#1
So I retubed my amp last week and it has all been fine. We were having a bedroom jam just now, and after 40 minutes or so of playing the volume on my amp dropped for a few seconds and dissapeared all together. I turned the amp off, left it for 20 minutes and then used it again and it did the same thing.

To summise:
-Played for 40 minutes fine, no problems
-Volume drops over a few seconds, then completly gone.
-Tried changing amp channels, clean to dirty and there was still no sound
-Looked through grill in back, all 3 pre amp tubes are glowing and both power tubes
-Put in standy for a minute or so, took off standby, still no volume
-Turned off, went and watched the England game for a bit, came back
-Turned on amp in standby, let warm up for a minute
-Took off standby, worked fine for 20 minutes of so then same thing happened
-Gave up, played acoustic

I'm using x 2 JJ ECC83s, 1 x JJ ECC83s gold pin, 2 x JJ E34L

I suspect I have a bad tube as this has just started after the change, but I'm not sure how to check this. Any suggestions or ideas? Should I put in the old tubes one by one till I find the culpret?
Last edited by ragingben at Sep 6, 2011,
#13
Sounds like dying power tubes to me.
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I've had tube amps for a while now, but never actually had any go down on me
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#14
That was my first thought, as there was none of the symptons I have experienced when a preamp tube has gone on me before. If it means anything, both power tubes looked to be ok. Just a thought - I had (very dumbly) my pedal board with 8 or s 9vo pedals drawing from a Gator GBus 8, a low wattage solid state guitar amp and a low wattage solid state bass amp all on the same socket. Could this have affected it? It would usually be just the amp and pedalboard?
Last edited by ragingben at Sep 7, 2011,
#15
try just straight wall plug > amp > guitar

then check speaker cables, batteries in guitar if applicable

I've heard of this issue before, I think it was narrowed down to tubes. Not sure which ones though.

edit - does turning it up bring the volume back, albeit quietly?

edit 2- try swapping tubes (edit 3- as in switching positions), cleaning contacts, and try the old power tubes if they're working and you know how to bias and all that.
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Last edited by 8footsativaist at Sep 7, 2011,
#16
I will when I get back from work. The guitar pickups aren't active. It was hard to tell as the rest of the band carried on without me and by that point I powered down, but I think the sound was there, just very quietly even, and this did increase when I cranked it briefly, but not by much. My amp is auto biasing, so it should just be astraight swap as far as I'm aware. The old power tubes were on their way out, but I will switch the position of the 2 power tubes that are in there now to ensure they are seated well. How would you go about cleaning the contacts?
#17
If you are having sudden volume drops, that would usually be the power tubes that are at fault. However, I myself have had one occasion where too much stuff got plugged into one electrical outlet by accident, and my valve amp power kept dipping until I plugged it into a different socket. I did have 7 pedals, three amps, a PA power amp, a mixing desk and a laptop running off one socket though, so it's not surprising it freaked out lol.
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Last edited by jukejointjohnny at Sep 7, 2011,
#18
If you want to know where the problem is then run the FX send to your mixer or something where you can monitor the signal. If the signal from the FX send dies when the amp volume dies, then it isn't the power tubes.
#19
Thanks for the replies guys, very helpful (unlike the top half of this thread ) I'm now running on a seperate outlet and I got the same problem, bang on like clockwork last night. Plugged my tuner into the FX send, and that picked up the signal fine (I was at home so didn't have a board). Pulled out the new tubes, and replaced them with my 2 year old EL34's, ran the amp for 2 more hours without a problem. So figured it is pretty much the tubes. They are all packed up ready to go back to hot rox for testing, hopefully this is problem solved! Thanks for your help!