This circuit is from a 1924 book by Gernsback. The receiver uses two tubes and listens to headphones. Power is supplied by battery with the indicated voltages.
Found on 90's Popular Electronics, this circuit triggers when the microphone picks up a sound. The...
This circuit, which we found in an Argentine publication from the 1970s, uses a large high voltage...
Found in a Popular Electronics from the 90s, this circuit generates signals from 2 Hz to 30 kHz in...