I love my little walkabout and have upgraded the tubes to a set of JJ ECC83S. It made a remarkable difference, but I'm finding that I don't really want or need the OD grind of this amp. I prefer the clean tone, but the volume isn't usually sufficient with the gain turned down as low as I like (9:00 or so). Is there a tube out there that will allow me to crank the gain a bit more and still remain comparatively clean? Maybe a 5751 or 12au7? Or will the design of the preamp make sure that OD happens regardless of the tube?