This circuit with 1% regulation aims at replacing mercury cells. We found it in a 1967 documentation. Transistors can be replaced with modern equivalents.
Found in a 1966’s General Electric documentation, this circuit uses a triple diode from the time....
Found in documentation from the 1990s, this circuit converts 12 V to 9 V from a car's power...
This ohmmeter can be made with a scrap milliammeter used for continuity tests or even resistance...