My Mesa DC-2 was a lot quiter before I replaced the tubes, so I thought: well damn, maybe the new tubes are bad....or need a "burn in".....or something else....
So I put the old tubes back in and -- surprise -- hum is still there ! ! ! Amp was quiet with the same tubes just minutes earlier.
I was reeeel careful getting them in and out. Could I still have jostled something loose? Mesas are supposed to be tank-tough.
Mesas are also "fixed bias", which -- if I've got this right -- means that if you replace with Mesa tubes (which I did), they are already pre-tested by Mesa to match the bias of the amp. Also, the power tubes were bought as a matched pair. In theory that shouldn't matter, since all Mesa tubes are supposed to be matched for all Mesa amps. That's the theory anyways......
What gets me is that the hum wasn't there with the before-moved old tubes, but is there now using either the new tubes or the re-inserted old ones.
Someone suggested contact cleaner -- maybe some flakey stuff came loose in there from off the pins of the old tubes when first removed.
Outside-of-amp stuff (cables, etc.) was same condition pre-hum and post-hum. I usually do a pretty good job keeping these things clean.
Oh, and the sockets are cherry-tight.
