This is an interesting configuration of the LM317 voltage regulator found in an EDN from the 90s. The circuit uses an optical coupler and is intended to supply constant current to a sensor resistor.
Found in a 1970 American publication, this circuit uses transistors of the time. These transistors...
This emergency lighting circuit includes a small inverter for a small fluorescent lamp. The...
This circuit for a 455 kHz ceramic filter was found in the October 1952 Radio Electronics...