After replacing the FedEx-crunched 6L6 sextet in my Mesa (with matched Svetlanas dirt cheap at thetubestore.com), it was time to look at preamp tubes. Lots of folks balk at replacing tubes except when they're deader than dead, but look at it this way--the cost is about the same as a set of strings, and how many people do you know that stubbornly play the set that came on the bass until they're dead as a doornail? (One of my peeves is that magazines will test amps and preamps without using quality reference tubes--which frequently sound a lot more different than different amps and preamps). Anyway, first impulse was to try what had been the perfect tube for my SWR GP preamp, a 50s 3-mica Sylvania 5751. But despite their numerous virtues, 5751s put out 70% of the gain of 12AX7 types, and on this Mesa, my signal is going through three preamp triode stages (70% of 70% of 70% leaves only 35%). So I went to my favorite 12AX7 type, an 80s-vintage Tungsram ECC83. Back when I went through a marathon preamp tube taste test, this tube sounded markedly better than the fetish-grade $100+ Telefunken flat plate. So I got Tungsrams again from Steve at angela.com (I can't believe he still has any left at only $24 a pop). Quiet. Hugely spacious. Tremendously alive. Shimmering highs and thundering lows. Not that the Mesa and EH tubes that were in the amp were total dogs, but the change was like night and day. YMMV. Drummer may rush. Void where prohibited by taste.