Discussion on "High Audio Power from Relatively Small Tubes" - Loy E. Barton

The discussor feels this paper (ibid., vol 19, pp 1131-1150, July, 1931) commends itself to a large part of the radio engineering field. It is of special importance to engineers concernedwith the development of transmitters. The paper should be read by everyone who contemplates developing apparatus in which power efficiency of the radio equipment is important. Push-pull amplifiers have been used in communication circuits for many years. They have usually been employed for reduction in distortion, or for providing a balanced circuit arrangement. Barton's paper emphasizes a long neglected use which results in increased output power, and decreased dissipated power simultaneously. This is accomplished by using a separate tube to amplify each half of the audio wave. This circuit instantly commends itself to those interested in audio-frequency power at high power levels. The operation of loud speakers will probably occur to us as its widest field of application, but a very important field also exists in connection with radio transmitters. It is the latter application that is discussed further, ie that in transmitters employing plate circuit modulation of the power tubes, the over-all power efficiency is brought to a relatively low value by the power consumed in the modulators. By embodying push-pull modulator tubes, with a bias which is very close to the cut-off point, the power consumed in the modulators is almost eliminated during quiescent periods, while during talking periods the efficiency of the modulators is more than doubled. The improvement in efficiency in the modulators, therefore, has the very important effect of raising the plate circuit efficiency of the transmitter to a value double that of the next best system.