We found this good amplifier in a Japanese publication of 1966. Transformers are uncommon nowadays and the power supply is included. Power is a few watts.
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...