I was asked by reader Brett, regarding Jackson 648, why is the setup data different for 6EU7 (“65XZ”) vs 12AX7 (“35WX”)?
Answer: This is yet another example of the inconsistency of tube tester setup data.
It goes even further, as 7025 has ~slightly~ different settings (32WX) vs 12AX7 / 7F7 / 6681 / 6SL7 / ECC83 (all of which use 35WX).
Basically… 6SL7 = 12AX7 = 6681 = 7025 = ECC83 = 6EU7 = 7F7 (loktal equiv).
All should use the same test parameters except for pinout and heater.
I would use “35WX” as the test config for all of those 12ax7 variants, based upon testing many 12ax7 successfully in a Jackson, and that setup config seems reasonable, and is the setup data used for most of the 12ax7 variants. I would say that the 6EU7 config “65XZ” is just a mistake by the engineer who created the setup data that day at Jackson.
I do not recall testing 6EU7 in a Jackson, although I may have back in the early 1990s because I had several Seeburg jukeboxes that used 6EU7 and I was using a Jackson 648A at that time.
Of course, tube testers are never perfect in their evaluation, regardless of setup data mistakes or not. I can show you many tubes that “test weak” on one tube tester or another, but perform fine in-circuit. If the circuit does not demand a lot from the tube, then “weak tubes” will often work perfectly fine for YEARS, even decades.
Often, a tube tester will drive a tube at-or-beyond its maximum design operating current, and a used tube may not be able to handle that “max load” as well as a new tube. But, very few real circuits operate a tube at its maximum operating current, which is why “weak” tubes often work perfectly fine in a real circuit.