This circuit was found in a 1966 General Electric documentation. It makes use of direct contact water sensors and therefore requires an isolation or low voltage relay drive transformer.
Published in Popular Electronics with the curious name of Obnoxious Noisemaker, this 1968 circuit...
This preamplifier circuit for turntable cartridges was found in the March 1994 issue of...
E) This circuit was found in documentation from the 1980s. The integrated circuit used is not very...