This circuit was found in a 1970s American documentation. It can be applied to almost any regulator. The transistor used admits equivalent, depending on the circuit current.
This circuit has an interface for a multimeter or electronic voltmeter. We found it in a 90s...
This circuit was found in Radio Electronics from the 90s. Q3 must have a heatsink and R10 fixes...
This voice scrambler is used to obtain effects in the 2.5 to 5 kHz range. The circuit is from...