You sure it's not just part of the heater filament being more exposed?
Tung-Sol kt170 tube started glowing brighter
I installed 8 Tong-Sol kt170 tubes in my Sonic Frontier Power 2 amp. One tube started glowing a bright orange, yellow at the lower portion. I hear no sound interference. Should I replace it? If so, replace paired, right channel quad or all eight for matching purposes? I did swap the tube into different socket and it is the tube.