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 can be used for several purposes such as pulse counter, pass counter, roulette, etc....
This circuit is from Radio Electronics. The magazine no more exists, but the circuit can be...
We found this circuit in a French documentation from the 80's. The components used are still...