This 555-based circuit was obtained from the 1995 Encyclopedia of Electronic Circuits volume 5. It triggers an SCR when the transistor is cut off.
This Japanese radio is from the 60s, presenting excellent sensitivity and an output power of 100mW...
Found in a Popular Electronics from the 90s, this circuit uses components that are still current....
This circuit consists of a simple capacitance bridge. The handset can be high impedance from 500...