Need Help - Tube Amp Problems

Xcaliber

Xcaliber

New member
About a year ago I bought a tube amp from a local music store. This is the first tube amp I've ever owned as I've always had solid state practice amps. The other day I put the amp on an amp stand (I play at very low volumes and it helps if I angle the amp towards me). I noticed that the amps volume was much lower than usual and the sound was somewhat "muffled". I took it off the stand and turned it back on, but then I bumped the amp and I noticed that the volume came back and it sounded normal. I tapped on the top of the amp and it cut out again. Tapping it again a few times made the sound come back. I've done some Google searches and some posts pointed to a bad tube, but others said it could be a loose or faulty wire as well. I don't want to take it in for "service" if I don't have to and I don't want to buy new tubes if I don't have to.

I should also point out that the amp was sold as new, but I think it's either gently used or was "borrowed" from the store. I didn't noticed or suspect that until recently, but it could explain why a 1 year old amp needs a tube replacement already.

Any help/insight you can give me into figuring out what's wrong before spending money would be greatly appreciated.
 
Tubes don't have to be old to fail, or start to fail. They just do sometimes. You can get a bad tube right out the box. It could be a bad wire, bad solder, or something to that effect, but tubes are most often the problem. Cruddy tube sockets can be a problem too. Get back there and tap each tube individually with a pencil or something to see if you can isolate which tube it is. Also remove each tube one at a time, hit the pins with some contact cleaner, and work the tube in and out of the sockets a few times to clean them.

If you determine it's a bad preamp tube, no problem, just replace it with a similarly rated tube. Preamp tubes are cheap. If it's a power tube, it's usually best to replace them in pairs or a set. Then bias accordingly. This may be beyond your capability. Take it in for new power tubes if you've never gone inside an amp before. It's not typical for people to die from tube amp shock, but a tube amp does store enough voltage in it's innards to zap the fucking shit out of you.
 
Check each of the above... ^^^...like Greg said, but start by just reseating each of the tubes a few times to clean off any oxide.
That's the easiest to do, and costs you nothing. Carefull with the smaller 12Axx type tubes....easy to bend a pin if not ligned up right with the socket.

I just went through something similar on one of my amps. It was playing fine for awhile, then the volume would drop down to nothing, than back up, etc...etc.

I would have thought it was one of the preamp tubes.....nope....then swapped the power tubes....nope....then the rectifier tube..nope....
...ended up being the phase inverter tube. :facepalm: :D
Replaced it, problem gone.
 
Thanks guys. I've heard about the "tap the tubes" thing before, I'll give that a try. I think it might be worth it to just take it to my local store and have them look at it if that doesn't prove anything conclusive.
 
Try tapping or wiggling the volume knob. Could be a bad or dirty pot, or a loose connection (bad solder) to the pot.
 
Intermittent problems can be tough to locate. Especially for the untrained. Never forget that there are voltages in there that can ruin more than your day.
What kind of amp are you talking about here?
 
" to zap the fucking shit out of you." THANK! You Greg for causing me to spray coffee all over my qwerty!

With your permission I shall store that phrase away for use when The Muse otherwise deserts me.

And I am knocking too for a make and model number, Peeps, PLEASE always give M&M # otherwise help is MOST difficult. (if you can also do a bit of work and get a manual/schematic? Triffic!)

Dave.
 
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