a current control circuit that employs a magnetic amplifier and an active feedback circuit . the feedback circuit establishes the effective operating current of the amplifier at a fixed point . the magnetic amplifier includes a pair of oppositely wound gate windings , a bias winding and a control winding . the gate windings are driven by an oscillator driver that generates a gate winding current and a gate winding voltage . a reference voltage and the gate winding voltage are applied to a feedback amplifier and the feedback circuit . when the gate winding voltage becomes equal to the reference voltage , the feedback circuit is stable and the gate winding current is set to a desired zero current operating point .