In the figure we have the configuration of a voltage regulator with 3 transistors. The components depend on the desired voltage and current as well as on the characteristics of the transistors.
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...