Found in the February 1990 Radio Electronics issue, this sophisticated 100 MHz probe uses a period display module. The circuit has an external power supply.
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...