HV Step Start and Blower Delay Control
 

The High Voltage Step Start is a simple circuit made up of RY2, R57, D1 and C2. When the HV control relay, RY1, is energized by the triode control board, the 240 VAC is rectified by D1 and applied to RY2. C2 and R57 filter and limit the current and voltage to the relay and the time it takes C2 to charge provides a time delay for energizing RY2 which applies the full voltage to the plate transformer.

The Blower Delay is provided by SW1 thermal switch, attached to R55 with epoxy. R55 gets hot when the power is applied and causes SW1 to close. When the power is removed, SW1 remains closed and allows the blower to continue running until R55 cools and SW1 opens.

RY1 provides the primary HV control from the triode control board.