A good way to check tubes for shorts is to hook your meter to the grid and the other to the filaments. Tap the tube and if your meter has a beeper on it, it will sound if there is a short while taping on the tube. Setting it on the ohms scale to read the short is often imposable due to the small time the tube is shorted. I learned the trick about the meter on the rig going negative with 4-400's tubes. Anytime I get an unknown tube, I test them in the way mentioned above! Sometimes people ask me how much a tube costs that I may have purchased. I tell them you have to add the price to the tube for all the duds that you purchased to get a good one. One caution, it's best to stick with Eimac. Most other brands are gassy! Glad I helped you
Another tip to see of you have a matched pair in there is to set you bias so the tubes are drawing about 125 mils and check to see if both tubes are showing equal redness, if they are not, pull the dull one out and try another.
If they are imbalanced, you'll splatter all over the band just as I did about a week ago on my BC-610D!
BTW, the next time I'm at my camp where the 610 is located, I would like to try to work you. What do you do up there? Freeze??