My 1977 Ampeg VT-40 is still running the original Magnavox (re-labeled Sylvania) 7027A power tubes. That's nearly 30 years.

That glowing-hot scene is called red-plating. It happens when too much current flows through a tube, causing the plate to heat up so much that it glows. That will seriously shorten the useful lifespan of a tube. It was probably caused by a failure in the bias circuit that allowed the tube to run flat-out. Poor contact with the socket may cause this. But another likely suspect is a cracked resistor or a bad solder joint in the bias circuit. This condition could re-occur, and take out your tube(s).

You now have a power section with one fried tube in it, so you should replace all of them. Get a tech to thoroughly check out your amp, replace the power tubes, and set the bias.