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Old 13th January 2020
Gear Head

Superior Instruments Co. Model TC-55 tube chart confusion

I dug out my old tube tester to test some tubes, but the tube chart is confusing for some of the tubes (the best ones). I am in no way a tube expert (or even tube novice?) My tube chart is a pdf of the June 1958 printing. it's a bit smudgy in places, but I'm happy to have it. I want to test 12ax7, 12at7 and 12au7 tubes (also 5751). Each of these have 2 listings, and all of them are the same except element slide switches for plate position. So this is basically what I'm looking at (hope tabs spacing holds)

{tube / fil. volts / F / N / P / sens. / fil. cont.

12ax7 E 4 9 2 35 4,5
12ax7 E 4 9 7 35 4,5

I assume the difference in "P" of 2 or 7 is for testing each of the plates, although I have noticed not all in the list have 2, some are 1, some are 3 (maybe more?) [a 12BR7 has 3 only difference is in P and sens.] [while a 12BL6 only has 1 listing] again, not a tube expert, but I'd rather be sure about my understanding on this. (does a 12BR7 have 3 plates???)

Second question, and it's kind of 2 for 1... 12ax7, 12at7 and 12au7 all have the same listings. My "understanding" tells me yes filament voltage should be the same, so even though my list does not reference a 5751, would I be ok using these same parameters? If not, why aren't their any differences between 12ax7 and 12au7 in the list?

Sorry for the noob question, but my documentation is very limited, blurry and smudgey for this old unit. Final Q, are there any good books I should have referenced first? Not so much a "Tubes for Dummies" but a "Tubes for the ignorant or uninformed"