[Jukebox-list] Hot Plate (6973)

[Carl Haines]

This is more or less a curiosity question regarding tube failures.  I 
had my 220 playing for a little while with the back door open.  I poked 
my head around the back and noticed an unusual amount of heat coming up 
from the amp.  I looked down and noticed a red glow coming from plate on 
one of the "6973" tubes.  Since I recapped the amp recently, I figured 
the fault was with the tube.  I moved the tube around including the 
other channel and the problem followed the tube.  This "6973" is one of 
those National brand tubes that is a relabeled substitute and I have no 
idea of what the original tube is.  I know it is a sub since it has the 
strap on the bottom to connect the appropriate pins.  I have pulled 
these tubes to prevent any damage and ordered replacement Electro 
Harmonix 6973 tubes.  Now I am curious as to the failure of this 
particular tube.  Does anybody have any thoughts or guesses as to what 
happened with this tube?  Was it unsuitable substitute due to have a 
premature failure?

Carl Haines