We found this circuit in an American documentation from 1947. The circuit uses 5 tubes and has a feature to keep the tube filaments preheated.
Using an optocoupler this circuit turns on the light in a bedroom for a set amount of time when...
This basic voltage comparator circuit has a reference voltage given by a zener diode. The input...
Found in a Hands On Electronics of the 80s, this circuit makes use of a gas sensor of the time....