Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: CascoSieg on December 15, 2021, 03:13:40 pm
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I've been wrestling this one for a while. The right channel of my stereo SE produces a staticy scratchy sound when volume is up in either channel. It definitely seems vibration/volume and not signal level related - so it happens using clean or OD channels, always starting at about the same volume. You can hear it in the 15 second snip linked here.
https://soundcloud.com/cascosieg-168399771/right-side-scratchy
Can't reproduce it with the chassis on the bench - just in the cabinet.
Once the amp is loud enough to induce the sound, the scratchy sound gets louder as I turn up the R master volume.
I have:
- re-secured output tube sockets to chassis
- changed output tubes v4/5
- changed driver tube v3
- re-soldered all v3, 4, 5 socket pin connections and retentioned pins
- re-soldered all above board connections between driver and output tubes.
I haven't tried swapping the wiring to the transformers to rule them out - do damaged OTs make that kind of sound?
If it could be a faulty component, and guesses as to which are most likely culprits?
The next thing will be just disassembling and rebuilding that part of the circuit from fx return jacks through the power section.
Thanks very much for any ideas!
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Some of the solder joints look dodgy.
Is the cab screened?
Combo, with a speaker in very close proximity?
It may be oscillation, what does the scope show?
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Heyo. Nice sounding amp! And a very nice build, too, by the look of it.
I have an SE stereo amp I built recently which had a similar problem. I found the problem by chop-sticking components with the amp fired up on the bench - it was a faulty (although brand new) resistor in the preamp section - forget which one right now, but it was in the tone stack on one channel of the amp. That has never happened to me before with a new component, but it was a nice surprise to find the problem so easily.
Hope that helps - good luck with the search.
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"Some of the solder joints look dodgy."
- Yes. I suspect you mean some of the turret joints look a bit cool? I should probably pull some of those apart and do again.
"Is the cab screened?"
- I've checked it with the wood/cloth speaker cover off, and there's no difference.
"Combo, with a speaker in very close proximity?"
- I also hear the problem if I run one channel to a 1x12 cab on the shelf right beneath the combo.
"It may be oscillation, what does the scope show?"
- Ah, haven't done that yet... will do tomorrow.
Shaun, I've done quite a bit of chop-sticking and just can't make the sound happen. But, it's good to know that a faulty component could cause such a problem.
Thanks y'all!
Thanks!