[murf]

Hi Guy's and gals,
Have a Hickok model 800 tube tester that has developed a problem.
One day it started lighting the line fuse lamp on the panel when in tube test mode and while pressing P4 test button.
Any other test buttons depressed and no light on the fuse lamp.
Removed it from the case and noticed the 83 tube had some black ash like substance floating around in the tube.
Think the problem could be just the tube, or did something cause the tube to go bad?
Do I dare try to test the tube in my other tester, or would I find the tube is shorted out and cause a problem with that tester as well?
Any idea's?
murf