This circuit uses two relays that switch when the voltage exceeds the value given by zener D2. The circuit is from a Radio Electronics magazine from April 1975.
This circuit from a June 1957 Radio Electgronics is for oscilloscopes of the time with a maximum...
This simple receiver for listening on a crystal phone tunes the range of medium waves. The circuit...
This circuit in a receiver that allows the capture of distant stations with short waves. The...