Questions and Answers

Radio Record, Volume IV, Issue 14, 17 October 1930, Page 24

Questions and Answers

Com (Northland): I wish to build ‘a battery charger such as that deseribed in the 1980 "Guide," but do not want the "B" side. What alterations gre necessary? A.: You will find full particulars of an "A" charger in the 1929 "Guide." 2. How: much current will an English dynamic speaker draw from an "A" battery? A.: Unless you give the name of the speaker it is impossible to say how much current it will take, Probably it will be in the region of three-quarters of an ami:. : 3. Where can I have a home-built transformer tested? A.: Almost every dealer: has an a.c. meter which he would put on your transformer. 4. Will the Loftin-White transformer

supply sufficient current for an extra 224 valve?-Yes. 5. Will I have to put on an extra filament winding ?-No. U X. (Te Kuiti): How many turns are ¢ required for transformers using a .00085 condenser, any gauge wire and ‘ any sized former? A.: Secondary 84 turns of 24 d.s.c. wire, on a 2in. former. The primary 25 turns slot wound. 2, On my present set I had 70 turns of 24 d.s.c. wire and the inductance was too high, for I could not tune below 8UZ, and I wish to tune 1ZD on 150. A.: The ordinary broadcast does not go down to 150. so we advise you to another coil with 30 or 40 turns. A 65-turn coil would be normal for broadcast band. ~ —

8. Can you tell me if the usual screengrid connections act as well as the spacecharge connections? A.: Use the ordinary screen grid, pre ferably transformer coupled. M (NAPIER): Would a pile of * stampings 1din. wide and #in. thick be satisfactory for the Loftin-White following the 14in. specification? A.: Your best plan would be to build the stamping up to full thickness, 1din., and redesign the winding in accordance to numbers of turns given on~page 55 of the 1929 "Guide" and-in the 1930 "Guide." If you cannot manage this yourself we could do it for you. 2. Will Pilot No, 377 choke be suitable for the transformer ?-Yes. 8. Details have been published of the L.-W. with r.f. stages. When are you coming to light with your description? A.: It is on the plan we have for future eonstruction items, When the d.c, eliminator is finished we will, in all probability, commence a series of receivers, working from a one-valye upward, following this a two-stage Browning. Drake, and then the L.-W. tuner. However, the bare circuit will be published before then. C J.M. (Bombay): What is the maxi- * mum output in watts’ when using the 250 valve? A.: We have not seen this stated definitely, but it must be in the region of 6 watts. 2. How much louder would signals be using a 250 valve with the 245? A.: A 250 can handle a greater output without distortion. It does not step-up the signals greater than does 246. If anything, it is less. 8. Will you explain how to connect the amplifier to the detector valve of the set? A.: The L.W. takes the place of the ordinary amplifier and is used after the first audio transformer. 4. What type output transformer would be suitable for either a magnetic ‘or dynamie speaker? A.: Most dynamic speakers are provided with a step-down transformer, so you should use a 1-1 or a tapned secondary would be better. and use this in conjunction with the 25-1 in the case of the dynamic speaker, F. A.A. (Hamner Springs): I enclose a plan of a receiver. What are your comments on it? A.: The receiver is evidently a very old one, and you will find a much better described in the "R.R." as the ‘Shielded Trive Neutrodyne. " Your diagram makes no provision for grid: bias which is essential if quality is desired. Furthermore, this circuit as it stands would ruin a power valve. The best valve would be 221 type in the radio and first audio sockets a special detector and a power valve of the 112 type. This combination cannot be used without bias. How far should I be able to reach? re That depends upon your locality. If it ig not very poor you should get the Australian stations quite well. 8. Could a sereen grid valve be added? . A.: Yes. It could take the place of either the first .or the second valve, but would need to be shielded.

4, What wire is required for resistances with the d.c. eliminator? A.: See this week’s instalment, P K.B. (Oamaru): Can I add another * valve to the Cossor Melody Makex? A.: Yes, another audio-stage was. {le scribed recently. : 2. How much will it cost?-About £2. 3. Can I change my set into an allelectric, and how. much? A.: It could -be converted satisfactorily if you had the requisite knowledge, About £10 providing "A" transformer. . 4, What stations operate below 200 metres?-Try the DX Club. H. J.G. (Wellington): Why can I hear * wireless with the earphones and the connections lying on the floor or in my hand? Forty years back when I was on a bush section in Taranaki I often used to hear music. Now I hear the same thiing only more distinct. A.: It is almost impossible to explain this phenomenon. You may have un-

usually sensitive hearing, but why it shoul respond to the rapid vibration of & transmitting station is more than we ,, can explain. Can you recognise the items hen you have the phones on? As to why you should hear the music in the backblocks we can offer no solution. It wasn’t on the air, so far as radio is concerned, at that time. Sounds travel in the air for a considerable distance, and with special instruments they can be interpreted, but to our knowledge it has not been done by the unaided ear. : J W.F.. (Dunedin) : What are the num- * ber of turns the size of wire, formers, etc., for the 5-valve Browning Drake to be used with .000875 ganged condensers? f A.: Use 2in. formers, and wind for the secondaries about 80 turns of 24 gauge d.s,c. wire. Primaries will-depend upon the valves used. A2.. Would a rotating tickler be better thin’ a condenser controlled one? A.: A rotating tickler would be easier to incorporate, but a condenser controlled would give better results. 8. Would 180 volts damage a 609? A.: Yes, reduce it to at the most 150, and if the valves are to be used in the radio position the voltage should be reduced to 90. F W. (Petone): Why can I receive * 4YA and 8YA each Wednesday evening on a home-made crystal set of the ee type, with a one-valve amplier A.: It may be due to reradiation, but it has been proved fairly conclusively that long-distance reception with a crystal] set is not an impossibility. Your variometer may be tuning too high to receive as low as 8YA. A S. (Wanganui): Can you supply a * diagram showing how to place an amplifier on a crystal set, and what sta"ations would I be liable to receive with it? Could I receive 2ZF in Wanganui on the set without the amplifier? A.: Full descriptions: of crystal set amplifiers have been described) in the 1929 "Guide" in "All About the All-Blec-trie," and several kinds in the "R.R." You would not be able to receive 2ZF on a crystal set and an amplifier in Wanganui, TH Atutu (Henderson) : Is 80 turns on a 2in. former with 24 gauge wire and .00035 condensers correct for the B.D. ?-Yes. 2. What is the correct number of turns and what tap for the aerial coil? A.: The same number of turns tapped at the 20th turn. 8. I am not clear on how a separate coil is used. A.: When we refer to the aerial coil of the B.D., we really mean a tapped secondary coil of the same dimensions as the other secondary coils (if tuned with the ame sized condenser), and tapped a short ay from the low potential end. If a separate primary is used it may consist of 20 turns wound over the secondary or a variable swinging coil like a tickler suspended inside the secondary. In this lat- . ter case the selectivity could be varied at will, though it would at no time be as sensitive as the tapped secondary coil. 4, I cannot get on to high frequencies, although when I bring the aerial in to the neutralising condenser results from 8YA. are wonderful, A.: It seems as though your aerial coil is not of the proper dimension.

three-stage rf. B.-D., but the reaction condenser appears not to act, and sometimes I get a clicking noise. ; ai This appears to be a defective grideak, _ 8, I tried another .0003 by-pass condenser without result, so I cut out the .001 condensers, and now the reaction condenser works quite satisfactorily. A.: The .001 was probably too large for your conditions. Try a smaller one. 4, I am using 615 for first audio. A.: 609 would be better. 5. How can I hook up an anode bend detector? ; A.: A diagram shows the idea. Take out the gridleak, short circuit the grid condenser, and connect the grid return to 8 volts negative C battery. Connect the +- to A-, and apply 90 volts to the detector valve. 6. Has the tickler coil to be spaced ?- Go DANE. Valley).-I am uéing 2 No. ce Is 11 turns correct for the 609 valve? -Yes. 8. For the tickler will the wire wound on a former like the secondary coil be satisfactory ?-Yes. 9. Where do you suggest the leakage is if not through the by-pass condenser? A.: There is no leakage, but blocking.

You do not mention what C battery you are using, and what voltage beside 135. If this is on all valves, it is too much for easy control. No more than 90 should be used on radio and audio, and the detector if leaky grid, 45. (CAMERON (Canterbury): Wellington seems to distort on my _ three-valve set, and neither of the rheostats seems to have any effect on volume.

‘A.: Have the yalves tested, increase the bias on the last valve to 9 volts, and _have the transformer tested. We. could have discussed your circuit had you sent a theoretical version, but it is impossible to do anything like this when a. sketch plan is sent. It would take considerable. time to unrayel. H.D. (Gisborne): Could you give * particulars of a heterodyne wavemeter? A.: See "Radio Amateur’s Handbook," obtainable at least from Te Aro Book Depot, Wellington. RESISTANCE (Christchurch): What are the numbers of turns for primary and secondary of rf. coils to suit the valve base coils described for the P.C.J.4 a short time back? A.: The secondaries are the same, and the primaries 60 and 120 respectively. The fact that you are using a .0001 condenser will slightly alter the tuning ranges. I G.A. (Wanganui): Reception on my * set is not as good as it might be, for I pick up a noise and only a factory is. near. . A.: This is probably coming from some of the apparatus in the factory. Remove your aerial and see if it persists. If it does communicate with the agent. 2. I find it difficult to bring in Auckland and Australian stations during the ay. A.: You are expecting too much-you may be in a bad locality for Auckland, and there are not many sets that can pick up the Australian stations in dayight. W G.R, (Ohakune): Which is the betWw we set, "R. the W. 2" or "R. the A.: "Three" is more sensitive, would cost another £2 or so to build, and would require more battery. The two-valve set was described in our issue of February 28, and the three-valve a week later. R W. (Bay of Islands).-What is * wrong when a five-valve set pro-

duces. no sound, when all the valves are used? All the best stations can be had on, the loudspeaker from the four-valve set. voit A.: Probably the power valve ‘has been burnt out or has‘lost its emission. Try another valve in the socket. The intervalve transformer. may be gone. Shift the last valve out: and: try it in the second last socket, and if .the set will. not go it is the last valve for certain. RRAD0x (Blenheim) -TI have a six-valve set, but cannot get the Japanese at speaker strength, What stations could I expect to get? A.: Your situation may be bad for the Japanese, and it is impossible to say if your receiver is at fault from the very meagre patticulars given. Your aerial and earth should be in order, and the former should be 40ft. high, and 70 or S0ft. long, if you want first-class results. The batteries may be a little flat, or there may not be enough of them. © MAH (Opunake).-How can the re sistance of an earth connection be measured ? A.: Apply to your electricity. supply authorities, who have the necessary measuring instruments, and would probably charge only the price of a fuse replacement. UZZLED (Westland).-How can I test a lightening condenser? A.: Remove it from between your aer ial and earth, and if the set goes better it ig at fault. If it does not make anp difference your earth wire is probably eorroded. A B.C. (Timaru).-When I connect the short inside antenna to my receiver I find that it goes much better if the

far end is touched with a piece of metal. Does this signify an internal fault?. A.: No, by contacting the wire you are adding to the effective. aerial. length, for your body is collecting © signals. W H. (Alexander): I have an Ameri- * can battery set. What is the best combination of valve? A.: Four 221’s and a B605 suitably biased, in the last socket, ~ Ke SHT: (Dunedin): I can get only morse on my all-wave set. The tuning coil ranges from 25 to 45 metres. A.: Wind a few more turns, say two, to get up to 50 metres, as most of the stations on telephony which are received regularly in New Zealand are transmitting. on 49 metres. Always remember when tuning a short-wave set if you want morse oscillate, if you want telephony, do not. The fact that you. are receiving morse proves you are oscillating. Stop this and you will receive telephony, which you cannot do otherwise. BAY (Christchurch): I have a three- _ valve set. What alterations must I make to convert it to a short-wave set? A.: We cannot redesign your set, but you will find an excellent adaptor described in the 1929 "Guide," but omit the 1 mfd. by-pass condenser, H.G. (Whangarei): In looking * through Q. and A. it is very disheartening to have to read of everything by its technical term. There must be hundrads of listeners who, although interested and desirous of improving their results eannot follow your page because of its technicalities. I have frequently asked people. to, translate the answers, but they reply in equally baffling terms, ~

_ A.: This is more or less inevitable. We cannot devote more space to Q. and A. | than they aré now receiving, and if we were.to attempt"to explain everything in everyday language the space’ required would be moré*than double. If you refer to the , "Radio Guide" of either 1929 or 19380, you will find all the terms explained there in non-technical language. However, .we will bear . your request in mind, and keep our replies as general as possible, » Jd T.S. (Wangatoa), I find that my "B" * battery of a hundred Leclanche cells delivers a 140 volts when standing, and 874 when using. They were supposed to deliver the same yoltage at all’ times; My set draws 28 amps. A friend of mitie has a similar battery, from. which he draws 15 amps. and his remains constant. . A.: This is due to the extra load drawn "by. your batteries. You see it is almost double. A peculiarity of Leclanche cell is that when a drain is placed upon it, polarising takes place, and the voltage drops. This is due to the collection of hydrogen bubbles around the zinc. In dry "B" batteries a depolariser is used. 2. What is the approximate life of the porous pots? I can see signs of wear on the zincs after.a month’s use. — A.: You will find the zines to wear fairly quickly, but the porous pots and their contents should last for some considerable time.’ N Z.R. (Christchurch). Will my set * be materially improved if I substitute six volt valves for two volt? The present valves are 18 months old, and I de not want to go to the expense of a six

volt battery if a two volt will do as well. A.: You would find the four volt series a good compromise. They are more sensitive than the two voli. 3. What method of. regeneration control would you advise where panel space does not permit the use of a variable condenser and a moving tickler is inconvenient. ae A,: You are certainly under difficulties. Resistance control, a diagram of which is published this week, should meet your requirements. L J. (Christchurch). My wave trap * will not cut out an amateur who js 500 yards away, though it will eliminate 8ZC in favour of 38YA, and vice versa, -: You appear to be in the shock area, and it will be very difficult to eliminate the amateur. If your aerial is not already at right. angles to the line between yourself and him, try and get it round. It will probably make a great difference. Otherwise you are unfortunate. SUCCESS (Napier). What type, of dynamic speakes would you recommend to give undistorted volume for a hall? A.: You do not state the size of the hall, but for medium size one that will deliver 10 watts will ‘be satisfactory. 2. I am troubled. with electrical interference. My aerial is at right angles to the lines, and I have tried a counterpoise earth all to no effect. A.: The first thing to do is to advise the power supply authorities, and see if they can prevent it. If they have done all they can, try another earth, an indoor antenna, such as wires between the ceiling and the roof, and loose coupling in the aerial circuit, . :