12ax7 tubes on a Mesa v-Twin

[blaine1984]

Hi everyone, Google got me here in my search for an answer to a pretty silly question.

I bought a Mesa v-Twin about a month ago, used.
Being an electronic engineering student I was eager to open it to see what was inside it... made myself some ideas, wrote a schematic, it's pretty simple electronic from the inside... anyway, i didn't really like the Solo channel.
Dark sound, no gain... i tried to mod the feedback loop of the TL072 before the tubes, but it was pointless.

I almost gave up since today:
I remebered something important about the guy who sold me the pedal... he told me that he switched tubes.
I had him give me the old ones... so I switched the tubes and the gain was almost doubled! The sound now is bright and cutting.

So i was wondering... those tubes have no serial number except for the 12ax-7.
They look different:



The tube on the left is the bright one (assuming the guy told me the truth it should be the one from the original amplifier), the tube on the left is the low gain dark one.

Now, i'd never think that there could be so MUCH tone difference just switching 2 similar tubes, and I'm wondering... could my tone become even better?

Where can I find some reference on these tubes? How can i reconize them if there is nothing written on them?

Thanks!

[chipaudette]

I've got a Mesa Boogie Tri-Axis from the early-mid 90s and its got tubes that look like the exactly like our one on the left. Plugging my Tri-Axis into anything but a Mesa power amp, it sounds quite bright.

Your darker sounding tube seems to be newer (the logo is of their newer style as well). Maybe I'd like your newer tube in my preamp! Of course, the lower gain doesn't sound like a good thing for me.

Chip

[stokes]

"Now, i'd never think that there could be so MUCH tone difference just switching 2 similar tubes, and I'm wondering... could my tone become even better?"
Those are most likely Russian or Chinese current production AX7's.Try some NOS and you will see a big difference in tone.In my experience,any brand of good quality NOS is going to sound better than either of those two in the picture,I have some old used tubes that will sound better.Of course its all subjective,and NOS tubes can get expensive compared to those,but I find they are worth it.