Interesting, I rolled all my old 6sn7s (Sylvania vt231 bad boys, Ken rads vt 231s, NOS Tung sols, NOS RCAs and a bunch of others) but still stuck with the Siemens 12au7 in mine. It always sounds better than the 6sn7s I tried to my ears. Really like the rail idea. What's the third RCA for in your build? And what did you add next to the power cable connector there, I can't tell, looks like a 12V input maybe?