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 is from a 1968 documentation using one of the first integrated circuits available at the...
This circuit appears elsewhere on this site. This is from an American 80's circuit manual....
This circuit consists of an inverter powered by only 4.5 V. The circuit is from a 1967 Mullard...