This circuit is from a March 1967 Radio Electronics. The circuit applies to general purpose SCRs such as the TIC106, C106 and others. The test is done by increasing the gate voltage to the trigger point.
This 4-transistor signal tracer or follower was found in Radio Electronics magazine from May 1960....
This 1967 Raytheon circuit uses an optical coupler of the era and has a range of 800 to 200 Hz....
Assembled with SMD components this circuit can be very small. The range is a few tens of meters. We...