short in a tube-what happens?

Define a clear short.

6dj8 is a relatively common tube, to be on the safe side, I think if you know there is some kinds of short in the tube, then replace it with a good one. I assume the audio gear you have is expensive.

by short, I mean, my tube testers light lights up when it senses a short in the tube being tested.

the tube in question is a nicer SQ tube, so id rather not throw it away if it has some value.

A tube can short when heater wires within the tube deform under high heat and touch the cathode. Excessive heating happens when air leaks in the tube. With a heater to cathode short, excessive current can destroy an amp output transformer unless the mains are fused.