This very complex circuit in terms of the number of transistors was found in Radio Electronics from March 1966. The circuit is for low impedance headphones. The transistors are from the time.
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...