H.F. Amplification

Radio Record, Volume II, Issue 25, 4 January 1929, Page 27

H.F. Amplification

IX H.F. stages many experimenters use a high value of H.T. voltage

without a biasing battery, and whilst this may result in a considerbale degree of amplification in some cases, it is wastful of H.T. battery current, and does not usually produce the best tone quality. Reducing this H.T. voltage will obviously have the effect of saving H.T. battery current, and will frequently be found to improve the tone quality on stations not too far distant. A still better method, of course, is to introduce a suitable value of grid-bias voltage, which has the effect of improving the quality very greatly and at the same time cutting down the H.T. current. In an actual test two H.F. amplifiers consumed 12 milliamperes in the plate circuit when the H.T. voltage was 90 volts; the H.T. current consumption dropped to 7 milliamperes for the two valves at an H.T. voltage of 66 volts and to 3.4 milliamps when the H.T. voltage was reduced to 45 volts.