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Discussion in 'Amplifiers' started by NBW, Oct 15, 2021.
It’s occasional and annoying. The amp in question is a Gibson RV Super.
Tubes? Guessing not many on here are fluent on Gibson amps past general knowledge.
Squealing and popping is usually a microphonic preamp tube. Not always, but often.
If you tap on the tubes with a chopstick or pencil, with everything unplugged from the amp, and you hear tapping loud and clear from the speaker when you tap one of the tubes, it's that tube. All you have to do is replace it.
Note, however, that sometimes you hear some tapping when you tap on the v1 preamp tube (the one closest to the input). That's normal, unless it's quite loud.
This is exactly the kind of advice I need. I think I put in a matched set of power tubes not that long ago and I was hoping that wouldn’t be the issue.
I hope to heck I'm right! But you'll know once you do the tube tapping thing.
I agree with Les, tubes would be the first place I’d check. There is an article Mesa/Boogie put out years ago detailing it, and is a good basic rundown:
If the problem isn’t found there, most other items are internal and require a bit of electrical knowledge to “keep from releasing the magic smoke” from the circuit.
I just had a similar issue from a set of power tubes I picked up. Rattle and popping, no squealing. Swapped back to old tubes and problem went away. Haven't diagnosed any further yet.
It might be in the power section, you never know, but it’s the squealing in particular the hints at a preamp tube. It’ll make that noise, often, with a guitar even plugged in. I’m curious to see!
I agree. Initially it freaked me out a little bit, more so the girlfriend with the pop. Part of my troubleshooting 101, I trace back to the last thing done and go from there. I do think I have a preamp tube issue as well. In my case I'm wondering if the new tubes amplified the issue.
Thanks for the useful link!
Les is correct about checking for microphonic preamp tubes with a wood pencil, chopstick, or wooden spoon, etc. However I've also recently had some power tubes going bad, which resulted in some crazy squealing & intermittent cutting-out. I peeked around back to see one of the two power tubes glowing purple-red in a way that didn't look good. Turned it off right away, then changed the power tubes... all better now.
I can vouch for getting whacked with a wooden spoon. They were my mothers weapon of choice.
I’m a survivor.
You, too, must have gone microphonic!!!
Yup. Hence the spoon. Problem fixed.
Yup. Tube amps are pretty simple beasts. First thing to do is check the tubes.
After tapping on stuff I think it’s the phase splitter. This amp has a ton of 12ax7s - 5 of them and two 12at7s. I just ordered a bunch of JJs as they are inexpensive and apparently came stock. It is an amazing and somewhat idiosyncratic amp.
Well I was wrong. I replaced all the pre amp, effects loop and reverb tubes. It was still popping. Then I looked into the power section (the front panel was off) and I could see one of the el84s glow super brigh and the it would pop as it discharged.
that was one of a matched set of JJ el84s I installed not too long ago. I put the Mullards that came in the amp back, which cured the pop, but now it’s noisy (probably why I retubed it.
New Mullards are just re-branded Sovteks. With an EL84 amp tube matching is less important. I'd just put the working JJs back in, and buy another JJ. For new tubes (as opposed to NOS), they're usually pretty good.
I think the Mullards have lower output and somehow worse shielding. I just ordered another JJ el-84 so I’ll put those back shortly.
I'm an NOS person, so, yes, kinda spoiled on very good, classic tubes. However, IMHO of the current tube offerings, JJ are perhaps the least problematic.
Seems like it’s fixed now. Sounds fantastic again.