Found in an American circuit manual from the 1970s, this circuit can use any general-purpose transistor. The operating frequency range is from 600 to 4000 Hz.
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...