In the figure we have the configuration of series regulator protector suggested by Motorola in 1968 documentation. The transistors are of the time, being able to be used modern equivalents.
This basic configuration can be found in a lot of articles on this site. In this case, the relay...
This circuit is from American documentation from the 1980s. The transistors are general purpose...
The circuit is simple, as it uses only one transistor and a relay that can be MC2RC1 or MC2RC2,...