Mystery Of Red Plating

My tube amp (ARC VT130) was blowing up her screening resistor on the left channel. The two Sovtek 6550 tubes would glow red- pulsating with red heat. If it weren’t so disastrously bad for them it would be fun to watch. I assumed it was a bias problem. I also

replaced resistors - more than necessary but as the story will tell not the right one. As it turns out it was bias- and a lot more! I had a resistor with a pin hole in it that was arcing to a trace on the printed circuit board which was pushing 100volts into a triode tube ( a 12BH7A) which is a voltage controller for the 6550s.

https://imgur.com/gallery/f9E1Yqd