Well, After I noticed that only 3 of the 4 poweramp tubes in my YBA200 were glowing, I thought I had a blown tube, or something fried. I took out the 4th tube, and switched its position with the third one, and voila, it would glow. When I moved the tubes back into there regular position, the 4th one would not glow. Also, only the first and now fourth tube glow blue. Is this bad? good? Is this some wacky tube problem? Do I need new tubes? For the record, the tubes are 2 Svetlana 6550c, 1 sovtek 6550c, and one winged c 6550. This is how it came from the guy I bought it from. It appears its the Sovtek that is glowing only in certain positions. What say you?