RADIO REPLIES

NZ Truth, Issue 1108, 24 February 1927, Page 2

RADIO REPLIES

Q.: I have a straight - 3-valve receiver (Det and 2L.F) employing reaction, and am troubled with the* following: - - .-■-■' (1) Reception can .only be obtained w)ien reaction is brought to oscillation point and- then the music, etc., is consequently distorted and set; causing in-, terf erence. I have tried different sizes of reaction coil, also reducing "B" battery without any improvement. 'If second transformer is faulty (which I have reason to believe is so) would it cause above trouble? (2) When filaments are lighted, a high droning musical sound of constant pitch is heard from the speaker. This does not alter m pitch when any variation of rheostats, condensers, coils, etc., are made. Neither does it alter when aerial and earth are disconnected.—"T.W." (Timaru). A.: (1) No, I do not think your trouble is due to your second transformer. The trouble ilies m the aerial-grid-reaction circuit. If, when you reduce the "B" battery current simultaneously with the "A" battery. current and the distortion is still present you must look further afield for the trouble. Make sure that your A and B batteries, are showing correct readings. . Try reversing the reaction coil leads and notice if there is any improvement then. Jf not different values of grid leaks should be tried. (2) Tour trouble here is* m. the two audio transformers. They, . are most probably inter-acting against each other due to their being side by side. They should be -placed some, distance apart with their windings at right angles to each other, and all wires well spaced apart. If this does" not cause the howling to cease try changing 'the leads from one or more of the primary windings of the transformers./ ■ ,:■ v Finally, both iron pores of the transformers should be "earthed.".