[ohohyodafarted]

Idealy, you can use a specially made adapter and test a 15GP22 using the same crt tester settings as any 21" roundie color tube, like testing a 21AXP22 or 21FJP22.

I made my own 15GP22 test adapter and generally use my Beltron as the tester.

However, it is true that if the tube is just slightly gassy, it can test good but not produce a picture. So in addition to using a tester, it is also useful to have a hand held tesla coil to see of you get a purple glow in the neck of the tube indicating a gassy condition.

I would first ask the person who has the tubes if the getters are still shiny silver/black? or are they milky white? If the getters are white, then there is no need to waste anybody's time to do any further testing. Send them photos of what good and bad getters look like.

Where are these tubes located?

I am not inclined to loan out my gear to people that I have never met with, or that I have no personal knowledge of. I think that's good advise to anyone reading this post. If I was to allow my equipment to be used, I would need to have first hand contact with the party needing assistance and be compensated for any costs incurred.