1. IN A MAGNETIC AMPLIFIER HAVING AN INPUT CIRCUIT, AN OUTPUT CIRCUIT, A CONTROL REACTOR AND A DIODE; SAID CONTROL REACTOR HAVING A MAGNETIC CORE; SAID MAGNETIC CORE HAVING A MAIN WINDING AND A CONTROL WINDING WOUND THEREON; SAID INPUT CIRCUIT, SAID MAIN WINDING, SAID DIODES, AND SAID OUTPUT CIRCUIT BEING CONNECTED IN SERIES; A CONTROL CIRCUIT CONNECTED TO SAID CONTROL WINDING FOR SUPPLYING A GIVEN NUMBER OF VOLT SECONDS TO SAID CONTROL WINDING DURING THE TIME SAID DIODE BLOCKS CURRENT FLOW BETWEEN SAID INPUT CIRCUIT AND SAID OUTPUT CIRCUIT; SAID GIVEN NUMBER OF VOLT SECONDS BEING UNCHANGED BY THE CHARACTERISTICS OF SAID CONTROL REACTOR AND SAID DIODE; SAID CONTROL CIRCUIT INCLUDING AN AUXILIARY A.-C. VOLTAGE SOURCE AND AN ADJUSTABLE IMPEDANCE MEANS CONNECTED IN CLOSED SERIES RELATION WITH SAID CONTROL WINDING; SAID GIVEN VOLTAGE OF SAID AUXILIARY SOURCE BEING IN A DIRECTION TO DRIVE THE FLUX OF SAID CORE TO A GIVEN VALUE LESS THAN SATURATION, AND IN A DIRECTION OPPOSITE TO THE DIRECTION OF FLUX CHANGE CAUSED BY FORWARD CONDUCTION CURRENT THROUGH SAID DIODE AND SAID MAIN WINDING; SAID FLUX OF SAID REACTOR CORE BEING CHANGED FROM SAID GIVEN VALUE TO A SATURATED CONDITION WHEN CURRENT FLOWS THROUGH SAID DIODE IN THE CONDUCTION DIRECTION OF SAID DIODE.