Do I have a dying tube? I've owned tube amps for years and never had a tube fail, so I'm not sure if the sound is what I should expect from a failing tube. Hell I used an SVT for over a decade without a single problem (other than it weighing so damned much). Last practice my new SUB Sterling didn't sound great and I chalked it up to a cheap bass needing new strings. Tonight my go-to US SUB sounded bad and a little farty. Swapped cables, new battery, same. Looked at the tubes, one of them is glowing blue, but in the way that online descriptions says is normal (photo 1): http://www.thetubestore.com/Resources/Matching-and-other-tube-info/Blue-Glow The tube glowing blue is the leftmost Sovtek 6L6WXT, and it's the only one glowing blue. The tube is also labeled 04 03, the next one 04 05, and the rest 04 03; I'm not sure what these numbers mean nor if it makes a difference at all. The preamp tubes, left to right, are 12AX7 (labeled MADE IN HUNGARY), 2 matching 12AT7 tubes, and a Philips 12AX7. I'm thinking about a set of JJs replacing the 6L6WXTs with 6L6GCs. There are other brands of tubes out there and I'm willing to listen, but some of the prices on tubes are nuts! I seek opinions and am all ears. Thank you.