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Old 15th January 2011, 04:08 PM   #11
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Originally Posted by wrenchone View Post
Those coupling caps really need some sleeving on their leads. With all those leads snaking around, they're just aching to short against something.
I would NOT power up this amp until this was taken care of. You are just asking for a destructive failure.
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Old 15th January 2011, 05:34 PM   #12
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I would NOT power up this amp until this was taken care of. You are just asking for a destructive failure.
Guys I understand. The depth of field is flat in the picture so it seems more cramped than it is, no leads are touching
anything else. The oscillate = blue I will check out. I am not happy about the size either and will insulate leads, but they do not appear to be the issue.
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Old 15th January 2011, 06:30 PM   #13
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The wires on many of those capacitors really appear (regardless of depth of field) to be touching their cases where they bend around the ends. The cases are metal and therefore conductive. I'd recommend teflon sleeves on all of them with a careful re-installation.
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Old 15th January 2011, 06:42 PM   #14
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The wires on many of those capacitors really appear (regardless of depth of field) to be touching their cases where they bend around the ends. The cases are metal and therefore conductive. I'd recommend teflon sleeves on all of them with a careful re-installation.
I see what you're saying, I misunderstood what you guys were talking about. Yes I think some of the leads may have been touching the cans . I thought the references were to leads touching other leads... Sometimes I miss the obvious.
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Old 15th January 2011, 07:04 PM   #15
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I see what you're saying, I misunderstood what you guys were talking about. Yes I think some of the leads may have been touching the cans . I thought the references were to leads touching other leads... Sometimes I miss the obvious.
Happens to all of us, and I bet these leads are at the root of your issue. I suspect it will work just fine once you address this issue. Changing out the coupling caps is a simple upgrade I have found to be effective in a lot of budget and vintage amps.
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Old 15th January 2011, 09:34 PM   #16
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if these caps are interstage caps and one wire (+) touches the can you will have a link and not a cap, that link will pass the voltage that is present at the anode of the preamp tube, ie. not good!

Other than the problem with excessive voltage at the output tubes grid it can also cause oscillations due to heavily changed operating point.
(and even cause oscillations thrue the feedbackloop if present.)
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Old 15th January 2011, 09:39 PM   #17
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I put in some smaller caps and insulated the leads. Biasing is back to normal. So far so good. Thanks everyone.
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Old 15th January 2011, 10:15 PM   #18
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I put in some smaller caps and insulated the leads. Biasing is back to normal. So far so good. Thanks everyone.
great news!!

Actually, i was impressed by the building quality inside, it actually looks like a very high quality amp
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Old 15th January 2011, 10:49 PM   #19
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great news!!

Actually, i was impressed by the building quality inside, it actually looks like a very high quality amp
Yeah, not bad for $500 (used)!
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Old 16th January 2011, 06:11 PM   #20
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http://www.diyaudio.com/forums/attac...-schematic.jpg

6922 is a TP... What's the pentode section doing.. or is it incorrect tube number ?

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