by soundmasterg » Mon Jul 25, 2011 6:36 am
It probably has something to do with the fact that the first section in that spot is a cathode follower. I would have to do the curves on that tube and see where it specs out, but I would guess that it is biased such that it introduces a compression effect. The 12AV7 can pass a lot of current and generally likes values similar to a 12AU7 around it in a circuit. When used with resistor values higher than that, it shifts its operating point. If it works and you like the sound, then its fine. If you adjusted things to be more optimal for that tube, then it would draw a lot more current and lower your preamp voltages down a bit overall.
Greg