This is the Gates Radio Section of
The Broadcast Archive

The FM20H3 and later FM20K series had an underdrive relay. They found the tuned circuit in the driver and installed a relay that would pull in with drive from the TE-1. The relay was in the interlock circuitry of the plate supply. If the TE-1 exciter went off frequency the voltage at the tuned circuit would drop out the relay as the exciter went up or down away from operating frequency off went the plate voltage. Sometimes it would come back on frequency and the plates would come back on and then drift off again. In the early models of the 20 kW. before the under drive relay, when the

TE-1 would go off frequency the PA would heat up until the components broke down. The trombone tuning section would all have to be replaced.