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 1990 circuit can also be used with fixed sound systems. What it does is trigger a set of LEDs...
This interesting circuit of the American publication Electronics Handbook Volume XIII 1993 shows a...
Found in American documentation, this circuit can make use of modern equivalent transistors. The...