I've had the best success, by a wide margin, using Sylvania 5751 blackplates in my Alpha. Female vocals are amazing with these tubes, as are vibes, piano and strings. On the other end of the scale, Mullard CV4004s and Telefunken 12ax7s didn't do much for my ears--distinctly grainy sounding. For current production tubes, I haven't tried the Ei 12ax7s that Newbee recommends, but have popped in a pair of cryo'd Electro-Harmonix, which were pretty good.
