When is a tube out of range? Tubes have a large number of operating characteristics and parameters, as well as the different physical and mechanical bits. Circuits can have some range, more and less, of operational latitude to operate a tube under.
I bring this up around a specific curiosity of the Crack's output tube. The 6080 and 6AS7G have identical electrical characteristics, and they differ in packaging. I see the 6H13C and 6H5C (using Cyrillic here) typically called, or often treated as, direct substitutes for each other and to the 6080/6AS7G. They all look very close on the datasheets. Calling out the Gm, the 6H5C is quite a bit lower than the others - 5,000 vs. 7,000. What difference might this transconductance difference make in the Crack?
What prompted me to post this is someone mentioning to me recently that they've heard people report the GEC 6AS7G sounds as good or better than the Western Electric 421A/5998. Looking at the data sheet, the WE 421A has a Gm of 20,000. Isn't that a large Gm difference from the 6080? Could the tubes be direct subs in the Crack?
I really like the SED 6H13C and 6H5C. I can't hear a difference between them.
