Just landed a EICO 147 Signal Tracer. This is the one piece of test gear I didn't have. This one uses a 1629 magic eye tube for it indicator. It is going to be fun hitting up an National NC-300 receiver I have. It does not come with it's probe I have a couple here that may work however the schematic for it's probe, and for other signal tracers are to be found at the site below. it is just a crystal diode and a resistor, I'll take one of the probes I have and rebuild it to suit.
http://www.ohio.edu/people/postr/bapix/SigTrac2.htm

Very nice

I used to have several of those. A neat feature is that you can plug a set into the front AC outlet and use the "magic eye tube" to get an approximate wattage for whatever is plugged in the front. You can also use it as a test speaker (straight up or through an audio output transformer).

Where those really shine is their primary purpose, as a signal tracer. They come in pretty handy, especially troubleshooting audio amps.

I used an old solder sucker housing to make a probe for my tracer... looked good and works good.
Carl