Crystal Corner

Radio Record, Volume II, Issue 43, 10 May 1929, Page 31

Crystal Corner

The Crystal and Valve. "H).T.D." (Lower Hutt) has constructed this receiver, and has had good results on the loudspeaker 2YA, and on ’phones 1YA, 3YA, 4YA, 2ZF, 2ZM, 2FC, 2BL, 38AR, and 2GB, and many others whose call-signs are difficult to catch. Now, however, he states, the receiver will oscillate for a few seconds and only on a small portion of the dial. Both the "A" and "B" batteries are only’ three months old, and with the last "B" battery the set would oscillate freely with 8 volts.on the plate, A.: The "A" batteries are, no doubt, run down, for a detector will oscillate with very low voltage on the plate, but the filament voltage must be up to full strength, or thereabouts. Try new "A" batteries, and see the result. ; My valve has been in use for nine months. Is it falling off in efficiency? If so, what make of 2-volt valve do you recommend for this circuit? A.: It is unlikely that the efficiency of the valve is impaired through its use. In any case, it should be tested by a dealer. The make of valve is a good one, and we could not recommend a better. Can two 13-volt batteries be used with a 2-volt valve, controlled by a 8 ohm resistance? A.: Yes, but when the batteries are new do not turn the rheostat on full. What is the cause of "blind spots" on a part of the dial, and what is the. remedy?

A.: The cause: is that the aerial, which has its own natural frequency, becomes tuned in resonance with the set and alters its tuning. The batteries, too, may. have an effect in this direction.. Try a small fixed con-denser-.00025, say, in the aerial circuit, but see "Questions and Answers." ANOTHER correspondent, "W.B.." has had difficulty with the three-in-one. When the output of the crystal is joined to P, of the transformer, he can hear nothing. He asserts that the wiring has been tested. by a radio dealer, and no mistakes found. He asks how another stage may be added. , A.: It is extremely difficult to state thre gh the columns where a mistake may be found, when the receiver itself has been checked by a dealer and ‘said to be O.K. One can only suggest that the valve is at fault, or may be the transformer. These should be tested. Another stage may be added as described for the "Combination" receiver this week. Failure of Carborundum, "L.A. (Christchurch) has not had satisfaction with the carborundum. It would not work on his set, while when tested on a. neighbouring set it proved O.K. Tried again on his own set, it refused to function. A.: This type of crystal sometimes requires rough treatment. Give it a sharp jar and then try. Also try reversing it in the holder.