Tube issues, 12at7 affect KT88?

Hello. I have a McIntosh 275V. I just tube rolled my 12AT7's. Started listening, and one of my power tubes, a Penta Labs KT88 went bright cherry red. I shut it down quick, let it cool down and swapped back. Looks like it's back to normal. Letting it cool down again and I'll swap tubes again and see what happens.

If it goes cherry again, what would make the 12at7 affect the power tube like that?

Thanks in advance,

Tony