Quite a number of amps have tube sockets that are riveted in. I can think of a lot of Ampegs for one, and a lot of Valco made amps, the Thunderclunker included.
It's quite simple for an old aircraft mechanic like me, but for those of you who are not used to this, do the following.
Use a spring loaded punch to put a small divot in the bucked head of the rivet-that's the round side.
Drill with a smallish drill so as to get a good pilot hole started. Then finish it off with a larger drill. I can't remember the sizes offhand but you can either punch out the rivet stem or use the butt end of a drill to snap the head off.
For tube sockets it's easier to make a little map of what goes where and then go ahead and cut the pins off with a pair of surface cutters. Then, once the new socket is installed clip the wires, strip them a little and reinstall.
Note the burned plastic on the old sockets.