The selected circuit was found in GE's 1977 semiconductor manual. 3N84 is a controlled silicon switch and SCRs support equivalents. The transistor can be a BC558, depending on the supply voltage.
This simple voltage regulator with FET was found in American documentation from the 1980s....
In the figure we have the trip circuit for a relay with audio signals. The circuit is from an 80's...
Common general purpose silicon diodes when direct biased provide a voltage fall of about 0.6 to...