I've been doing some tests lately, comparing 6l6 to el34 in my dual rectifier
, I'm using a 1960BV cab.
When I got the amp (used) it came with JJ E34L installed in it and 2 electro harmonix rectifier tubes and 2 JJ 12AX7.
It also came with the original tubes so I can try them too.
I played with the E34L installed for a while then after recording the amp a little I decided to try the 6l6 and see if I'd get better results.
I didn't change the rectifier and 12ax7 tubes yet (still has the non original ones installed) but so far I think I prefer the sound of the 6l6 for recording.
The E34L doesn't have enough hig and low and the mid peak is cool but it has some frequency to it that make it sound harsh more easily.
With the 6L6 I can boost the mid on the amp eq and it seems to sound more even without the nasty peak...
So far so good, I'm curious to try a better set of 6L6, apparantly the mesa ones aren't the best, but they're still better for recording than the E34L IMO.
The E34L have a cool in your face tone to it which is nice for live though.
I'd be curious to try out different preamp tubes as well, any idea of what I should try for my mesa?