This circuit is from a 1968 publication. Here we have several types of resistive sensors with individual adjustments triggering a single SCR. Power depends on the type of sound device to be triggered.
From a 90s Popular Electronics, this circuit emits pulsating signals for different types of...
Found in a Popular Electronics from the 90's, this circuit converts a 40 V symmetrical source to a 5...
This circuit generates frequencies determined by R3 and C1. We found it in the Radio Electronics magazine...