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Thanks for the input bandit. I purchased my amp new in 2010 and it was made in May of 2010. To answer your question pertaining to the at7 tube manufacture one was a new Jan/Phillips, one was a new JJ, and the third was a used Grove Tubes. As to the condition after they started to have the ~60hz...

Thanks and let us know how it goes for you. To answer your question, my preference is running at7s in v4 and v6 at the same time. In my case the hum will start in a new at7 in v4 after a couple of hours (in channel 3 only). After that if I continue to leave that at7 in v4 the onset of the hum...

Perhaps my old tube books are dated but they indicate 330v for ax7 and 300v for at7. It is probably a mute point anyway since it is unlikely Mesa is pushing v4 to the limits.

Has anyone opened up their amp and run voltages on V4? While the max current on a 12at7 is greater than a 12ax7 the plate voltage max is about 10% less if I recall. The reason I ask is that on my amp after running the at7 in v4 for several hours channel 3 develops a faint noise similar to an ac...

Excellent call on the AT7 swap guys, I personally like them in both V4 and V6 at the same time. I purchased my amp new in early 2010 and this is the first time I have really bonded with it.