This circuit was found in Motorola documentation from 1966. The lamps are according to power and current according to the components used which are uncommon today.
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...