Using the name of varactor this circuit was found in the Radio Electronics magazine of July 1982. Varicaps of any type can be used and the components selected according to the component.
This small commercial radio for the MW band with germanium transistors was found in Japanese...
This alarm has a trip system with an LED on a keyring. The sensor is hidden by the glass or...
This circuit turns off when switch S1 is opened. The circuit is from the 1989 Radio Electronics...