Been using mine for almost a year now with the TH-600s and its a match made in heaven. They will have to pry this thing from my cold dead fingers when I go. The standing 6SN7 thread is a gold mine of information. The RCA VT-231 and Westinghouse tubes(15$) are a great synergy with this amp too. Tun Sol BGRP are another favorite of mine, but finding them at a reasonable price is tough.