Some tube manufacturers specified a maximum grid leak resistance. It was
often about 2 million ohms. Drake found that much higher resistance was
great for avc performance.

However, over the long run, it was also asking for trouble.

In theory, what Chuck says is true - that transconductance testers are
better than emission testers. However, I can just report that in hundreds
of tests I have just found a couple of cases where there was any practical
difference.

I often end up getting sucked into helping others get their receiver going
again. I do not charge for it and I want to get back to my own projects.
The emission tester is much faster to use and I do not really care if the
tube is 79% good or whether it has 10% less gain. The radio does not work
when I start and I am looking for black or white, not shades of gray.
Often, it is not the tubes, but rather another component. The tube tester
simply eliminates the tube as the culprit for total failure.

I suppose if I were looking for a tube with the best performance for a 2
meter moon bounce preamp, I would use a transconductance tester. However,
in that case, I would not use a tube at all.

I could not imagine running all the tubes of an S-85 through the test
procedure for a transconductance tester - unless I had to.

Colin K7FM