The setting of this power supply is only 0.1%. We found it in a 1969 US documentation. Transistors may be current equivalents. Note the use of symmetrical power supply.
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...