My B-52 ATX 100 is my main amp I use with my band and leave at the shed we practice at. The other day I went and just chilled and jammed with my bass player all night. This has been the first time in about a week since I'd been over there. I noticed all my settings on my pedals and amp were weird, but figured someone had just been experimenting, which doesn't bother me since I used a sharpie to mark my favorite settings a long time ago.

We'd been working on music at low volumes, chilling and drinking for about 4 hours, so of course the amp was running pretty hot. After picking the guitar back up after not playing for a few minutes I noticed the amp was suddenly very quiet. I checked my signal path and everything, and finally plugged directly into the amp. The signal was very weak, and when I strummed the guitar harder it had a weird buzzy "blat" sounding distortion, though I was on clean. I slowly turned the amp up to about 7, which should be louder than the volume I use to keep up with my heavy handed drummer, but it sounded like it was on about 4 and had that nasty distorted "blat" noise.

Of course at this point my friend's like "Oh yea, this happened the other day, but then it got better blah blah blah" which kinda pissed me off that he didn't tell me about the problem when he saw me putting all my settings back that he'd obviously messed with when the amp started acting weird on him. Whatever, that's not the point.

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I've also had occasional weird noise in the past while playing. Like if I hit the low E and let it ring out at a high volume every once in a while I'd get this weird ringy sound, almost like a little jingle bell in my amp. The first time this happened I disconnected the reverb tank since it sounded like it might be a spring vibrating. When this didn't fix it I took it in for repairs. The guy couldn't find anything wrong with it - I'm guessing he never heard the sound since it's so intermittent - so I stopped worrying about it.

Does this sound like a bad tube or something worse? If it's just a tube(s) then I'm sure I could replace it/them myself, but I want to know if that'll accomplish anything before doing it. I also wouldn't really know what to look for, but I'll worry about that once I know whether or not that's what I need.
Last edited by The4thHorsemen at Mar 13, 2014,
Microphonic preamp tube, almost certainly. You can test by tapping the tubes with a pencil with the amp on. You'll hear a good loud thump when you hit the bad one.
Sounds like tubes to me. Your main issue seems to be power tubes, but that weird noise you had before may be a bad preamp tube as well.

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Could the preamp tube be causing the main problem or is it more likely to be two different problems? Are preamp and power tubes both tested by tapping them? And what if the amp runs fine next time I turn it on? Will I have to run it for a few hours to get it hot again, or will the tubes make the thump noise regardless?

And I've heard you can replace preamp tubes one at a time, but if it's a power tube then all the power tubes need to be replaced, is this correct? I've probably had this amp for about 4 years and I got it used, so I'm kinda wondering if I should just change em all anyways.

Also, I'm sure I'll need help selecting what tubes to buy, but I guess I'll worry about that once I've checked and made sure.
When your amp is making the weird buzz distortion and cuts
out check out your power tubes ones probably flickering or
fading as the noise happens. You should replace all the power
tubes with a matched set. Pre tubes turn your amp on and do
the tap test like mentioned above. I'd find the dud pull all the
good ones for spares and get new pres to.
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I had a similar problem on my JCA. we all thought it was a preamp tube, but unfortunately there was a damaged output transformer. No bueno. But I got that fixed up. problem solved.
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You should have a spare preamp tube anyway, so buy one. Then try it in every position until the problem goes away.
If it's still no good - power tubes.

That's the cheapest strategy, because as I say, you should have a spare anyway.
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Might as well give it all new tubes.

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Hm, I think I'm going to do the pencil tapping test before I decide on anything, but I was just looking at all the brands, models, and price ranges for tubes and feel like I have no idea what to do.

Just looking at 12ax7s on Tube Depot, which was just the first site to pop up on google, the price range is from $9 to $250 for each tube. I obviously don't want to spend a whole lot, but at the same time I want a decent sound. Within the $10-$25 range there are like 15 different ones to choose from and I have no idea what I'm looking for. Help?
Just grab a JJ ECC83S
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Marshall 1960A
Boss GT-100

Cathbard Amplification
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^ yep that is a safe bet JJ are a decent tube and cheap.
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