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.
This is one of the possible configurations using the LM139, 239 or 339 voltage comparators. The...
Have you not yet memorized the color code used to identify resistors and capacitors? Do you have...
Found in American documentation from the 90's, this circuit consists of a solid state relay with...