[Phlogiston]

Here is the thing. An emissions tester of moderate quality/price will generally give you a good indication on small signal tubes. If you are dealing with power/output tubes for transmitters, stereo amps or just high power radio receivers (say anything bigger than a 45), you need a good mutual conductance tester. I would recommend the Hickok, in particular the 600A. They are not too expensive (yet) and will test the old big-pin tubes.