This circuit is from a 1968 Motorola power circuit manual. The circuit uses transistors of the time. The passing band is 45 Hz to 100 kHz.
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...