I have a Mesa 400+ that I liked a lot for electric bass. It has new Ruby power tubes in it, dunno what preamp tubes are in it. I can check and report back...I'm now playing primarily upright, and wish the Mesa were cleaner. Is it possible to swap in cleaner preamp tubes and clean up my mesa? Alternatively, I've been using an eden navigator with a qsc/plx power amp that I like a lot. The Eden has a single preamp tube, and while solid state, it is definitely not "sterile and hifi." Can you guys help me find cleaner preamp tubes for my Mesa?