[RubberChipmunk]

Originally Posted by nate95366

Of course, I also teach science, and I read the "tubes were glowing blue" observation. I think you'd also observe that the tubes glow blue when the amp is on "1." The color only depends on the mixture of gases that have leaked into the "vacuum" (it's not a total vacuum). As the ratio of nitrogen to oxygen to argon and such changes, so will the color.

I have noticed this. It wasn't nearly as prominent at the lower volumes, and it tended not to last long enough for me to look in the back and see every time. When it was maxed, the tubes were quite obviously blue. Quite bright blue, at that.