This circuit is from a 1980s Motorola documentation. The circuit makes use of old components that can in some cases be exchanged for modern equivalents.
The sensor of this circuit is a common transistor and the trigger point is set on the trimpot or...
This circuit was found in a 80’s Popular Electronics. The components are common and the 8-ohm...
This circuit is from an English publication from 1976 but can be easily assembled with BC548...