Questions and Answers

Radio Record, Volume IV, Issue 25, 2 January 1931, Page 14

Questions and Answers

FE. 2- (Auckland): Will you design * coils for the P.OJ. Four using -0001 condensers. A.: Such specifications would. take some time to work. out. We will be publishing a very complete table in the near future. , .

G S. (Westport): I have an American * set using 5 201A’s and a 112 in the last stage. Could I use a 5 221’s and a 171 in the last stage? A.: The 221’s would be a good proposition though their price has recently gone up considerably, and it may not be worth the extra outlay. The 171 would probably be a disadvantage in that it would drop volume without adequately compensating in tone. If you use a power valve of the B605 type you would get the best results. , (CARLO (Palmerston North): I cannot get the results that I should do, although I have a good aerial and earth system. Would it be an improvement to use 7/029 instead of 7/22 wire?. A.: The two are the one and same wire. 029 being the diameter of the.22 gauge wire. If you cannot get the stations in well we should advise having the screen grid valves tested or borrowing a new screen grid valve and trying it in all the sock: ets and see if there is any difference From your specifications there is nothing wrong with either the aerial or the eartn system. C A.H. (Napier): Would a. five-valye * sereen grid B.D. be sufficient to work a dynamic speaker? A.: That denends upon the plate voltage used in the last stage. You would peed 135 or preferably 150 for satisfactery results. 2, Would an inductor dynamie speaker be better? A.: Yes, especially if: you are in a locality where electric power is not available the inductér dynamic would be preferable. OFTY (Christchurch): I eannot buck the hum out of my 1. W. A.: This seems like. trouble in the grid bias chain. See: that the grid leak resistances are all the correct value and that in no case is there an open circuit Carefully inspect your valve holders to see that they are making proper contact and watch the points where the re. sistances join the aluminium sub-pane: 2. I put the power pack and the condensers underneath the sub-panel. Would this cause a hum?-No. 8. I found volume was better when the pick-up is inserted in the cathode. A.: Our experience was the opposite; it was better when the grid return was broken, 4. I had to put a condenser and grid leak in the earth lead to get any vyolume, A.: Probably one of your resistances is shorting out and you cannot operate the earth potential as you should do. RAPATA (Auckland): Can you elaborate upon the sketch of the valve tester given in the Radio: Guide?

A,: Yes. Further particulars hav: been prepared and if there is not space in this issue they will appear in the next. QPSOx (Pio Pio): Would a screen grid circuit with the new Osram p42 in the last stage be a good one foi all- rere work ? : It should do for the valve comis good. 2. Would it be superior to the H.R. for broadcast? A.: To the H.R, using a triode valve as RF. yes. 3. Do you know of a better set? A.: We cannot compare it with any other: set of its type until we have seen a cireuit. You should be interested in the new B.D. which will be in either the "RR." or the 19381 "Guide." D S. (Market Cross). Which is the * better of two amplifiers, one using a 112 followed by one 171A and two 245’s, or (b) three stages transformer coupled using two LS5’s and four LS5A’s. A: "A" would be the better, but neither are particularly good. Quite.a good amplifier for a dance hall would be one 221 coupled-to two 221’s in pushpull in turn transformer coupled to two LS5A's. providing good transformers were used and high voltage this qutfit would give splendid quality. The 50-watt type olf L.w. amplifier. would also suit your purpose if you have a.c. available. It was described in the May issue of "Radio News." . IRELESS (Invercargill). — Where would I put the tapping in the aerial eoil of a one-valve receiver? A.: The particular points are not very important so long as there are, say, five of them evenly distributed through the coil. You could then tap on to the one that suits your purpose best. HELBARN (Auckland).-I have had a great deal of trouble with my factory- B.D. set, and now the s.g. valve will not work properly. : As your set has been in the hands of a dealer several times, we really cannot do anything to help you. Probably it would be better to take it or send it to Ay B.D. specialist. Will the Loftin Four give plenty of and quality, and will it excel a good push-pull amplifier employing 245 valves? A.: The Loftin White should be the better. It will give a greater pickup, and has certainly a better tone. 3. Will my set work a pickup satisfae- torily?

A.: You really need. push-pull to get satisfaction from stamophone reproductions,