This circuit was found in a 90s Popular Electronics. It produces a muted tone similar to that produced by a bell. The signal must be applied to an amplifier.
This circuit was obtained from Dutch documentation from 1964. The components are of the time, but...
This static switch circuit or solid-state contactor was found in a Motorola documentation from...
This control for bass, midrange, and treble was found in the March 1995 issue of Electronics Now...