dk is connected between junction k and the base of a transistor qk which zener diode has its cathode connected to junction k transistor qk has its emitter connected to bus bar y and its collector connected to junction j through a resistor rjk a secondary winding ts of transformer t is connected between bus bar y and the base of a transistor q whose emitter and collector are connected to bus bar y and the base of transistor qy respectively a resistor means rq is connected between the base and the emitter of transistor q the operation of the circuit of fig1 may be explained as follows the two transistors qx and qy are operated as a self oscillating half bridge inverter a with timed positive current feedback being provided by saturable feedback transformers tx and ty b with b power being provided from a center tapped dc power supply which power supply consists of ac power source s rectifier means r and series connected filter capacitors cx and cy which capacitors are of substantially equal capacitance and connected together at junction z to form a power supply center tap and c with circuit oscillation being initiated by way of the trigger sub circuit consisting of resistor rj which charges capacitor cj from b and which capacitor is periodically discharged into the base terminal of transistor qy by way of diac dj the time it takes for the circuit to be triggered into oscillation is determined by the time it takes to provide the first trigger pulse to.