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.
The sensors can be screens having porous tissue between them. When the water moistens them, the...
This circuit, with the TBA810 circuit, which is no longer common today, was found in a 1985...
This circuit with neon lamp and unijunction was found in the September 1970 Radio Electronics...