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 was found in a Popular Electronics from the 90s. The power source must be symmetrical...
In the figure we have a circuit to excite a piezoelectric capsule taking advantage of its resonant...
The circuits below were found in amarican publication of the year 1958. The transistors are...