Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
This two-transistor constant current source is from a 1968 documentation. Modern equivalent...
This circuit was obtained in a 1977 technical documentation. The PUT admits equivalent and the...
We found this circuit in a 1997 documentation. Its purpose is to turn a load on or off using...