Have you biased your tubes? Is your amplifier capable of accommodating the KT170? @ozzy has a point and KT120s maybe better suited for your application. I have had no issues running any of the KT series valves, 88, 90, 120, 150 or 170 as my amplifiers are built to accommodate operation with any of these tubes. Have you tried swapping this tube in another hole to see if it lights up like it is in the current position. If so it may be a bad tube. If not check you may have other issues.
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.