Found in a Raytheon transistor manual from the 1950s, this circuit uses one of the first commercially available transistors, the CK722. The circuit is for using a small speaker as a microphone.
If you are on an old PC that you use for experiments, control or other applications, this circuit is...
We found this circuit in an American publication from 1977. The circuit drives two LEDs according to...
In this circuit, the integrated amplifier used is uncommon today. The circuit is from an American...