This circuit was found in the 1969 RCA thyristor manual. The circuit has a limiter (clipping) with two 12 V zener diodes in opposition to cut power grid pulses that may influence the trigger.
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...