1. A SAFETY DEVICE FOR PROTECTING A MAGNETIC AMPLIFIER POWER SUPPLY SYSTEM FROM EXCESSIVE VOLTAGES COMPRISING A MAGNETIC AMPLIFIER HAVING INPUT AND OUTPUT CIRCUIT MEANS, A RECTIFIER HAVING ONE TERMINAL CONNECTED IN SERIES WITH ONE TERMINAL OF SAID INPUT CIRCUIT AND POLED TO BLOCK THE OUTPUT CURRENT FROM PASSING THERTHROUGH, A SOURCE OF INTPUT CURRENT HAVING ONE TERMINAL CONNECTED TO THE OTHER TERMINAL OF SAID RECTIFIER AND A SECOND TERMINAL CONNECTED TO ONE TERMINAL OF SAID INPUT CIRCUIT, SAID ONE TERMINAL OF SAID RECTIFIER HAVING A FURTHER CONNECTION TO THE OTHER TERMINAL OF SAID INPUT CIRCUIT AND POLED TO PERMIT INPUT CURRENT TO PASS THERETHROUGH, SAID OUTPUT CIRCUIT AND RECTIFIER MEANS BEING BLOCKED UPON INTERRUPTION OF SAID INPUT CURRENT.