Glowing tube

[madialex]

I have a Crate V50 amp, retubed about a year ago. When I play it as long as I play very lightly its fine. As soon as I hit the strings a little hard, I can see one of the big tubes start glowing red all over and it makes a sizzle sound that gets worse as the tube gets hotter. I shut if off right after. Is this just a tube replacement or is it more going on?

[Zer09]

Have you switched the power tubes around to see if is linked to the tube or that socket? I would start there.