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So I have a Peavey ultra 120 + and it was working great then outta nowhere it stopped making any amplified sound. No hum unless you turn it up to max volume. The two left preamp tubes no longer glow. I've replaced all power and preamp tubes and checked fuses, every single thing looks health inside. No burning /burnt smell either.
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The four small tubes have their heaters all wired in series between +24v and -24v. It is hard tp imagine why two of them would go dark. generally I woulod expect all four to light or all four to go dark. Turn out the room lights and look more closely to see if they might be running after all.
Plug the guitar into the FX return jack. Got sound?
My primary suspect in these cases is little transistor Q5, the muting JFET. If it gets stuck on, you lose your preamp out.Education is what you're left with after you have forgotten what you have learned. -
Enessyia - Yeah man I made sure to visually look it over in a dark room, the first two do not glow neither do they produce heat. And yeah I plugged in a cable to the fx loop and produced sound with my thumb.Originally posted by Enzo View PostComment
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Ah, wait, I was thinking Ultra, not Ultra Plus
Your preamp tubes are still series one pairs of 24v, but they do ground the center of all that, so your first two tube heaters are wired across +24 and ground with a pair of resistors in series. They are probably open. Find R301, R302, they are next to each other nestled into the space between pins 1 and 9 of V4. 22 ohms apiece in parallel - 11 ohms in series with the tube heaters. If they open, you lose those two tube heaters.
Of course it could be something else, like a broken connection to a socket, but my money sits on those resistors. Conceivably C301 is shorted or seriously leaky, and that burnt out the resistors. If the resistors are intact and that cap shorts, I;d expect low voltage fuses to blow and those resistors to be scorching.Education is what you're left with after you have forgotten what you have learned.Comment
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