Hey Oldpunker (cool name !)
Tubes do where out and if you change them you may want to consider re-biasing them. I don’t know a lot about this however there are people at this site who do. Lordofthestrings is probably a good bet. This may do wonders for the tone of your amp. I had a friend who changed the valves on his JCM900, he nearly blew all of our heads up ! !