Many people believe that a tube tester needs to be a transconductance type
to be accurate. I have numerous examples of both.

My experiences through hundreds of tests are that the emission tester is
accurate in almost all cases. As a matter of fact, I usually grab whichever
tester is handy. If a tube is bad, either tester will usually tell you.
Emission testers may actually be better in some situations - such as
determining life left in the tube.

I can recall only two tests in hundreds where the transconductance tester
led me to a problem hidden by the emission tester. In one case, a Drake
transceiver had a tube that had developed cathode interface and had about a
1 megohm internal leakage, which had developed because of a circuit designed
by Drake, which had a very high impedance grid circuit that recommended by
tube designers. Although I had substituted another tube, it also had
cathode interface. The transconductance tester allowed me to do some
detective work to find the problem. A third tube solved the problem.

In the 30's, many people built their own tube tester. I have done that.

I may get a lot of flack for my opinion, but I have my flack shield on and I
can only report what I experience.

Colin K7FM