TS-382F/U audio oscillator

[maxhifi]

Picked it up at a hamfest back in the early 1990s for $5, the seller said he had another in his car I could have for free, but I rejected it on the basis of not needing two - now I wish I had taken it! Truly the definition of a boatanchor. It's an audio oscillator which more or less is a clone of the HP 200 series machines, with some additional features and much more rugged construction.

Anyway it's given me reliable service for years, however recently has developed a problem. It works great for about 20 minutes, and then the amplitude of the output starts jumping all over the place.

Previously, it would develop a small notch in the waveform after being on a long time, which the military service manual (thank you BAMA!) says nothing about, but the HP 200A manual says is a problem with the lamp in the oscillator bridge.. I substituted tubes for the oscillator and phase inverter, to no effect. I think all signs point to either a bad 3W lamp, or a dirty lamp socket. Capacitors are all paper in oil, and I suspect they are not the problem. Luckily my EICO 378 uses the same 3S6 lamp, so I can try the one from there.

Will be nice to get this beast going again.. it's always been a useful piece of test gear and its a pleasure to work with such well crafted equipment, makes me want to hunt down more military gear.