The Thyristor Firing Unit is a plug-in control module designed for the control of power thyristors in power converter circuits. It generates four 0-5 V pulse signals in the single-phase control mode, and six in the 3-phase mode. These control or “firing” signals are brought out to a 9-pin socket and can be routed to the Power Thyristors, Model 8841, through the use of an included mating 9-pin socket. The firing angle is determined by a low-level dc signal applied at the angle control input. The dc source output on the front panel can be used to produce this control signal. Four conversion functions can be selected to change the direction, and the rate of change of the firing angle which can be easily monitored on a 7-segment display on the front panel. A synchronization signal from the ac network is applied at safety 4 mm sockets.