It is the tube starting to go bad, though you should keep the tube in there to make sure it's not a one-time thing (unless the tube is glowing cherry red, then it's a goner). One year is about all I got out of any 6550s or EL34s in my JA80s before the fuses started to go, and that's what I'd expect out of the 200s as well; the only tubes that lasted longer (3 years and still going strong when I sold the amps) were the Gold Lion/GEC KT88s. Whatever you do, make sure you use fast-blow fuses; slo-blows will take out some resistors and give you that nice burning smell when they go.
Tube fuses on Jadis JA200 amps
Is there anyone that owns these amps that can tell me why the tube fuses blow. Does it mean the tube is bad? I retubed a little over a year ago and all of a sudden I've lost 3 fuses. I got 3 to 4 years out the last set(SED EL 34).I know the fuse filaments are microscopic. If I just replace the fuse it will hold for a while and then blow again. If I put a different tube in then the fuse holds. I know it sounds like I just answered my question but does someone have an explanation for me. Could it be power line surges?