This circuit uses a capacitor that depends on the frequency of the crystal. We found it in a 1967 documentation. The maximum frequency is around 100 kHz.
This circuit is from an American 1964 documentation. Transistors of the time are used, but modern...
This protection circuit for battery chargers was found in an old Elektor. The relay is according to...
Found in an Electronics Now from the 90s, this circuit is used to control the supply of...