Results with the Beltron:
UPDATE: I reread the Beltron manual, something I should have done beforehand, and the "short light" is SUPPOSED to be lit the whole time. If it goes out, there is a problem. I had it backwards in my mind, I thought the light being on meant the tube had a short. My bad.
UPDATE #2: Still would like to know why a tiny drop in voltage brought the emissions down so unevenly. At this point, I'm going to assume the tube is good and just wait and see what kind of picture it will produce.