This circuit triggers in 100 microseconds in case of excess voltage. The adjustment is made in the pot. The circuit was found in 1969 documentation.
The circuit shown is from an old European publication. In it we have the way to activate a relay...
We found this circuit in a European publication from the 1990s. Transistors are still common types...
This circuit was found in an American documentation and can be added to common amplifiers of any...