I have a VK30. Amperex all the way - I have 7308s in there now, but also had a bunch of 6922s which were equally as good (in some ways better. sold most of them - here on Agon.). Sovteks - bleah. There's so many better choices, Sovteks are the low common denominator at best. Forget Upscale, all you get are second-string crap from them unless you buy your gear there. (This applies only to 6922 and 6SN7 variants.) Some other dealers have the Amperex. Tubeworld.com has some, but pretty pricey. I will post more for sale if/when I find them. 6N1P is NOT an identical tube as the 6922. Not recommend using that, esp. when so many good 6922 choices exist. Check out Joe's Tube Lore at the audioasylum.com. early phillips are ok (50's-60s), but the later ones are not so hot. Since Amperex invented this tube (basically) it only makes sense to go with them if you can find/afford them.
-Ed
-Ed