This blocking oscillator configuration was found in a 1964 American book. The circuit can be designed with modern transistors and the frequency depends on the transformer.
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...