This circuit was found in a 1970 American publication. The FETs are power types according to the desired output current. The operational can be replaced for modern equivalents.
This basic Schmitt trigger was found in an American publication from 1968. The circuit uses...
This circuit is from an American 1964 documentation. Transistors of the time are used, but modern...
This simple circuit uses small speakers for both listening and speaking (microphone). The feeding is...