[gregb]

I have both types of testers, emission and mutual conductance. I find a person needs to understand his tester and it will serve you well no matter which type it is. The best tester is the equipment it is to be used in and you use a tester to make sure there are no shorts, there is some amount of emission and maybe do a gas test. With my emission tester I can tell if a power tube is good or not based not on the end reading but on how fast it gets to that reading. If it goes to 90 on the scale within a few seconds of testing, it will test great on the mutual conductance tester and most likely do the job in a set. If it still tests up in that 80-90 range but takes a couple minutes to get there it will not test good in the mutual conductance tester and most likely will have an issue in the set but not always. It will depend on what the set design expects the tube to do. A lot of sets are designed so the tubes just idle along without any real stress on them where as others have a tube running at its extreme limits. A weak tube will work fine in the first application but will fall on its face in the second.
Understand what you tester is telling you and what your equipment expects of the tube and any tester that is working as designed will give you usable results.

Gregb