I'm looking to get less breakup in the preamp stage of my Ampeg V4, and have been thinking about swapping the 12ax7's for 12au7's (I have a bunch of originals from the 50's). I know that it isn't much of a big deal for many manufacturers, but for some reason I'm finding a lack of info on this for old Ampegs either here or in google world. Is there anything I should be wary of/made aware of if I attempt the swap? Has anyone done it, and if so, what were the results? Cheers!