Yep. Sounds like you have a bad tube. The plate is glowing brighter because it's drawing too much current, which blew the fuse (the flash and the pop).
Assuming it's a used amp: Replace the power tubes, replace the fuse and re-bias. Then you can get back to rockin'.
EDIT - If you plan to do it yourself, there's a thread in the forum
here on retubing an MA100H. The MA100C is very similar. And like Surf said, be careful.