Questions and Answers

Radio Record, Volume VI, Issue 33, 24 February 1933, Page 21

Questions and Answers

ed. H, (Inglewood): Could you give me the circuit constants of the six-watt amplifier described in the 1932 "Radio Guide"? A.: They are all contained in the diagrams and the article. A suitable powerpack is described on page 111, or you could build the one described in the 1931 "Radio Guide." ALVE" (Ashburton) : At present the set is using the original valves, which are a mixture of three different makes. Should I keep to these or use just one make only? : Use one make only, Any one of the thtee you mention. \ G R.G. (Westport): Could you advise me as to a suitable text-book .to study for the radio serviceman’s examinaion ? A.: A book which will give you an excellent working knowledge of radio and which is to cover the, complete syllabus will be published in about a month. 2. Where could I obtain full particulars of the exam.? A.: From the registrar of the examination board, 8 The Terrace, Wellington. 3. Could you describe in the "R.T." an 8-valve superhet. using the 234, 232, and 230 valves and "B" class amplification ? A.: We have had a set sueh as this in view for some time, though we can make no promises as to when it will be described.

iJ. R.G. (Thames): What short-wave adaptor could be used with my set? : The manufacturers of the set you are sell an excéllent and reasonablypriced short-wave adaptor. 2. The set functions well for a few minutes ‘and then the volume suddenly dies away, becoming almost inaudible for yarying periods. Then, with a click, volume returns to normal. Is this due tointerference or is the set at fault? A.: The set. Have you had your valves tested recently? It appears that at least one of them ig defective. G L. (Inglewood): I replaced my two * 245’s with 247’s, as recommended by you, and the set is now going all right. When first connected up it oscillated, and after various experiments I cured this by connecting two -.006 condensers from the grids to the 247’s to earth. Is there a better way of stopping oscillatien? A.: Yes. To start with, the value of theycondensers you are using is much too hig and high note loss would be serious.

‘| Try connecting a 100,000 ohms resistor between each of the grids and the two "G’s" on the transformer. If this does not cure the trouble, connect a .00025 mfd. fixed condenser from each grid to earth. J R.A. (Dunedin): Could you recom- * .mend a simple five-valve battery circuit employing a screen-gird valve? A.: Yes, the "De Luxe Five," described in the February "Radio Times," is the very set you want, "PUPS" (Auckland) : The 1931 "Radio Guide" is still procurable, price 2/6, posted 2/10. The gauges of the wire you enclose are as. follows: Fine enamelled, 386; black enamelled, 28; cotton covered, 24; silk covered, 30, H W. (Tareora): I have a three-valve * battery set, and recently I had the A battery charged. I can now hear Christchurch only very faintly, but Auckland and Wellington come in very well at their usual] strength, My B battery is five months old. A.: In all probability your B battery is slightly flat, and this is first apparent on the weaker stations. "EXAR NORTH" (Auckland): T have a six-valve American set with the theostat working on the three r.f. valves. With the rheostat full on I can increase the signal strength from weak stations by putting my hand close to the detector yalve, Why is this? 2"

A.: It is duieult to say. Lnere snoulic be a fixed condenser of value .001 mfd. across the primary of the first audio transformer or from P of the detector socket to A- or earth. Without this condenser, signals would be weak and could very likely be improved by placing your hand near the detector, 2 The rheostat has a pair of points on the back similar to the cut-out of a ear generator, Normally these are open, but sometimes they will come together, and when they close the ordinary switch takes no effect, and I have to turn the rheostat back the full turn to separate the points. What are these points for? A.: We don’t know, Are you sure your rheostat is connected the right way round? 3. Could 1 expect better ‘results with the "Outspan Four" or the "De Luxe vive"? Which of these is the best for dx? | Av: The "Outspan Four."

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