This circuit from July 1975 Radio Electronics uses any operating system with a symmetrical source. The waveform is shown on the side of the diagram.
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...