Red Plating

[Jaymz77]

Hi all, hoping someone can point me in the right direction to start trouble shooting.
A bit of background…
I have a 2550x that i swapped a couple of caps in (just so all the caps were the same kind) and when i fired the amp back up i had a red plating output tube.
Now i thought i had traced it to a bad cap, because when i put the original cap back in the red plating went away.
Since then, i was rotating my preamp tubes when i accidentally dropped one of them onto a tiled floor. The problem is I'm not sure which tube it was. I think it was the PI tube.
It didn't break so i kept using it, but since then the red plating output tube has returned. I am 75% sure its the same socket that was red plating before.


My question is… is it possible that the PI tube is stuffed (assuming that is the one i dropped) and causing the red plating? Can a stuffed PI tube cause red plating output tubes at all?


Cheers