Interesting article, Dave, thanks. Where does the F-1X design fit into the various types of things that are listed there?
John, there isn't a lot of tonal difference with different tubes in an F-1X. The function of the tube is more about hi-fi sound reproduction than warm tube character. The F-2B has two tube channels which can be placed sequentially in the signal chain for more tubey warmth, and there are certainly other brands that make different use of preamp tubes.
As far as why Alembic chose to use a tube at all, I couldn't tell you. The benefits of the tube on the input stage over solid state are beyond my pay grade. I can tell you, though, that the F-1X is very highly regarded industry-wide for the pureness of the tone. If you have a great sounding instrument that doesn't need a bunch of coloration added in the preamp stage, then it's hard to beat an F-1X.
-bob
