I think one of my 2a3's has lost it's vacuum, a milky white substance around the base, I think there is a tiny hole in the glass envelope around the base grid.

The filament does not glow, yet still appears to function, getting very warm/hot though not as hot as the other tubes.

I've noticed also the 2a3 next to it glows a bit brighter, could it be working harder to compensate for the other 2A3? Despite this it seems to be sounding just great, though possibly a slight imbalance but I'm not entirely sure.