Found in a 1964 Electronic Design, this circuit makes use of period components. The components are from the time, and modern equivalents can be used.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...