This circuit is from an American documentation from the 90's. The SCR can be of any type and the diodes must have current according to the controlled motor.
This circuit, from an old publication from the 1970s, can be made with silicon transistors like...
We find this circuit in documentation from the 1980s. The triac and diac are of conventional types...
The purpose of this circuit is to convert a short-lived pulse into a negative rectangular pulse. The...