NOS RCA 21AXP22 Color CRT on ebay, Item number: 6192055949. The seller wrote "This tube is in the original box and checks excellent on all three guns." But the crt meter on the photo checks only good in the lower end of the good range.

Hmmmm.... this should be fun to watch. Foutunately, I have a spare, so the pressure is off.

I'd ask the guy what the actual scale readings were on each gun and what tester he is using. I tested the 21axp that's in my ctc-5 for the heck of it once on my late-60s RCA tester and they all tested WAY over on the right end of the good range. But maybe difference between good and excellent isn't that important an indicator as far as how much life a tube has left, brightness etc. ( ? ) Or is it?.....Frenchy