We found this circuit in a documentation for radio amateurs from the 70s. The transistors can be the BC548. With it, small speakers of 4 or 8 ohms can be used as microphones.
Suggested by an American documentation for 1969 neon lamps, this circuit provides SCR control with...
This symmetrical source was obtained from Popular Electronics from February 1979. Transistor Q1...
The transistor may be any general purpose, but the integrated transistor is not common today....