Loud pop right speaker, no right channel sound

Few speakers have fuses or reset protection, but Jason is right, especially if moving tubes make no difference, check the speakers, and move the amp's right speaker wires to the left. 

You can use any spare small speaker to get some answers, to see if a problem moves?

First swap speaker cables to determine if it is the speaker or the electronics.  very easy unless your speaker cables are exact length.

Figure out what the problem is before you try to fix it.

Thank you to all of you for the excellent suggestions for troubleshooting!   It was the right channel tube fuse. I looked back at my listening notes and the same fuse popped 2 years ago. This time it sounded much worse so I feared the worst.