Questions and answers

Radio Record, Volume IV, Issue 41, 24 April 1931, Page 13

Questions and answers

C F. (Ohura): I can receive 2YA on * 70 on my dial when the normal gaye comes in at 17. 7ZL comes in at 4 A.: This is a rather puzzling phenomeion and is probably due to your set oscillating. You are really receiving a harmonic of your own receiver, which is being modulated by 2YA’s frequency. _ 2. Could you give me some of the staon the very long waves? A.: Leningrad, Russia, 1000 m., 20 k.w.; Oslo, Norway, 1071 m., 75 k.w.; Moscow, Russia, 1304 m., 165 k.w.; Daventry, 1554 m., 35 k.w.; Zeeson, Germany 1635 'm., 35 k.w.; Lahti, Finland, 1796 m, 54 kw. "PHANKEFUL (Te Aroha): What kind of circuit is my set? A,: We have not encountered such a one before, but presume that it is of the neutrodyne type and we do not know who the New Zealand agents are, 2. Could I add a pentode valve? A.: Yes. You merely place the valve in the last socket and connect the auxiljiary terminal to the highest "B" voltage btainable, R24: (S. Dunedin): I can only get ° a .00015 differential condenser. What change will I have to make in the coils? A.? Put from 15 to 20 extra reaction turns on. ‘There will be no need to make any other alteration in the set. 2.. What is the ratio. of the trans: former?-343 or 5-1. wase (Te Kinga): I have made the Daniells Charger and it is showing 10 volts’ for 10 cells. How can I increase the voltage? . A.: Provided the charger works satisfactorily we would not worry about the voltage being lower than it should be. This may be due to the load being placed by it. Furthermore, it may be due to defective cells, which, however, we considér unlikely, Test each cell separately to ¢liminate any duds. You can increase the--voltage by using more cells,

K H.D. (Mount Hden): Can I procure * valves other than those used in my three-valve set that will do the job as efficiently as those now in use? A.: We very much doubt if you will be able to do this. These valves are not generally used here, and the ordinary valve will not do. Try Whitcombe and Tombs, Wellington. 2. Can I replace any one without having to renew them all?-Yes. (TRANSMITTER (Kerepeehi) : I wish to build a really powerful broadcast receiver using a.c, valves, Can I build the "Outspan"? A.; An. excellent one is described in the "Radio Guide." It is called the A.C. Radiogram Five, but if yon wanted one still more powerful you could add another stage of s.g. radio, constructing it exactly as described for an existing s.gstage. S O. (Whangarei): I believe the cor- * yect number of turns on a primary coil to match my s.g.:valve should be 77. Is this correct? A.: No; the effectiveness of a large number of primary turns falls off rapidly after about 30. For your valve you should be using about 40 turns.

2. Can a pushpull output impedance be used satisfactorily with an ordinary cone speaker ?-~Yes. H C.W. (Khandallah): Can you re- * commend a good super. het. s.w. circuit of the battery type? A.: We do not know of any commercial receivers of this description, You could, however, have one of the local firms make one for you. QoL (Te. Aroha): What causes the musie to be muffled and rattly? I use a battery set with a "B" eliminator and a horn speaker. A.: This sounds like an inadequacy of grid bias or it may be caused by your not using an appropriate power valve. Furthermore, your speaker, which igs out of date, may be at fault. L C.A, (Aramoho): Should I be able * to receive American and Japanese stations on my set? A.: The Japs are not coming weli at the present time and the American stations are difficult to receive except in certain localities. If you can bring the Australians in at good strength your set is doing all that it should. 2. Is the valve combination satisfac tory? A.: Yes, but when renewing your valves get them all of the same make and be sure they are first grade. 8. How is the earth system? A.: It appears to be quite satisfac. tory. It ig better if the distribution point is nearer the centre of the earth pipes for then the leads to each can be equalised. ' WIRE (Dunedin) : I wish to construct a power pack for the super. het. s.w. adaptor using a transformed core of idin. x 11-8in. What number of turns must I wind on? ‘A. Primary 1125 of 34 gauge, secondary 1080 of the same gauge wire. Filament 9 turns of 18 gauge. P (Carterton) ; Can I, using an insulat- * ed wire, shift my set to another -room and plug it into a separate electric light socket, but using the same aerial and earth? A.: Yes, efficiency will be only slightly decreased because of the long aerial and earth lead, but you will get quite satisfactory results. Note.--The set to ‘which you refer is an excellent one and you may be assured of getting good results by ueaing it.

[{QUISITIVE (Motueka)-: A report the set to which you refer appeara about twelve months ago. We will pro ably have more to say about it im the near future, Tite valve to which you refer has not yet been to the laboratory so we cannot tell you anything about their life, which, from what you state, appears to be less than normal. 2. My "B" batteries are only .a fort: . night old and the "A" battery is well charged, yet if the set is left for about 24 hours it will go splendid for. about 10 minutes and then become quite dead. If turned on- within another half an hour or so it will be quite normal. = «© ~ A.: This seems to be a broken down eondenser, or resin joint. Tug all your joins and test all condensers. wh ta HJ. (Mangaweta): Will the circuit ® which I enclose be satisfactory for broadcast reception if I alter the oils and condensers? ° A.:Yes, but if you want a powerful set, why not build the Outspan ‘ Five, which we consider to be better than the one the circuit of which you enclose, 2. Will I be able to eliminate the poten’ tiometer return or the gri ae You may be able to. Potentiometer grid returns ensures smooth regeneration. 8. Will one rheostat be sufficient to break down the "A" supply from six. volts to four? vou A.: Yes, if you use 30 ohms.. ~ -4, Do you think "A-" instead of "A--" should be earthed? A.: No, your set is designed for an "AL" return. : GHUNTER (Mercer): I do not under-. stand what coil goes into the valve socket on the right of the s.g. valve. On looking through back numbers I find -~ ne, ee ee

Next Week’s Construction Feature | "A WAVE TRAP FOR LONG AND SHORT WAVES" Future Articles: "THE RANGER TWO" "THE KESTREL THREE" These will be good; watch for them.

(CKoRRESPONDENTS must attach this coupon to all queries sent « to the Technical Editor (Box 10382, Wellington. Limit three questions, pales letter is accompanied by 1i/ee, Name of set ....rcccsccccccvovesce Number of Valves csasescevsccctenne Name ececccccccccccvesecusnceuces Address eeeeocesecossevoeaeeveeene Nom de plume Coreoeseereeseseses — To be kept in subsequent inquiries. Date eeeee ececcerecce ecccearss Please Note:(1) Be specific and brief, sabulating, if possible. (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 supped, which may be quite inadequate, Intricate and involved specifications cannot be supplied without a specialist’s fee. 7

that only one coif has been specified and must be slipped over a five pin base. _ A.: With the Differential Four there is no need to use a coil with a 5 pin base for the radio stage,.or for that matter, the detector stage either. You will need to construct a coil with the secondary and primary only for the first stage..The coil will require three connections. We have designed the Differential Four to allow anyone who contemplates making it as a whole to build up this coil with three terminals, With the .0005 eondenser tuning the radio stage you need 90 turns on the secondary and 35 turns on the primary. The bottom of the pri-

mary and the bottom of the secondary will be brought out to "P,’’ the top of the secondary 0 "G" and the top of the primary to " With a-.00035 condenser in the second stage ycu need 105 turns for the secondary and 40 turns for the reaction. The ends will come out as described for the one yalve version. — 2. I have a quantity of 32 ds.c, wire on hand. How many: turns must be wound on a 2in. former to cover the broadcast band if IT use a -0005 tuning condenser ? } -D5,

N. Z.D.X. (Auckland): How can T use the three valve r.c. coupled set with the frame aerial? A.: If will be unsuitable. You should us? sets with regeneration, A suitable hook-up was described some time ago for the "Rotorua Portable," 2, Is a single wire counterpoise as’ efficient under a double areial as a double wire counterpoise ?-Y¥es. 8. Must a separate wire be taken from each wixe of the Pierce earth system to the set? A.: It is better to do so, , although you could couple the wires together and take a single lead to the speaker, UEBSTIONMARK (Wellington) : "Why is regeneration unstable with the enclosed circuit?

A.: The circuit appears quite satisfactory. It may possibly be explained from the layout. However, try a potentiometer across tlie "A’ supply and take ‘the grid return to the variable tap. 2. Is resistance controlled regeneration better than ordinary condenser or differ: ential control? A.: Resistance controlled. regeneration for shortwave is one of the best methods, We reproduce a diagram . showing :the method of applying this ayaterm.. Query (Waikato)': Can you give me the Jegend for Figure 3 in the 1981 "Guide"? . L, Li.-st Det. Coils... L2, L3,: L4.-Oscillator Coils. RFC.-Radio Frequency Choke. T.-Filament Transformer. R.-5,000 ohm Variable Resistance. RL -i, 500 ohm Resistance. R2,.-60 ohm Resistance. ; O-.1 mfd. By-pass Condenser. : . C1, C2.-.00014 mfd. Tuning Condensers. C3.-.0005 mfd. Condenser, C4,-.0005 mfd. Semi-variable condenser. C5,-.00005 to-.0001 mfd. condenser. 2, Would a shield similar to a single sheet partition in‘'s.g. receivers: be suitable for separating- the detector and os: cillator stages of the adapter? A.: They are probably .a little light and it will be necessary to shield ‘the stage entirely. 8. Does "C1" need to be, vernier, con trolled? ; A.: It is not essential so long as contro is finally geared, =; :

‘ORTHENDER (Dunedin) : What | number of turns must I wind on my dynamic speaker chassis in order to make a -high- voltage speaker to pass -70 m. amps ? A.: You will require about 341b, of 34 gauge wire. You will wind.on approximatély 19,000 turns. The resistance will’ be approximately 2000 ohms and will drop your voltage 120, RAvrI0. FAN (Otakiri):° Where ¢an I obtain. particulars. of the Daniell cells charger? A.: The "Radio Record" dated Novem- . ber 7, 1930. 3 2. Would a Beverage aerial pointing N.E, be successful if. it had to. pass over a hedge 15 feet high? A.? Yes, it would be quite satisfactory. It may: be ‘better, however, to take °: it north-west, from which direction. the Australians would come in. 3. Is the underground serial as deseribed in the "Radio Record" some time ago successful? We do not know anything ‘about it. was published merely as A sugges: ten from a correspondent. _ 4, Can I use the parts of an old five‘battery set to. make. a: short-wave adapter? . A.: Your condensers are too large, otherwise most of the components ¢ait be user 5. My: earth is’ only a 3ft. pine in dry. sandy ground. I intend to install a multipine earth and then connect these toa longer one in a hollow of heavier ground. Will this be better ?-Yes. 5. Would B605- improve reception or reduce the volume too much? A.: It would give you improved tone. but would slightly drop the volume. Vould’ a 180-yvolt battery improve the’ ‘set ?-Yes. ' You would need 9 volts bias or 15 volts with a B605, Our’ corespondent ‘adds:‘"I have been saving up these questions to save postage -(Seotch, eh?)" Yes, but you, have forgotten our bob-too Scotch, eh? EGINNER (Auckland) : I. have made the knife edge rejector . from. , the "Radio Guide," but’ have not had any _ success two miles from 1YA, . What: value fixed condenser should I have used? A.:°,0005 would be far better, ‘than 001, though you ‘shoulil not .have a great deal of difficulty in cutting out 1YA. This works ,Derfectly ‘right under the’ shadow at