Found in an American publication of 1968, this circuit makes use of a pilot light of the time. It can be replaced with LED with appropriate series resistor. Transistors may be modern equivalents.
Found in the 1965 Radio Shack documentation, this short-range AM circuit can be built with...
This circuit was found in a 1980s documentation. It is intended for remote vibration monitoring...
This circuit can be found on this website in similar versions. The power supply is given in...