Transistor demodulator for high-performance magnetic amplifiers in A-C servo applications

FULL-WAVE magnetic amplifiers are not efficiently controlled with a-c signals applied directly to the control windings because the circuit configurations necessary do not give sufficiently high gain. Half-wave magnetic amplifiers which can accept a-c signals directly have relatively low gain. The most sensitive, stable magnetic amplifiers require a d-c control current, but in many servo applications the servo amplifier must accept a phase-reversible alternating voltage and deliver an output that will reverse phase as the phase of the input signal reverses.