Hi Bill,
I use a Hickok 6000A dynamic mutual conductance tube tester and mostly rely on the tranconductance value the tester reads out. The 6000A manual gives the Gm values which in most cases agrees with the RCA manual. The 6000A does have a Red/Green on the scale but I use the Gm value and replace a tube when the Gm is below about 60% of the book value.
73, Skip Magnuson W7WGM
