This simple circuit is a continuity test that, in addition to testing resistors, can also test other components. Power is provided by batteries and the LED can be of any color.
This drain dip oscillator was found in an old English documentation. The JFET can be of any type...
This SCS counter circuit was found in a 1964 General Electric documentation. The circuit has a...
This is the circuit of a commercial radio from the 60s, sold in Japan. The circuit shows the...