We found this circuit in the April 1978 issue of Radio Electronics magazine. The power supply must be symmetrical, and the maximum recommended frequency is around 10MHz.
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...