[miniman82]

Try an isolator/brightner first in case it's H-K related, if no luck see if a capacitance tester will give you any readings between elements. If so you can bounce the values off the tube data sheet for interelectrode capacitance, and if something jumps out at you as odd then try zapping that pair of elements. I doubt you'll have much success if that's the case though, at typical cap voltages you're not likely to see anything change. I have a tube here that took a microwave oven transformer to clear out, it had a partial short/leakage between K and G1. One momentary blast at 1600v fixed it. I was worried it would destroy itself but it's still working fine, it's a metal cone 8" tube in my Arvin.