Tube amp trouble...
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Posted on Apr 01, 2005 03:59 pm
Johnny Hero
Member Since: Apr 26, 2002
It's an old mesa boogie dual rectifier.
It sounds amazing, but when I crank it it has this horible rumble that sounds like the damn thing is about to explode! If I give it a good wack (I know, I know, I shouldn't do that) it'll stop, but as soon as I start playing it starts up again.
If it's not making the noise and I tap on one of the tubes, it starts making the noise again. Tap a few more times and it'll stop. It does this on MOST (but not all) of the tubes.
So do I need new tubes or what?
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TadpuiI am not a crook's headMember
Since: Mar 14, 2003
Apr 01, 2005 04:10 pm Take it to a tech that you trust and have them take a look at it. Maybe one of the tubes is microphonic, or just plain dead. Just don't go poking around in there yourself...the capacitors in tube amps can store lethal voltages for quite a long time, even if the amp is unplugged.
How long have you had the amp, and how often do you play it? I think that power tubes should be replaced once per year if you play it loud regularly. Preamp tubes can last twice that as far as I know.
Apr 01, 2005 04:13 pm I bought the amp used about 4 months ago... I have no idea when the tubes were changed last.
I took the amp into my local shop about a month ago and they looked at it and said it was fine, no problems, no odd noises. But now it's making them again, so I dunno what's going on.
TadpuiI am not a crook's headMember
Since: Mar 14, 2003
Apr 01, 2005 04:19 pm Mine did the same kind of thing to me...it was making terrible crackling and popping noises, even when there was no instrument cable plugged into it. The shop kept it for a week and was never able to recreate the problem. Along came spring and warmer, more humid weather, and the problem went away. Winter came again and the noise started up again. I just attribute it to the extra static buildup due to the cold, dry air.
It's like having your car make a weird noise all the time, but when you show up at the mechanic, all is well until you drive away. I hate that!
BeerHunterwww.TheLondonProject.caMember
Since: Feb 07, 2005
Apr 01, 2005 04:26 pm Ahhh, the old proximity repair. We support about 100 computer users and many times when they report a problem, it goes away with our presence. We refer to this as a proximity repair.
On the serious side, please be carefull as Tadpui
has said. Serious lethal voltage inside.
Apr 01, 2005 06:43 pm I think I'm just going to tell them I want it re-tubed anyway. Hopefully that will fix the problem.
jmailjimmie neutronMember
Since: Feb 14, 2005
Apr 02, 2005 05:49 am You've probably got "cold" solder joints, or bad capacitors involved in there. Have you tried disconnecting your reverb tank (if it has one)? Does it do the "noise" after the amp is "warmed up", but not at all when it's cold? High volume and not low? My brother has fixed his Twin & his Marshall, both with the same symptoms, but he knows his stuff. It is very dangerous inside an amplifier. After all, it "amplifies". Extremely high voltage is involved, and it's "stored-up" in there, like an old TV does. A good tech will find the problem. Just replacing the tubes may help, but if it's not the tubes... that's kind of expensive. Of course, most good techs will cost even more...
pjkPrince CZAR-mingMember
Since: Apr 08, 2004
Apr 02, 2005 09:28 am My guess is a microphonic tube, that it's doing it in lots of spots is kinda strange, but not uncommon. The preamp tubes can be replaced with the same type, but the power tubes should (big should) be checked for bias when they're replaced. I can't remember if a recto is fixed bias, but I'm pretty sure it is. If you're inclined to tinker with it a little (I know I am) then you can purchase a few good NOS 12ax7 preamp tubes and start swapping them out and checking for sound. It's very possible that you'll fix the problem that way and it's not overly expensive for you, plus you get some experience working on your own amp.
You can also swap your power tubes yourself, but I'd recommend caution as others above have done. There's a few ways to bias, some very dangerous, some safe but a little more expensive. This can be left to a tech, as they'd be prepared and know how to do it right.
As far as the other possiblities jmail mentioned, they can be possible, but if the tubes are of unknown age and condition, then I'd start on those first, as they need to be replaced every so often anyway.
To add to what jmail mentioned, old resistors can start popping like mentioned, if it's a cold solder joint, then you'd probably have total cutout, and/or loud snaps as the voltage cuts in and out. Caps can go bad as well, though signal caps rarely do, and electrolytic caps usually start acting funny sounding, not staticy or popping.
Hope this helps.
Apr 02, 2005 11:22 am From what you guys are telling me, I'm pretty sure it needs new tubes. I think I'm gonna take it down to the shop today and have it re-tubed.
