This simple sensitive circuit was suggested in a July 1992 Radio Electronics issue. The relay is a double-contact changeover relay. Sensitivity adjustment is made at R2.
This circuit is from a 1967 General Electric SCR manual. The capacitors are polyester and the...
This oscillator for frequencies up to a few tens of kilohertz was found in a 1970s documentation. The...
This varicap-less modulator circuit was found in an Electronic Design from the 90's. The circuit...