The VK 31 uses six 6922's. That preamp does not use a 6SN7. Having said that I recommend the Amperex orange globe 7308, Holland made tubes. They exhibit great balance top to bottom. I owned the 31 for several years and for a mid priced 6922 the Mitsushita proved to be a great mid priced tube. Palpable bass and slightly rolled off on top.
BAT VK31 owner where are you?
Recently, I just bough a used Bat VK31 from another A'goner. It came with 6 Russia 6h23n tubes in it. The sound came out ok but would love to know what other tubes out there would made this pre sound better and where I can I find it. So far, I did contact Bret Jesse and he recommend me to look at some of the NOS 6ns7 from his website. What are your though? All recommend and suggestion would be highly appreciated. Thanks