1. A REACTANCE AMPLIFIER COMPRISING IN COMBINATION A SOURCE OF A SIGNAL FREQUENCY; A SOURCE OF A PUMPING FREQUENCY; A CIRCUIT TUNED TO THE SIGNAL FREQUENCY; INPUT MEANS TO SUPPLY THE SIGNAL FREQUENCY INTO SAID TUNED CIRCUIT; A NON-LINEAR CAPACITOR, SAID CAPACITOR COMPRISING A FERROELECTRIC DIELECTRIC MATERIAL HAVING A TEMPERATURE REGION ABOVE ITS CURIE POINT IN WHICH A MAXIMUM OF NONLINEAR DIELECTRIC PROPERTIES ARE PROVIDED AND AT WHICH TEMPERATURE REGION THE DIELECTRIC MATERIAL CAN BE AUTOMATICALLY MAINTAINED BY INTERNAL DIELECTRIC LOSSES; SAID SOURCE OF PUMPING FREQUENCY BEING CONNECTED ACROSS SAID NON-LINEAR CAPACITOR FOR PERIODICALLY VARYING THE REACTANCE OF SAID CAPACITOR AND FOR DIELECTRICALLY HEATING SAID CAPACITOR TO SAID TEMPERATURE REGION WITH AN ALTERNATING CURRENT; COUPLING MEANS CONNECTING SAID TUNED CIRCUIT ACROSS SAID SOURCE OF PUMPING FREQUENCY AND SAID NON-LINEAR CAPACITOR; REGULATION MEANS DISPOSED BETWEEN SAID SOURCE OF PUMPING FREQUENCY AND SAID NONLINEAR CAPACITOR FOR ADJUSTING THE DIELECTRIC HEATING REGION OF SAID NONLINEAR CAPACITOR AND ALSO FOR ADJUSTING THE OUTPUT MAGNITUDE OF SAID SOURCE OF PUMPING FREQUENCY AND OUTPUT MEANS FOR DERIVING AMPLIFIED SIGNALS FROM SAID TUNED CIRCUIT.