This 4-tube circuit was found on a Radio Craft from December 1945. The circuit has excellent sensitivity. Power comes from a power supply with a transformer.
This circuit was found in the July 1992 issue of Radio Electronics magazine. The circuit is based...
This timer activates a relay after a time interval of up to 15 minutes has elapsed, starting from...
The circuit presented is based on a mechanical tuning fork. The circuit is suggested by National...