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.


With only 50 hours on the tubes why not try to get a warranty type replacement from seller?  It sounds like you were sold a bad tube.

I'm pretty sure you are seeing an event called "Red Plating" which is the tube overheating. There are a few causes- and finding them can be a mystery. 

The tube could be shorting (doubtful given what you've described)

The bias is certainly off. How could I know that? All biases are off at least a little. Add time, other component deterioration, and mismatched components and it's a boas nightmare. 

I had a mystery red plating problem and it turned out to be a bad 12BH7 high current driver - which caused me to have to replace 2 6550s. OUCH!