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Old 03-25-2013, 10:15 PM   #1
getwylde
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Recto Uhh Ohh

Ive got one of the older triple rectifiers that I just starting having trouble with.
The other night when we had it cranked for a few hours the overdrive/distortion just kinda fell out. Like you rolled the gain knob way down. I talked to a friend and he thought it was tubes. They were pretty old so I just went ahead and put 5 new 12ax7s, 3 rectifier tubes, and 6 new ruby el34 power amp tubes. No change.
Further tinkering and found that it only does it with the orange and red channels. You can turn the gain knobs up from 0 to halfway, no issues, but turning it any more than that it starts fading away and the amp makes noise like am radio static. It doesn't do it on the clean channel, just both dirties. Anyone had this problem before?
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Old 03-25-2013, 10:20 PM   #2
Robbgnarly
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How old is it?
It might actually need to be recapped, but it is impossible to tell. Take it to a tech
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Old 03-25-2013, 10:32 PM   #3
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Yea, could be caps, but it also sounds like it could be a problem with the optoisolators being used for switching, or any number of other things. Take it to a tech.
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Old 03-25-2013, 10:46 PM   #4
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I say mess with your preamp tubes some more and hit the pins with some contact cleaner. Then send it to a tech.

I mean - did you buy 14 new tubes just now?
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Old 03-26-2013, 04:50 AM   #5
MESAexplorer
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Caps usually degrade slowly over time, rarely will they just up and die like that. And usually that's well over 20 years for that to happen.

I had an issue similar to this with my F-100 way back in the day. What ended up happening is when the tubes went, it actually burned part of the board and blew a fuse. Obviously you're not having a fuse issue because it will actually turn on, but I'd probably open it up and give it a look.

I would assume something in the gain stage crapped out or possibly a transformer problem.

Obviously you hear something weird, does it feel really hot (hotter than normal) in any particular places, do you smell anything burning, or see any of the tubes lighting up brighter or dimmer than the rest?
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Old 03-26-2013, 07:43 PM   #6
some_dude_2
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What brand of preamp tubes did you install?
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Old 03-26-2013, 08:02 PM   #7
R45VT
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Quote:
Originally Posted by MESAexplorer
Caps usually degrade slowly over time, rarely will they just up and die like that. And usually that's well over 20 years for that to happen.

I had an issue similar to this with my F-100 way back in the day. What ended up happening is when the tubes went, it actually burned part of the board and blew a fuse. Obviously you're not having a fuse issue because it will actually turn on, but I'd probably open it up and give it a look.

I would assume something in the gain stage crapped out or possibly a transformer problem.

Obviously you hear something weird, does it feel really hot (hotter than normal) in any particular places, do you smell anything burning, or see any of the tubes lighting up brighter or dimmer than the rest?



Caps can die in many ways... There a few different styles in there. Doesn't really sound like a filter cap, more likely a coupling cap for the gain stages, however you typically get popping and other things rather than just lack of gain.

What mmolteratx said as well.

If messing with the preamp tubes don't work then take it in.
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