14 to the addressed one of the power driver circuits for example driver 21 establishing the resonant oscillation across the transformer secondary the resulting reflected decrease of potential point b k is detected by the feedback network causing the potential at point d k to fall thereby continuing the action of the power driver circuit maintaining the current through the primary of the transformer and thus maintaining the oscillation for the entire period that the enable pulse is supplied to the oscillation circuit also the current flow through the primary of the transformer causes the quench clamp circuit associated with that stage to become disabled when the ringing in the transformer secondary reflects back to force the voltage at b k to rise the feedback network is no longer able to sink current and the potential at point c rises and providing that the initial pulse from the enable circuit to the driver has ended terminates the drive pulse the secondary continues to ring and when the ac component of the voltage at b k starts to decrease the feedback network begins to conduct forcing the potential at c to decrease producing another drive pulse the pattern is repeated as long as the externally applied enable signal.