Roger Modjeski of Music Reference and RAM Tube Works had for quite a while a forum on AudioCircle. On it he discussed tube amplifier design, tubes themselves, and the relationship between tube circuits and the performance characteristics of specific tube types---how the two are interrelated. The Music Reference Forum is no longer active (Roger has moved his business from Santa Barbara in Southern California to the Berkeley/Oakland area in Northern California, where he designs and builds amps, an ESL loudspeaker, and a subwoofer. He also teaches a course in amplifier design.), but remains readable on the AC site.
There is a LOT of information about tube circuits and tubes on the old Audiocircle MR Forum, well worth your time to peruse. Roger invented computer tube testing and matching, and is the world’s foremost authority on vacuum tubes. He’s not easy to reach by phone, but if you do you may be able to get a lot of your questions answered straight from the horses mouth.
