In this circuit of an American documentation of the 90s, when the light is cut, we have the production of a pulsating tone. R3 determines the trigger sensitivity.
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...