Found in a 1924 book by Gernsback, this circuit uses a double variable capacitor, a component not very common at the time. Listening was done on a loudspeaker at the time.
This oscillator for testing resonant circuits was found in a Radio Electronics magazine from June...
This circuit, suggested by an old American publication, allows you to use the AM radio antenna of a...
This circuit limits (clip) the intensity of a signal, according to the setting of P. The circuit is...