is this a tube problem?

[deftincu1]

I was practicing with my band today, and the weirdest thing happened. My amp was set at the perfect level with everyone else, and we had already played all but one song in our set, when we started to play the last song I noticed that my amps volume had jumped up dramatically! I had my output set at about 10 o clock originally, but after the sound jumped up I was able to turn the volume down to about 7 o clock, and had the same volume as i did before. I checked all of my levels on the loop, and my pedals, and there was nothing different. I also noticed that when I turned down my output level all the way to nothing, I could still hear a little bit of sound. Is this a tube problem? I have seen stuff all over this forum stating that the volume of the amp decreased and gets lifeless when a tube is going bad, but I haven't seen anything about the volume jumping up. Has anyone else experienced this? Can anyone tell me what could be wrong? Any help would be appreciated. Thanks.

 

[Metaghius]

i would check the preamp tubes one at a time...

 

[94Tremoverb]

I doubt it's a tube problem - when tubes go out they reduce the volume, not increase it. It's just possible that a tube had been making a bad contact with its socket for the whole time you were playing it before, then fixed itself (maybe due to heat, if the pins expanded and made a good connection) just before your last song. Or maybe the problem is a bad ground connection on the Output Level pot, which would cause both the volume to jump up and the control not to go quite to zero.