hi i have a mesa/boogie bass 400+ which blew a couple of fuses the other night at a rather inopportune time. last night i had some time to fiddle around a bit and i have determined that one of the power/output tube valves is not working properly. all twelve output tubes were recently replaced by a professional, and i have verified that all twelve tubes are still AT LEAST good enough to light up, so i'm ASSUMING there is something wrong with the valve. it's the very first tube if you start counting from front to back, left to right (facing the rear of the amplifier) that will not light up, regardless of which tube i place in the valve. it powers up and passes a signal, sounds great, but it's going through fuses at a record pace. (yes they are the right fuses) does anyone know what might cause this? are there multiple possible reasons? i have tried searching online and i haven't managed to find anything that addresses this specific problem. at this point, i'm leaning towards selling the amp, though i absolutely love the tone. if i can pinpoint the problem and save the time and trouble of getting a pro diagnostic done before selling the head, that would be great.