Found in a 1924 Gernsback publication this circuit uses 4 batteries for power and loop antenna. Listening is over a high-impedance type earphone or loudspeaker common at the time.
This circuit with different colored indicator LEDs has an expanded scale. We found it in the March...
This circuit can be used as an answering password system in a store, office, or other location....
This circuit is from the American magazine that no longer exists Science & Electronics,...