So, I managed to score an SVT-4PRO at a decent price used, and I'm waiting for it to come in... ...So, I'm already preparing to want to change the tubes. Luckily, I've got a pretty good stash laying around. According to Ampeg, the preamp only has 3 12AX7 tubes. I thought it had a fourth 12AU7, but I guess that's only on the SVP preamp. As for their function, I'm not sure of V3, only V1 (input gain) and V2 (EQ). I'm guessing V3 is for the output or graphic EQ? In my stash, I have these: 2x Tung-Sol 12AX7 (Current production, matched set and balanced) 1x Tung-Sol 12AU7 (Current production) 2x Chinese 12AX7 (Marshall pull-outs, pretty sure they are Shuguang) 2x Sovtek 12AX7-LPS 1x Sovtek 12AX7WC 2x GE 5751's (matched) Bunches of GE 12AU7A's of varying age I'm just curious what some other guys have tried. I know a few people like GE's. Personally, I'm not a big of JJ's...they seem a little too dark for me. I've tried a few RCA's and not been too thrilled with them. Maybe they were just worn out, I don't know. I understand from reading on these forums that V1 will make the most tonal impact, so I was thinking of just using the matched Tung Sol's for V2 and V3 and use either a GE 5751 or the EHX 12AX7WC in that position.