Well, I finally had time over the weekend to run through my batch of preamp tubes in my Walkabout and decide which one worked best. The tubes at my disposal were as follows:
Mullard 12AT7/CV4024
JAN Phillips 12AX7
JAN GE 5751
Shuguang 12AX7C9
Telefunken ECC83 (smooth plate)
JJ ECC83S
The original Mesa tubes said "Russian 2" on them, but I don't know who made them.
Virtually all of the tubes mentioned above offered some kind of improvement over the stock tubes. However, most differences were very subtle.
The Mullard was by far the warmest sounding, and had a good deal of low mids - too much for the already mid-heavy Walkabout. Still, if you are looking to add some meat, the Mullard would certainly do that.
The JAN Phillips is a great all around tube. Very nicely balanced tonally, with good articulation.
The JAN GE 5751 also had good tonal balance and was a pleasant sounding tube - not harsh at all. However, with the reduced gain, it didn't overdrive as well as the others, which is something I like to do with the Walkabout.
The Shuguang was a bit of a surprise. Upon first firing it up, I thought that it might be the ticket. Very robust signal and tone, overdrives great. However, then I noticed that it was really bringing out the finger/string noise in a huge and somewhat obnoxious way. I don't know if this means that it was slightly microphonic, but it was not desirable. Too bad, because otherwise this tube has a lot of promise.
The Telefunken was the most articulate tube of the bunch, with a bit more upper mids than most. Very clean sounding tube with the Gain down and the Master up, and probably sounded the best of the bunch when overdriven. Good balance, too.
The JJ was very similar to the Tele. Not quite as articulate, but perhaps had sweeter high end. Overdrove quite well, though not as nice as the Tele.
By comparison, the stock Mesa tubes did not have as much articulation as any of the tubes above (though they were close to the Mullard in that regard), and the tone was not as coherent. They did overdrive quite nicely, though not as convincingly as the Tele or JJ. Granted, there wasn't a huge difference overall, but I would say that you can do better than the stock tubes, and it shouldn't cost you an arm and a leg.
Ultimately, it came down the JAN Phillips, the Tele, and the JJ. These three were the most similar sounding of the bunch. I ended up choosing the Tele for its articulation and best overdrive tone. The JJ would probably be my second choice, although the JAN Phillips was very, very comparable.
The Walkabout has a second tube which drives the MOSFETs, and after playing around a bit, I chose the JAN Phillips for that duty. It really is too bad that the Shuguang had that string noise thing going on, because it really kicked in the pre-MOSFET socket - most balls and gain of the bunch.
There are a lot of good tubes that I didn't get a chance to try, but there you have the results of my own very unscientific preamp tube shootout.
Hope this helps, Tom.
P.S.
I got my tubes from Doug's Tubes, and he was very helpful.
(or 5 if you count "Flat" @ 3).
