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I'm trying to fix this amp which has basically two problems. It makes this horrible tea kettle like feedback and has very little clean headroom. I believe I have narrowed it to the power amp, as I plugged the line out into another power amp and had neither of these problems. All the voltages check out and so does the bias. I tried swapping tubes as well. Someone said it could be positive feedback, but I disconnected the feedback loop and no change. Your insight is greatly appreciated.
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also
Sorry I was writing quickly and forgot to mention that the distortion has somewhat of a phasing sound to it. Kind of a swirling. -
Since nobody else has replied i can offer this---- i have an AOR 50 and i've never gotten tones out of it that i really like----i 've done some de-gaining mods but it still isn't my (or anybody else's around here) cup of tea.
It sounds like you've done the basic troubleshooting to the power amp already.
i think that gutting the Laney AOR circuit and building a 2204 Marshall-type circuit on a turret board would be the best idea.
That's what i'm going to do to mine when i get time----no push-pull pots, no whacky switching, and tone response that i actually like.
If the problem with yours is in the Power Amp section, about the only thing you haven't checked is the OT---- swap another similar OT in for a test.....................gldtp99Amp Clips: http://soundcloud.com/gldtp99Comment
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The feedback you disconnected is actually negative feedback. Could be the cap in the negative feedback loop is bad (open) and the output stage is feeding back. Without a 'scope, I don't see how you're going to see what's going on. Your only hope is the shotgun approach, replacing parts one by one. If your voltages on all output tubes are OK, I would suspect a problem with the phase splitter.Comment
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