Hi all,
Just wanted to say I am still really enjoying my VB-2. After playing through it for a few months, I came to the conclusion that while it was sounding great, it was sounding like a good solid state amp - missing the tube warmth that I was looking for. Also, the overdrive channel was very ugly even with the gain backed way off. So, in the spirit of tinkering, I wanted to play with tube selection... let the rolling commence. I picked up this amp used, with these tubes installed:
>2x JJ 12AX7's
>1x Ruby 12AT7
>6x Ruby EL34BHT
After some poking around on the web, I found a few threads on Talk(nice)Bass [hat-tip to Andy Irvine for that description], where the amp designer, Bobby, stated that the Ruby power tubes listed above were ideal for this amp. Given that I didn't have the kind of cash needed for power-tube experimentation, I took him at his word and left them well alone. The others were fair game, however.
Now is a good time to mention that it's helpful to have someone with skinny wrists for this job, as it's a bit tricky to get around the transformer and the power tubes to get to the 12AX7s - it can be done however, without having to dismantle the chassis. First step was to try alternate 12AX7's. I tried both Mullard and Tung-Sol reissues in both spots. The original JJ's were quiet, with very little break-up even when pushed hard. Swapping for the Tung-Sol's and the Mullards did give the capability to add some break-up when the gain was pegged, but they both sounded "flat" and lifeless. So back in went the JJ's.After a bit more homework, I read that the humble 12AT7 can have a profound effect on the amp overall. I plonked in a JJ 12AT7 and voila, the overdrive channel became useable.  ....
The excitement was short-lived, however, as although if did indicate that the Ruby 12AT7 was as much use as a chocolate tea-cup, the JJ was not the answer, as it severely muted the highs on the regular channel.... so off again to the interwebs. I was lucky to find a guy locally who repairs organs....I know this seems like an odd statement, but bear with me. Now the old organs always used good quality low-noise tubes, so it's a good place to go NOS tube-hunting, without having to deal with Ebay. I also learned that you can get 12AT7's for much less than 12AX7s.
Anyway, long story short, I added an RCA 12AT7 from my organ guy, and two Sylvania 12AX7's from vacuumtubes.net (because I couldn't afford the RCA 12AX7s I really wanted, and they got a good write-up). The RCA 12AT7 has made the overdrive channel useable as a second channel - if you back off the gain it sounds exactly like the main channel, and if you tweak the gain, you can get just the right amount of hair (the main channel stays clean all the way up - I decided I liked it that way in the end).
I had a lot of good email exchanges and discussions with Brent Jesse ( http://audiotubes.com/) and the folks at vacuumtubes.net (http://www.vacuumtubes.net/), and I learnt something along the way
YMMV of course, but I found the NOS tubes to be much more to my taste than the current crop of reissues. Sure you can get very bogged-down in chasing the holy-grail, but I managed to get some halfway decent 12AX7's for a good price, and score a great deal on 12AT7's from an unlikely source (also note that Ham radio gatherings also bring out the tube folks, or so I've heard).
Cheers 
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Thanks mate!