Alright guys, was playing lastnight on my Valveking 100 half stack and the volume on the amp died really quickly and when i glanced at the amp one of the tubes was glowing blue.

I was too scared to leave it on incase it messed up so i ran to turn it off and now i won't dare switch it on.

Anyone know what this could be?

Dean Vendetta 4.0 "Tiger Eye"
Peavey Valveking Half-Stack VK100+4x12"