I bought this little tracer on e-bay for a few bucks. The seller told me that it was in working order and in good shape. Well, just goes to show that e-bay is sometimes a "crap shoot".
This thing needed every capacitor replaced, along with some wiring. It also needed a thorough cleaning. The input stage was dead until I realized that the transformer was hooked up wrong. 50 years ago this was a "kit", and someone assembled it incorrectly. It must have been sitting in a worthless state like this since it was assembled.
It's used to inject a signal into a circuit which then can be traced along the main and various branch circuits until at some point it can't be measured or heard anymore (it has a speaker for audible signal response). At that point the problem component can be readily isolated.
Quite handy for fixing older equipment -- but it also produces some VERY high voltages and it can be dangerous.
It works, but almost every capacitor in this thing was the "sh#ts".