Questions and Answers

Radio Record, Volume VI, Issue 25, 30 December 1932, Page 22

Questions and Answers

8. (Christchurch): I have a com- © mercial a.c. radiogram, and when the switch which changes from gramophone to radio is lying at neutral and the volume control is right off, there is a noise like static. A.: Obviously a defective switch. J A.S. (Oamaru): I have constructed * an ac. set which appeared in an overseas publication. Commercial coils are specified, but no particulars of windings are given. Could you give me details of suitable coils wound on valve nage formers ? ,

The secondaries should be wound with 26 d.s.c. and the reaction coils with 36 d.s.c. Fi uel F. (Dargaville): I have built the * ‘*Nifferential Two? with an extra audio stage. Could you let me know the best type of valves to use and how many turns of 28 s.w.g. enamelled on primary, secondary, and tickler windings, using .00035 tuning condenser and .0002 reaction condenser? ’ A.: For valves, use two type L210 and a P215. You do not state the diameter of the coil former you are using, but assuming it is 2in, the coil particulars are as follow :- Primary 25-30 turns, secondary 75 turns, tickler 25 turns. If reaction is too fierce take a few turns off the tickler coil. D**wv (Wanganui): I have a 4-valve s.g. set, but since shifting to Wanganui from Gisborne I cannot get any Americans. A: Locality is an important factor of long-distance reception, and evidently your present one is not sé favourable as your last. Your aerial system appears to be quite sound, and we would not advise you to shorten it, as you suggest. "ATOVICE" (Auckland): I have a 5valve a.c. set and wish to make a s.w. adaptor. Where could I obtain a circuit? A.: In the 1930 "Radio Guide." 2, What stations would I then get? A.: You should get all the worth-while short-wave stations in the world. "PUZZLED" (Hastings) : I have a four valve set and I cannot receive 2ZH as loudly as 2YA. Are my coils at fault, and could you give me particulars of them? A.: If you can receive 2ZH at.a definite peak in volume, i.e., if there is a falling away in loudness if you move the dial either way, the set is tuning down to 2ZH’s wayelength all right. Possibly you are badly screened from 2ZH, but not from 2YA. After all you must remember that 2ZH operates with only one-fiftieth of the power of 2YA, 7 "L0Co." (Wanganui): Would tuning my aerial as per sketch be an improvement as regards distance and selectivity? A.:; Theoretically, yes, but practically we don’t think it would be worth while. E A. (Lower Hutt): I am constructing * the "Modern Five," which appeared in the: December "Radio Times," and am incorporating band-pass filter which appeared about two months ago. My condenser is a four-ganged one, of .00035 mfd. capacity. What would be the new coil specifications, using 80 gauge enamelled and lin. former? A.: Secondaries, 180 turns, primaries (link coils), the same as specified,

2, What would be the effect if instead of winding the primaries over the secondaries, they were wound on the former below, spaced 1-16in.? ‘A.: In the Link band-pass filter the primary is wound in this manner, 15 turns being close. wound, and 15 bunch wound. Overwinding would thus make the coup ling too tight. 8. Would the number of turns for the aerial coil be the same as in the other coil? Would it be wound over or below the secondary? A.: The Link band-pass filter does not use a separate aerial primary, but the aerial is tapped down the secondary. If you tapped your aerial at the 100th turn this should be O.K. H G. (Hamilton) : I have an eight-valve * commercial superhet, which has been in constant use for the past eighteen months. During the past month or two it has developed a scratching accompaniment to the modulation, that is to say, when the set is turned on the scratching is barely audible, but as the volume control knob is advanced so the scratching sound 3 increased. There is a continual accompanied rising and falling with the speech or music. All valves were tested a short time ago and are O.K. Dlectrolytics have been replaced but no improvement result ed. The set doesn’t seem to be as sensitive as it was formerly. A.: If, as you say, you have had servicemen in to examine the set, we are afraid we cannot help you much, The trouble sounds rather like a defective volume control or a broken down by-pass condenser, or resistor. W J.H. (Foxton): I have built the, * "Round the World Three," using three 201A’s with a "B" eliminator and ~ an accumulator. The set has now developed a squeal on short waves. I have tried altering the grid-leak, grid-conden-ser, transformers, chokes and coils, all in vain. A,: As the trouble was not always there we think it lies in either your "A" or "B" supply. Is your accumulator O.K.? Also, it may be a broken-down condenser or resistance in your eliminatae. In addition have your valves tested. A G.H. (Napier) : Can you recommend * a circuit to run a small dynamic speaker and capable of giving reliable reception of New Zealand stations only? Daylight reception of 2YA. and the local station would be required also. A.: You could not do better than either the "Simplicity Superhet" or the ‘Modern Five." Reliable and guaranteed kits of each of these sets can be

Information Coupon (To be used with all requests fdr information.) Name Of SCt sesccccscccccccesesees Model Name Address eeeeeceeesceaesseeoses eeeeaosas SSCSHHSSSHOSHSESSSSS SSS ESOSEE SSCSHTSSSOSESOSSESESOOSEEOS SCTCSSSSSSSSSSSSOSSSSESSCHSHESTESH SESE SSSSHSOSHTOHSSSOHOSSSSTSSSSEREEEECESESS Nom de plume .ccccccccsccccecces To be kept in subsequent. Please Note:(1) ie specific and brief, tabuating, if possible, (2) legibly, and-on one side of the paper. (3) We do not design circuits. Limit three questions, unless 1/- is enclosed. (5) Postal queries limit three questions. Bnclose stamped envelope and 1/+ fee, Mune

quite readily procured -from several of advertisers, . TYX18HB: What is the inductance of the special: audio coupling choke in the "S.W.C. Two" and where is it to be obtained? ° a A.: From 800-500 henries. Use the secondary of a high-grade transformer. 2. Where is the ,56 mica fixed condenser? ' ' A.: It is not absolutely essential to have a. mica .condenser other than the coupling condenser, though it may be preferable to use micas in other positions. 3. Round pigtail type condensers may be obtained anywhere. . 4, ©8, although it does not increase the internal capacity of the valve, increases the oscillation. It is really in parallel ‘with it and, of course, tends to reduce self capacity. ; ; 5. Our experience ‘with Osram valves is that they are excellent and one of the best type of battery valves. with which we have experimented. We have never found their emission poor and have very rarely struck a "dud." 6.-You can use enamelled wire without space, although it would be preferable to space it by its ‘own. diameter. 1 AGRA (Auckland): My present , aerial. is placed as shown in diagram. It is therefore best for Australians, but at present it is difficult to get the Americans on their morning session. Would an aerial under the roof tiles of 200 feet be as good as the present outdoor one? ; A.: No. You give no details as to height and length of your aerial, but the average "L" aerial has ‘very little, if any, directional effect. 8. Would it be better to run an outdoor aerial around the eaves of the house, insulating it at each corner? A.: No, because it would be in direct Yopposition to the first essential of a good Le, it must not run near earthed *bjects-such as guttering, downpipes, etc., oy, indeed, near any object at all. R M. (Waipawa): Is the "N.Z. Shortave wave Club Two" equal to or superior to any other set comprising detector and two audio stages? A.: Yes, we think it is quite equal to any such. set, 2. What is its: "B" consumption? .2. That, of course, depends upon the valves you use. If they are carefully chosen it need not be more than 8 mils. 5 HB (Napier) -You recommend the PT2 valve for the "Outspan." In an English magazine it says that by using the maximum voltage on the plate and screen it has an output of 500 milliwatts, and uses 12 miliamps. What alterations will ‘ba necessary in the "Outspan’" circuit to use the valve at its maximum output?

Band Secondary Reaction 9-16 24 4 15-30 54 7 28-55 84 11 50-110 154 15