This circuit was found in an English publication from 1967. The circuit is for listening on a phone. Transistors are types of germanium of the time.
We find this circuit in a radio amateur publication of 1977. Its purpose is to measure the...
This circuit was obtained in an old US 1974 documentation when Nixie tube displays were common. The...
This ultra-low consumption circuit was originally designed to be powered by a solar panel or small...