This circuit was found in an American documentation from 1969. Indications of the used transistors are not given, but general-purpose types can be tested.
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...