This is an amplifier circuit intended for modulating transmitters. The 5-tube circuit is from an American manual from 1947. The power supply uses a transformer.
This circuit simulates an inductor. Or operational amplifier of old type, but a configuration is...
This circuit for the logic control of the 555 in a power supply was found in the October 1989...
This traditional configuration from a 1980 publication shows how a reed relay is used to control a 240...