This circuit is from an old Electroics Now. Its purpose is to protect the fax and modem lines of two computers of the time. Suppressors are types of the time.
This circuit is from an English magazine of 1977. The circuit is still current, just using BC547...
The adjustment of the maximum load voltage is made in the trimpot. The circuit is from 1994...
In the figure we have the conventional configuration of a differential amplifier with the...