I have wanted one of these preamps for quite a few years now, and a couple of weeks ago I finally aquired one....YAY! I have spent the last two weeks playing around with it at home, with several different cabs, and I am really impressed. I really like just about everything this has to offer, especially the EQ. Yesterday I decided to open it up just to see what kind of 12ax7 was in there and found a Chelmer Valve branded tube, which I would assume to be the original. My Question, has anyone experimented with different 12ax7's in the RPM? How often do these need to get changed? The reason I ask is that I don't really like the drive past 11 oclock, it seems to get a little too compressed and a little 'mushy'. I am not actually planning in using the RPM-1 for heavy gain....so it doesn't really matter, but I am curious. Anyone out there on TB with some insight for me?