This circuit uses a crystal phone and can be built with more modern transistors like the BC548. The original circuit is from a 1979 publication and is powered with only two AA or AAA batteries.
This circuit is from a Radio Electronics from June 1964. The bridge diodes must be in accordance with...
The frequency range of this circuit depends on the transistors used. The circuit is from a Radio...
This circuit was found in an American audio documentation from 1968. The configuration can be...