This sensitive circuit was found in the August 1971 issue of Radio Electronics magazine. The SCR is equivalent, and the transistor may be a BC548. The load may be a relay.
Microphones and other signal sources can be connected at the input of this circuit, with the 4.7...
This 741 operational circuit can be found with slight variations in this section and on this site....
This is another sampling and holding circuit found in a factory manual from the 1980s. The circuit...