Audio amplifier with reduced plate dissipation

Abstract

An audio frequency amplifier arrangement is described which results in decreased plate dissipation. The arrangement is suitable for either class A or class B amplifiers. The scheme employed is to feed the grid of the amplifier an auxiliary signal as well as the desired audio frequency signal. The auxiliary signal is at a super-audible frequency and is automatically adjusted so that its peaks in the positive direction never cause the peak plate current to exceed the maximum current peak of the desired signal, nor shall its amplitude be so high as to cause clipping of the auxiliary signal on its negative peaks; in other words, the added wave should not affect the average value of the current generated by the desired signal. The plate circuit has its regular low-frequency load, but it also has a load circuit tuned to the super-audible frequency. The super-audible output may be dissipated as heat in a resistor. Calculations have been made which show that for a given input and output at low frequencies, the maximum plate dissipation of a class A amplifier may be reduced to as low as 41 per cent of the maximum dissipation attained in conventional class A operation, and that the maximum plate dissipation of a class B amplifier may be reduced to as low as 50 per cent of the maximum dissipation attained in conventional class B operation.