I'm currently listening to my 129 with an EI 12AX7-a dramatic improvement over the no-name tube that came with it. In fact, I was about to dump the 129 until I started rolling new tubes into it-so far, I have tried just the EI 12AX7 and the JJ/Tesla ECC83S, both of which sound very nice and are good enough to make me want to keep it and do some more tests. Both tubes I tried sound fantastic with guitar and vocals, which makes sense since they are also preferred for many guitar amplifiers. The 129 also has 8 pin DIP sockets for the opamp driver stages (there are 4 dual Rolm opamps-2 per channel), so I may try to "roll" some new opamps into that front end to see how that affects the sound-a lower noise front end can only improve the already great sound.