valve. The L.F. valves ca11 then be con­nect~d to the 120/150 socket of the Unit and the detector valve to an inter­mediate tapping.

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Alternatively, improved results may be obtained by connecting the last valve to a separate tapping ; this alteration can in most cases be quite easily carried out without altering the internal wiring of the Receiver, by disconnecting the positive loud speaker wire from the receiving set and reconnecting it to the 120/1 SO socket of the Unit. The H.T. positive wire or wires of the set may then be connected to an intermediate tapping.

In the case of receivers employif1g more than one Screened Grid Valve, the H.T. supply to the anodes and screening grids should be de-coupled in the receiver itself, and in th~ ~v~nt of trouble being experienced due to the absence of this de-coupling, the necessary resistances and condensers should be added to the receiver.

In the event of" hum " or " motor boating" being incurable by any of the above suggestions, try connecting a 4 mfd. condenser from one of the H.T. pos­itive tappings of the receiver to H.T. negative. The condenser should be inside or as close to the receiver as possible. It will probably be found that the con­denser has most effect when connected to the highest tapping.

CAUSES OF NO RESULTS.

(a) A faulty power supply. Test by connecting or inserting a lamp in the socket which is to feed the Unit. If the lamp lights up when the current is switched on then the power supply is O.K.

(b)

(c)

d)

A faulty connection between adaptor and the power socket to which it is con­nected. Test by applying slight pressure to the adaptor and moving it slightly backwards and forwards in the socket with the receiver switchecl,.on. If results are obtained when this is being d'one the socket or adaptor requires adjust­ment. A loose or broken connection on the receiver or Unit. Adaptor wrong way round in socket in cast. of D.C.

THE " EKCO" GUARANTEE. " EKCO " All-Electric Radio Receivers and Power Supply Units are· fully guaranteed for a period of 12 months from the date of purchase, and will be replaced or repaired free of charge shoulcl. they break down under fair wear and tear witHra the period named, provided that the Unit has not been tampered with or opened in any way and the instructions sent with each Unit strictly adhered to.

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