I recently picked up a Marshall AVT20 for use as a secondary amp. It is my first experience with a hybrid amp and I have to say that I am more impressed with the amp than I expected to be and that it looks like it will suit my needs perfectly.
That being said, the overdrive channel has a bit too much gain for me. I was reading over on the other Marshall forum that someone had swapped out the stock tube for one with a lower gain factor - they had gone from a 12AX7 to a 12AT7. Apparently this gave a bit more headroom on the clean channel (headroom isn't an issue for me but I don't mind if that is increased a bit) and smoothed out the gain on the overdrive channel. Some others swapped theirs for a 5751.
I was wondering a couple of things before I go ahead and do that. First, has anyone here put a tube with a lower gain factor into their AVT or other Valvestate amp? If so, which one and how did you like the results? Second, since I know squat about tubes I was wondering if anyone could recommend whether I should go with a 5751 or a 12At7? Or might that simply be a personal preference thing? And finally, should I buy a JJ, a Groove Tube, EH, or whatever other brand?
Thanks in advance.