QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 11, 25 September 1931, Page 13

QUESTIONS AND ANSWERS

FRANK

KEE

The Technical Editor will, through these columns, be pleased to help readers experiencing trouble with their sets. Queries are limited to three-for more than this a shilling fee is charged, and a similar fee is payable for queries answered by post. Supplying layouts, circuits and solutions of intricate theoretical problems is beyond the scope of this service. A coupen must accompany all requests for information. Nonappearance of the coupon in any issue cannot be regarded as a reason for its not being used. Address all queries, The Technical Editor, Box 1032, Wellington.

St P-UP (Greymouth): We regret that your query for coil specifications for all the amateur bands is quite out of the provinee of Questions and Answers. . It would take us a considerable time to work out all the details you want. Full particulars were published and all bands were given when the article wags published. Beyond this we cannot help you. 2, I have built the "Kestrel Three," but have Omitted series condensers for altering the wave-band. Do I make any other alterations so as to use the set primarily for shortwave? A.: Not if they are that type of alteration, for the series condenser in the aerial was put in because it was really necessary. If you use a separate primary you are losing strength. If you couple it directly in, not only would selectivity be poor, but you would be contravening the P. and T. Department's regulations, Did you really think we put that series condenser in for fun? If you want to make the get primarily shortwave use .0001 tun- ,/ ing condehsers with a special shortwave choke, 8. I intend te erect a half-wave Zeppelin antenna, I have a 60-feet pole and about 110-feet space. Could you give me the particulars for erecting one, with regards te height, length, feeds, ete.? A.: Height should be about 40 feet. Use eight wires, spaced evenly on insulating hoops. Height for 80-metre band about 60 eet. 4c (Dunedin): I enclose specifications for a power transformer for transmitting purposes. Are they correct? The core is 1 3-Sin. square, winding length Sin.

I am reckoning on approximately 3.9 turns per voli. A,: No, your specifications are not correct. You must reckon, for your transformer, 4.2 turns per volt. This works out 1000 turns for the primary and 1680 turns for the secondary on either side of the centre tap. You could use 24 enamelled wire for the primary and 28 gauge for the secondary. our transformer will deilver about 120 watis. T.C. (Wellington): Would you give ® me valve base coil particulars for the "Round the World Shortwave Three"? A.: Those given in table 4 in the list of specifications published on April 2 would just about sult your requitements. I HAVE a pair of headphones in which the magnetism has apparently been destroyed by knocks. Is there any means of re-magnetising them? A.: No; remagnetisation of phones is 2 difficult task and one which should be left to an expert. Even then it is not altogether satisfactory. UBX (Picton): Do you think I am using the most guitable valves for my American set? A.: We think you would be better to change PM6 for RCA221. PM6 could be used in the last stage in the place of 1124, but there would be little or no improvement. It would, however, provide an extra power valve should it be needed. It is possible that 221 would be better than the valve you are now using in number one socket. 2. When I am listening to stations on the higher frequencies, a high-pitched, powerful rushing, whistling noise results, which ceases abruptly if f turn the tuning-dial round to beyond 32 on the seale, : This is due to your set not being neutralised, and if you do not know how to go about re-neutralising it, it would not be a bad plan to get someone to neutralize it for you. Quite possibly the use of the valves we have suggested in the first stages would clear up the trouble. but we really think it will have te be re-neutralised, t is only a short and inexpensive job. H BR. (Greymouth): How can I make emy set more selective? It ig a fourvalve regenerative, separate primary for broadcast work. . A.: Without reducing your or introducing other losses, it is almost impossible to make the set more selective. You could do so by adding another tuned stage, that is. using a coil of, say, 78 turns on a 2in. former, 26 d.s.c. wire, tuned by a .00085 condenser, Connect the aerial a third of the way down from one end. and take the lower end to earth. Connect the top end to the present aerial terminal of your set. Connect the e also to the earth terminal of your set, This will make another tuning dial, bet it wil} sharpen selectivity, There will be alight losses. 2 Would a midget condenser in the aerial lead give improved selectivity? A.: Yes, but there would be a logs in signal strength. . if an additional stage could be added would it need to be shielded? A,: Not unless it were sereen-grid, An extra stage would be quite possible. but there is no need to use a valve if you use the tuner we have described. UPER-HET (Christchurch): I wish to build a battery super-heterodyne adapter, using G16 and G0. Weuld these valves be suitable?

A.: Yes, they will be quite suitable. Use 615 in the oscillator and 609 as detector. A cireuit for a battery adapter was published in the "Radio Record" a few weeks ago. It will be republished in the "Questions and Answers" booklet, which is now on the way. 2. I have a home-built two-valve shor! wave set, with valve base coils and two variable condensers, one with 7 plates and the other with 11. Is it possible to use these? A.: Quite possible. The first condenser ig a ,0001, and the second a .00015. The latter can be-used in the super-het, cirewit, FE eMoNT (Midhirst): Commencing at the top of the dial, volume control can be used full open, but as the dial is rotated the set breaks into oscillation, and

when volume is turned back, it plops hadly. A.: This points to a defect in the. rf. cireuit, probably a broken-down by-pass condenser. Possibly a condenser across one of the v.t. biassing resistances. 2, When the set is working on a station, reception is quite good, but it is accompanied by a slight hum, and when volume is turned back the hum disappears with a plop. A.: This sometimes happens and is due not infrequently to a defective valve. However, it is undoubtedly coming from the same source from which the oscillation is arising. 3. The condition exists right down the dial, except that the lower the position on

ORRDSPONDENTS must ettach this coupon to all queries sent to the Technical Aditor (Rox 1032, Wellington. Limit three questions, unless letter is accompanied by i1/ee, Name of set sere oaoosooogoocsoee Number of valves oocccoceccoocwscee Name #80 e0000000000@e9 00000000000 Address SOOSOSOTOCOOCSOCE0OOOOSDO000 Ne "©8288 SEDO O9S9GGO000H04S80000080080000 2908989000 8098 8000989890 800020000000 Nom de plume eeecoeeoeoeooo soo oCCKNeE To be kept in subsequent inguiries. Date FPOROCSSOBeorT sO FZ ALOSC OC Oe Please Note:(1) Be specific and brief, tabulating, if possibie. (2) Write legibly. and on one side of the paper. (3) We do not design circuits, but accept suggestions for feature articles Solving trouble, as different from advice, is difficult by correspondence and while letters are given every consideration, answers are not necessarily correct -they are only our opinion based on the matter supplied. which may be quite in adequate. Intricate and involved specifications cannot be supplied without a specialist’s fee.

the dial the lower the volume contro] has to, be turned. Av: There appears to be trouble with regeneration. Was it like this always? Ii 80, communicate with the agents who soid you the set, because undoubtedly there is something wrong with it. You say you contacted a serviceman who did nothing for you but charged you £4. We are very sorry to hear this, and wish we could do more for you, but when a serviceman is on the job and cannot help you, we cannot do a great deal by correspondence. Ask him to check up the by-pass condensers in the rf. stages. 7 ESTREL IIL (Motueka): I have recently completed building the ‘Kestrel Three." but have had trouble with the tuning on some wavelengths. Could you give me full particulars for the coils? A.!. Particulars for the coils were published in a panel with the Three," 2. Will a 8-1 transformer do in place of a 34: or 4-1?-Yes., 3. Why are the switches used across the 0001 mtd. condensers ? A,: The switches across the .0001 condeusers are used to cut them in and out of the. cireuit. When the condenser is in ‘the circuit the effective tuning range of the condenser is. limited; in other words, its tnuing condenser capacity is reduced to about...0001, which is a suitable value for shorfwave. When the condenser is cut out of the circuit the condenser is what it was originally intended to be-i.e., .00035, and is wveady’ for broadcast work. C, (Invercargill): Would a dual waye- * trap be suitable for eliminating one of the. local "B" stations, which blocks out 2NC, Neweastle ? A.: It would be quite satisfactory for absorbing two stations, but would be no better than an ordinary wavetrap for absorbitig one.’ If you do not have success with one particular wavetrap, try the onc that was described in the 1931 "Radio Guide?’ using two formodensers instead of the one formodenser and one fixed con-

denser. This wayetrap has been the most eificient of all we have described. T , (Te Kuiti).: I have an all-electric e six-vyalye radio set with a table model speaker, Can I have it converted into a dynamic, as we find, reception very poor during the day, although at night it is almost perfect, with plenty of volume?’ A.: The speaker has practically no influence over the set performance as far as bringing in stations during the daytime is concerned. You could use a dynamic speaker, preferably one of the inductor dynamics, but it would not improve the strength of your set one iota. It would inerely better the tone. VCONOMIC THREE (Gisborne) : Can two .00025 variable condensers be used for the "Kestrel Three’? If so, what would be the numbers of turns on the r.f. and detector coils? . A.: .00025 variable condensers are quite suitable: for the ‘‘Kestrel- Three." You need not alter the number of turns on the detector coils, but you would have to increase the number of turns on the broadcast coils to see 100 (30 dsc), tickler 40, primary 85, the wire for the two latter coils being 34-36 dsc. 2. Will you supply a few details of the rf. choke used in the ‘Record’ model of the "‘Kestrel Three"? . A.: The choke used in that set was an ordinary commercial one. . W.S. (Nelson): Would the cireuit I « enclose be quite suitable for shortwave ? : A.: The circuit is quite an orthodox one, and should be quite satisfactory. for short-wave work. However, if you want a really satisfactory short-wave set, try the advance a.c. short-wave receiver described in the ‘Radio Guide." It will give good results. However, the a.c. version of the "Kestrel Three," which you. have shown, will be quite satisfactory. Your resistances appear to be quite correct. 2. What is the filament current and amplification factor of C324?

A.: The valve is exactly the same as RCA-224, full particulars of which wave been published in the "Radio Guide." D R. (P.N.): In my commercially-made e receiver, which is about two years old, I am ‘using 226 valves.in all stages except the detector and last stage. Can they be improved upon? A.: No. In an all-electric set you do not have the latitude you have in an ordinary battery set. We should advise you to use the same type of valves throughout, and select a well-known make. , S& (Invercargill) -I intend building the "Radiogram Five’? battery model, described in the 1981 "Guide," but before doing so I would like to know the following :- + Is $625 suitable for the r.f. stages? -Yes. 2. Should it be shielded in the same manner a8 an ordinary upright valve? A.: No, it must be mounted horizontally _ With a vertical shield. 3. I have an .r.f. choke, the only particulars of which I have is the inductance. This .is about 1.5. millihenries: Is this suitable for the choke in the plate circuit of the detector? A.: Yes, the inductance is rather low, but still it should be fairly satisfactory. A IJ. (Ongarue): I have built a "B" * battery ‘from torch cells, but have not had complete success, as I cannot get any voltage. A.:. A special type of cell must be used in this battery if complete success is to be had. ‘These are those with a proper covering to the central element. ‘Some have a linen covering, or a linen pack, which holds the manganese dioxide and the central rod. You must use’ this type (found in most torch cells and in a certain super "B" battery), All the paste must be. scraped clear and then these packs placed in sal ammoniac. Use a saturated solution; that is, a solution of sal ammoniac and water that will hold no. more sal ammoniac. Place your zines in this and then connect, together the. zine and carbon rods of adjacent cells, The little cap on the carbon rods will provide an excellent means for connecting up the individual cells. L H.B. (Karioi): I have an all-wave * commercial receiver. On the shortwave lengths I-ean pick up 2ME, 3ME, and several New Zealand amateurs fairly well, and of distant stations I have had WX8AL, Moscow, London, and two or three unidentified foreign stations, but all very weak and distorted. ‘ Should I get more than this? If not, short waves, as a source of entertainment, are rather a failure, A.: You should be able to hear London in the early morning and Moscow, as well as the American stations, clearly and well. The American stations should, under fairly good conditions, come in at such strength as to provide real entertainment value. If you are not getting this we should suggest that you get in touch with the agent who sold you the set, as it is possible that there is some little fault with it, or that you may not be manipulating it to the best advantage. 2. On the broadcast wavelengths I get the main New Zealand and Australian stations moderately well, although without very.much yolume on the distant and small stations. I can get KFI very faintly, but no other American or Japanese station, Is there any way of increasing the volume of the distant stations? A.: We are inclined to think that your condensers are not balanced up. correctly; as you do not appear to be getting the results you should. We have tried this set out and have found that it is equal in all respects to the average commercial a.¢. receiver, and being such it should give you perfect satisfaction, Just look over your aerial and earth installations and. make quite certain that they are good... 8. The valves are SG442, two A415, and two B405.. Are these the best for the set?-Certainly. 4. Oceasionally the music fades right out, and on tuning the reaction knob over Y find the set will not oscillate. A sharp rap on the’ front panel brings it: in immettiately at full strength. ;

_ A.: This points. out clearly that there / is something wrong with your set. It in impossible to say what it is from -the © particulars given. It may be a defective resistance, a. bad connection in the set, or a condenser. We do not know and cannot tell without looking at the set itself. 5. The B batteries are of the largest size, and last six-or seven months. Do you recommend wet. B batteries?) How long do these last after each charge? A.: We would recommend wet B batteries if you had adequate means to charge them, but if you have to -send them some distance to be recharged, then we would certainly recommend you to keep to the dry cells which you are now using. You appear to be getting average life from them. The wet B batteries last about two years, and usually require charging every three weeks te 9 month. 6. Do you recommend "magneto B" supply instead of the B batteries? A batteries can be readily charged here by a small water wheel and a six-volt dynamo. A.: Providing your magneto — supply was sufficiently smooth, it would be ‘quite satisfactory, but we are afraid that ou would get hum. . $ "(1 RID" (Whangarei) : I wish to build the "Radiogram Five," and for the current supply. I propose to use the B accumulator and the A and B accumulator charger, both of which are described in the 1980 "Guide." If I built.the B accumulator, as described, would it supply sufficient current and * would the charger be capable of recharging it? A.:.The capacity of the battery will be about’ 4 mamps hours, so that the charges described in the "Radio Guide" will be quite satisfactory.

2. Supposing the capacity of the B ac- } gumulator were 900 mamps. hours, and "the total drain from the valves 25 mamps., would this meant that my B' battery would last 36 hours? vs A.: You can always compute the life of a B accumulator by taking roughly half the capacity; that is, dividing the mamps. hours by two. Then divide into this the drain taken by your set. It is most unwise to mun an acenmulator down more than half. The accumulator describéd in the "Radio Guide" would,. with a 25 mamp, drain, last 160 hours, Generally speaking, a B battery charger must be charged at double the rate of the drain imposed by the valve. That means that the charger must be on about the same length of time as the set-is operated. aoe vaives should I use in pushpu . A.: We would suggest the. B605. type, which will work quite satisfactorily from 1385 volts B, and give a higher output than the 112. The B charger accumulator, if the secondary were wound to accommodate 180. yolts, would be quite ample to charge this, You should wind ong 2100 turns on either. side of the secondary. , LNUMertaNaD (Stratford): I have an American set which uses the following valves:-A615 and PM6 in the first and second radio, detector "A615, first audio PM6, second audio B605.. Can you suggest any improvement? A.: We would suggest second radio and first audio 221. PM6 is not suitable for those two sockets as it is an output valve. RA: (Ohakune Junction): I have a it? Raytheon X210 valve. hat class is A.: The same as UX210, employing 17.5 volts on the filament and 400 volts on the plate. F J.M. (Pahiatua): If I obtain a radio e dealer’s license, do I have to have an electric wireman’s license to instal radio ts? No. You may instal a set providing you do not_interfere with the wiring of the house. You can connect the set up to

a hot-point, but if one has to be installed an electrical wireman must do this for you. GeLEcToR (Gisborne): We do not recollect having seen the circuit to which you refer. However, we shall hunt. up our files for you, and, if we can find the circuit, we shall send it along.

QGTALLOX (Thames): I wish to construct an auto-transformer to go between my mains. Would such be satisfactory ? A.: No. The regulations state quite clearly that a transformer, with a separate primary and secondary, must be placed hbetween your mains and any radio apparatus. Auto transformers employed in the manner you suggest are not at all suitable for radio work. . L H.S. (Bluff): You can tell me how to e neutralise a Radiola 20? A.: Remove the chassis from the eabinet and set up as for reception. Tune in a station about 1400 k.c. and then remove the second valve from the left and insert a dummy. By a dummy we mean a valve which is intact except that one of the filament prongs has been cut off, or is covered with silk in order to prevent it making contact with the socket, If this stage is neutralised the signal will disappear, but if it does not, adjust the neutralising condenser mounted on the rear edge of the valye panel and between the first and second valves until the effect is obtained. The adjustment is quite critical and must be done carefully. Once the minimum signals have been obtained remove the dummy and replace with the normal valve. Now replace number one on the left with the dummy and. repeat as with number two, This time adjust the condenser immediately under number one valve at the rear edge of the valve panel. These two condensers are of the small compression type, consisting of two plates separated by mica and adjusted by a central serew. ; Boer (Hikurangi): I am using a BD4 and have a 256 valve in the last stage with 90 volts on the plate and 9 volt bias. Am using an output filter, The bass notes do not seem to be over emphasised, although the high notes are not shrill, but the tone is not all that could be desired. My second transformer is a 5 to 1 ratio. ‘A. : The trouble probably lies in your output filter which was not designed for a power valve of the 256 type. If you.install a filter, preferably a taped one, we think you would get better results. Furthermore, a 6 to 1 transformer is not conducive to quality, and in itself? would account for the low note loss. You will not get very good reproduction with 90 volts only on the plate. 2; The symbol to which you refer is 2 centre taped LF choke.

A.P. (Otekaiai): I made a diagram of © a 4 yalve set. Could it be converted into an AC. If so, what changes would be necessary? Would I have to change the valves? . A. : You would certainly need to change the valves and you would have to adapt wiring to the indirectly heated valves. There are several circuits in the "Radio Guide," so we think your best plan would be to build up one of these. . R. Me. (Taranaki): I. have a 6 valve e set and cannot receive any American or Japanese stations. When I put my finger: on the aerial lead the power is greatly increased. A.: It seems as though your aerial is defective. Your body is then acting as an extra serial and so increasing the strength. If your aerial proper were fully efficient the little extra that your body picks up would not be noticed. Hxamine’ your installation very carefully. If you have & lightning arrester, take it out and see how the set then operates. Examine any soldered joints. Let the aerial down and clean the insulators, vite

2. What would be the approximate cost of the Outspan Five with all batteries and valves ? A, : Probably about £15. 3. Could the Sparrow Hawk adapter be used with the Outspan Five ?-Yes. H F.R. (Auckland): Would you give me e the number of turns of about 26 enamelled wire on 2in. former for the secondary and tickler windings to work the broadcast band, the secondary to be tuned with a .0005 condenser and regeneration by a .00015 differential condenser? A. : You people could save us a lot of trouble by looking these things up in the "Radio Guide." There is an_ excellent table published on Page 58. It has exactly what you wish to know about the secondary coil, and you could have experimented with the differential reaction. However, here are the numbers of turns, Secondary 88 turns, reaction 35. ® is there any advantage in using d.s.c, wire in this case?-WNo. 8. When mounting a screen-grid valve (A442) type is there any advantage to be gained by mounting the valve horizontally through a hole in the screen? A. : Theoretically this is the best way to mount the valve, as any chance of the stray capacities finding their way from the grid to the plate is then very small. Fricaro (Auckland): Is the 10 ohm resistance in the negative to earth between the bottom of the S.G. secondary coil and earth, or is it in the positive in the Radiogram Five circuit? A.: The Rheostat is in the positive lead. There is small biasing resistance in the negative lead between one of the filament terminals and the shield. This is merely a few turns of resistance wires. Unfortunately the displacement of the figures 30 in diagram 27 in the "Guide" would lead one to think that the small biasing resistance is 30 ohms. 2, What are the coil diameters and turns for the aerial coil using .0005 condenser?

A. : For 26 DSC wire 72 turns for second~ ary and 25 for aerial, ‘ 3. Audio oscillation is apparent when the speaker is placed on the set and more C battery is required on the first audio, Would it be overcome by using more modern speaker ? A. : If the set whistles when the speaker is placed on the cabinet it would appear that .you were getting microphone howl from the set itselt. If you place the sperker away from the set and gudio oscillati is not present you need not worry abot a more modern speaker. Audio oscillation ean possibly be overcome by reversing. the primary connection to one of e transformers. A B.C. (Paeroa): I wish to build a fourtke valve battery set. Would you please give me the names of suitable eircuits? A.: If you wish to build a really good four-valve set we would advise you to try the Differential. four, published in the "Radio Record" at the beginning of this year. G T, (Putaruru): My reception during e the day is not as I should like it. I have four pipes driven into the ground two feet apart outside the house, and from these bare copper wire leads to a piece of copper plate from which an insulated lead goes to the set. In all I have about 16 feet of copper wire. Is this too much for earth? _ A.: No, your earth appears to be’ quite efficient. Do you keep it well watered and have you tried the effect of salt upon it? 2. How could I get a better reception? A. : Have you balanced up the condensers of your set? If you look in the back of the set you will see four holes near the top of the canisters shielding the coil. If you put a screw-driver in these you will fing a little screw. Tune in a weak station and adjust these screws one after the other until the station comes in-at its strongest. You will find to get at these screws you will probably have to remove the rectifier and the 245. os

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