So lets see. I've had a 400+ for a while, and was pretty happy with it. I've searched many threads on tube replacements and such, and got a lot of good help from one of Psycho Bass Guy's threads. I was looking for a preamp change so I went with some Tungsol 12ax7s, and a NOS (american made) Tungsol 12au7. Put 'em all in- amp didn't work. Through process of elimination, I discovered a bad tungsol 12ax7 that was causing the problems. Good thing I ordered one extra, just in case. So lets see...12au7 as the driver tube of the preamp, the other three slots filled with the new production 12ax7s. When I first started up, there was an enormous volume difference- absolutely no volume at all (figuratively speaking). I let it warm up a bit more, and after a couple of minutes, everything was great. Normal volume, absolutely beautiful tone, very happy results. I assumed this would be the norm, that I'd just need plenty of time for the amp to warm up before it would be at normal operating conditions. I went to band practice the next day- not good. It was a very laid back practice since the drummer could only be there for less than an hour, so I ended up spending a lot of time just chilling and playing at pretty low volumes. The amp did the same lame no volume thing for hours and hours on end. If I tried to turn it up to a good volume, it would distort like crazy before being anywhere near the correct volume. This is at 4 ohms going into a 210 and 115 btw. There was a break for about an hour after about 3 hours of uselessness. I went out and fired up the amp again- in under 15 minutes, it was back to magical wellness (or atleast close enough if not perfect). Practiced again a few days later- same gay **** for a while, but became normal after probably half an hour. Now it becomes last friday (15th), and it's the afternoon before my first gig with this death metal band I joined. Gave the amp plenty of time before hand, but it still pulled similar crap- just being extremely finicky. So I ended up using a hartke 3500 that I hadn't sold yet, for the gig. Pretty lucky I haven't had a buyer for that amp, and just happened to still have it at this time. It actually sounded pretty decent for the show, though I would have LOVED to be able to use my mesa instead. So now I'm here whining about my finicky mesa, when you all are thinking that it's clearly just a problem because I put the 12au7 in the driver stage of the preamp. Well, yeah, I'm gonna swap that out and see if it fixes everything, but I'm still very unsure. Before any of this trouble, I loved the way this tube amp sat in our death metal mix, but I've never been completely absolutely blown away by the tone. In a softer rock setting, I was constantly battling with a lack of lows that I wanted, and that honky upper mid characteristic. Tone aside, this amp has always seemed a bit finicky for me. I'm wondering now if I'd be much happier with a nice reliable hybrid amp, or other solid state driven device. Maybe my inner gas is just urging me to try my possibilities with other all tube amps, because I'm really itching to try some type of svt. But maybe I would just be better with a racked ss amp, that I wouldn't ever have to worry about. What's everyone's opinion?