Check out Sophia's website for more info; they are located in Virgina I believe. Supposedly they go to the Chinese factory and cull-out the best testing 12AX7's as they come off the assembly line. They are a little pricey in my opinion but overall they are the best 12AX7 that I have run across. My Hovland eats phono tubes for lunch so I am replacing them quite often; gets a tab bit expensive. I am in the hunt now for an end-all top shelf tubed phono; I've tried the Audio Research Ref Phono 2 several times and it was very good. Looking at trying the EAR 912 also.
http://www.sophiaelectric.com/
http://www.sophiaelectric.com/