Moving beyond the *lame* discussion of serial numbers, I'd like to plug my favorite amp for the HD800 which is the DNA Stratus. The 2a3 is a great complement to the 800s. Directly heated triodes in general seem better than any smaller dual triodes or octals. They allow the 800s to retain their even frequency reponse while fleshing them out both up and down. The precise bones take on great body. The 2a3 is the best I've heard so far- better than the 300b. Next is the 45 when I get my BA redone. Any thoughts?
For me recently it is the F3 from First Watt. I am running it off speaker tops. Awesome bass extent ion and really even presentation across freq range.However currently the Stratus looks super appealing. As well as the GS-X mk2 -- having the preamp option on that one is a nice bonus.