Tubes in a Quad

[JMMP]

Hey guys, I bought a quad preamp in the last few months, and I have been noticing a thunk when I play on Lead 1 and palm muting. I presume it to be a tube problem, so I have it opened up right now and am not really sure what I am looking at as far as the current tubes go. I read these originally came with NOS Telefunken tubes, but the tubes in it say "MESA STR-12AX7-A (ECC83)" and one is pictured in the first picture below. I also bought a 20/20 that came with some extra JJ power and pre amp tubes. I swapped out those tubes and for comparison the second picture is a mesa chinese 1.

Unknown tube

Chinese tube for comparison

 

[masher]

I think you've posted the same pic twice, but I still don't understand your question.I would imagine after all these years the tubes have been changed, so it's a crap shoot as to what you got in there.
In the Studio preamp the schematic shows the lead channel is controlled by v1 + v3.I've been trying to resolve some noise issues by swapping tubes around and found 1 mesa tube just like yours that I had removed from another preamp made a loud bass like hum in v1 so out it went.
Look at the schematic, find which tubes control that lead channel, and try with a known good tubes, and see if it resolves your issue.

 

[JMMP]

I think you've posted the same pic twice, but I still don't understand your question.I would imagine after all these years the tubes have been changed, so it's a crap shoot as to what you got in there.
In the Studio preamp the schematic shows the lead channel is controlled by v1 + v3.I've been trying to resolve some noise issues by swapping tubes around and found 1 mesa tube just like yours that I had removed from another preamp made a loud bass like hum in v1 so out it went.
Look at the schematic, find which tubes control that lead channel, and try with a known good tubes, and see if it resolves your issue.

You're right. I just corrected it. My original post is kind of two questions in one. How to fix it, and the identity of the unknown tube.

 

[jonamojo]

Throw some jan phillips 12ax7's in there and watch your quad come out of it's coma.