could you check it?maybe the filament voltage is too high.
Ok I tried all of the tubes that I had to hand, unfortunately I threw out all of the dead tubes a while ago, so apart from one tube all of these worked ok, all tubes have a tiny constant glow while working
so left to right:
2 x mesa tubes, these sound ok if a little flat, even though I bought these together they are a different design inside?
next with the green print, Jan 12AX7WA, this one sounds quite full tonally, but noticeably less gain
2 x Chelmer Cvc Ecc83, these are the tubes that were installed in the MP1 Classic when I got it,
for some reason I thought these tubes were plain with no markings doh!
these tubes sound fantastic, now I know what they are I'll get some more, incidentally these look very similar to the Mesa tube far left in the picture,
lastly is a Harma Cryo 12ax7 from Watford Valves in the UK, I bought a few of these and they all failed including this one, it still kind of works but the output is low and it crackles and farts, I wouldn't recommend these to anyone,
from what I recall, other tubes that died in the Classic were a couple of Groove Tubes 12ax7 and a jj ecc83, there were others but I can't remember, however all of these tubes worked fine in other gear?