QUESTIONS AND ANSWERS

Radio Record, Volume V, Issue 24, 24 December 1931, Page 14

QUESTIONS AND ANSWERS

The Technical Editor will, through these columns, be pleased to help readers experiencing trouble with their sets. Queries are limited to three-for more than this a shilling fee is charged, and a similar fee is payable for queries answered by post. Supplying layouts. circuits and solutions of intricate theoretical problems is beyond the scope of this service. A coupon. must accompany all requests for information. Nonappearance of the coupon in any issue eannot be regarded as a reason for its not being used. * Address all queries, The Technical Editor, Box 1032, Wellington.

YF)YX26MC: Could the usual outdoor aerial be fitted in addition to the loop in the circuit of the Super Six? A.: Yes, but in doing so the set would | nial the fire underwriters’ regulaions. EGINNER (Wellington): Can a loudspeaker be used with a one-valve ‘eircuit? A.: Yes, but do you know your circuit is a violent oscillator? Use a fixed condenser in conjunction with your .0001 to .0003 in series with the aerial.

2. What type of valve should I use: A.: Use a high amplification valve of the A415 class with a four-volt accumulator or dry cells. How many turns should I have on the coils? A.: For a two-inch former and a 26 d.s.c. wire use 65 turns. Reaction 25 turns of 30 gauge, d.s.c. R R. (Gisborne) : Could six-volt valves * be used in lieu of two-volt valves for the Super Six without detrimentally affecting its performance? —

A.: Yes, they would be perfectly satisfactory, if not slightly better. VOLTAGE (Otago): Could the frame antenna described in the "Radio Record" of the 11th instant be suitable for a five-valve commercial set? A.: No; the aerial circuit has to he specially designed to take a frar2 aerial. G. (Nelson): Where could I obtain * full particulars regarding the construction cell charger, and how could these be combined to make one giving four volts? A.: For a 4-volts charger you would need to make up six Daniells cells as described in the "Radio Record" dated Nov. 7. P A.B. (Auck.): My set is of the * swinging coil type. Would I get better results if I pulled it to pieces and built a more modern two-valve set? T can get the Australians faintly. : It is questionable. Better results can be obtained usually by using newe) type valves. 2. Results are as good with the rheostat turned almost off as on. Is this detrimental to the "B" batteries? A.: No, it is to their advantage to work the rheostat back as far as possible, for by.so doing you are using less current than if it were turned up fully. 8. Please describe the following valves: P.610.-A six-volt Osram power valve 1o be used in the last stage. Medium 112, power-A power valve of the 610 class, but which takes a 7 of an amp. filament current. Ceco A-a 201A type of valve, fivevolt filament, + amp. current consumption. A general purpose valve. . 801A and C509A.-KHquivalents of a Ceco A (UX201A is the same valve). LP.6.-A six-volt power valve. Note: All the valves are fairly light on "B" battery consumption, the heaviest being P610, 112, and LP.6. } IWI (Auckland): Why can I pick up two stations on the same wavelength -one on 15 and the other on 18? In the daylight I receive the one that is usually on 13 on 18.

A.: It appears one station does hot keep on its proper wavelength at night. Check up with your neighbours and see if this is so, 2. Would a .0005 condenser be suitable for a wavetrap and what gauge of wire should I use with it? A.: It would be quite suitable if employed with a 2in. former, 26 d.s.c. wire, 65 turns. A H. (Devonport): Full details of the * broadeast coils for the Night Owl Three were published in last week's "RR." IGHTNING (Auckland): We cannot tell you very much unless you send us the circuit of your set. Apparently a wrong connection has been made. Mu (Khandallah): The fact that when you move your detector you cause the frying noise to stop, points to one of two things being wrong with your set. First a defect in a socket or a loosé connection to it, or a defective valve. If you cannot track both these faults down your wisest plan would be to get a radio serviceman to inspect your set. M H.O. (Temuka): Can I use a .00085 * and a .0005 condenser for the Eagle Five? A.: If you use a .0005 condenser you will need to wind about 10 less turns on the coil, otherwise it will be quite suitable if you use it in conjunction with a .00035. It is immaterial which stage you use it in, 2. Would two S625 valves be suitable for the s.g. detector of the ‘Kestrel Three’?

A.: We should imagine them to be, but of course have not tried them. We are always a little dubious of things we do not try. C D, (Christchurch) : I have construct- * ed the "B" accumulator as per the 1930 "Guide," but find its capacity is very low indeed. A.: The plates you sent appear quite normal for unformed plates, but do not appear to have had any charge. The trouble appears to be the charging yoltage, which may not have sufficient extra voltage above that of the cells to charge them fully. The hydrometer reading 1s about right for cells with only a small charge. The original of this battery has been running for two years with distilled water added when required, and charges in series in about 10 hours at 60ma. Do both of the parallel halves charge up equally? In parallel charging, especially in large groups, such as 100 volts, there is always the risk of one half having a higher resistance than the other, and consequently it will receive less charge and run down early when in use. The remedy for this is to have a variable resistance 2 circuit with the block of least resist‘ance, and adjust until each block is passing equal current. When charging in parallel, always break the parallel connection between groups before cutting off the charging current. A CORRESPONDENT, whose coupon hag gone astray, and whose name was not on his letter, states that he has built a second audio on the "Night Hawk," but gets the Australians only faintly on the phones, but he can_ put Siberia and Indo-China on the speaker. A.: You must realise that the broadcast

function of the "Night Hawk’ 1S omy 4 compromise unless the coils are made on in. formers. Other than that, it might be as well to bear in mind that the Australian stations at the present time are very weak indeed. 2. 1 had to put about 70 turns on the reaction condenser to make the set oscillate. A.: This is not altogether unusual. We ‘presume you were using a fairly smallsized reaction condenser, or that ‘you hada valve which was not a good oscillator, Use a PM8, not a PM4. in the first audio socket. Your B406 is g last stage valve, and with 90 volts should carry about 12 volts bias. We are pleased to hear that you have