TS-382F/U audio oscillator - Videokarma.org TV - Video

maxhifi · #1 12-23-2015, 03:58 PM

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.

stromberg6 · #2 01-11-2016, 03:54 PM

Hi maxhifi, That's the exact problem I have with my TS-382. After warm up, a short time later the output develops a "blip" in the wave form. I've tried caps, but had to put it away for a while. I'll try to get back to it soon, after I clean up a few other repairs currently on the bench. If I discover something I'll post it, or send a PM. Good luck with yours!
Kevin

maxhifi · #3 01-11-2016, 04:39 PM

Hey - try change the 0.5uf coupling caps, the blip on mine was caused by a shifting operating point of the phase inverter tube following the oscillator. After warm up the bias would drift due to a leaky capacitor and the tube would go into asymmetrical clipping, causing this blip. The feedback of the circuit helped clean up the waveform at the output into just a blip but at the cathode of the phase inverter it was really ugly! If your caps were bad a while it could have caused excess plate current and damaged the plate or cathode resistors, so check all voltages in this section.

Of help to me find in the problem was to allow it to fully warm up for an hour with the heaters on, until it began misbehaving, and then look at all the waveforms with my oscilloscope. Also, set the regulated voltage, and check the plate voltage on the 6V6. Mine had toasted the three parallel 10k plate load resistors, causing two to open and one to drop in value to 600 ohms, understandably ruining the THD spec of the oscillator. I also changed the 3W lamp as mine was stuck in the socket and I wrecked it. Now the oscillator works flawlessly and THD is less than 0.2% according to my heathkit IM-58 and that may well be the heathkit's residual distortion.

Now what I really want is an R-100/URR !

stromberg6 · #4 01-12-2016, 09:13 AM

Thanks! I will try what you suggest.
Kevin

maxhifi · #5 01-12-2016, 12:02 PM

On mine I changed only two capacitors - the 0.5uF "bath tub" coupling capacitors. The remaining bath tub capacitor is for filtering G2 of the oscillator tube so leakage would g be such a problem. Probably it would be prudent to change it too but I had only two on hand and wanted just to make it work. All the capacitors on top of the chassis appeared fine on mine.