What is the STR-430? I know that it's Russian-made. Some of the Sovtek 6L6 types have large oval plate holes. The STR-430 has small round plate holes. I'm guessing the STR-430 might be the Sovtek 6L6WXT+ or maybe the 6L6EH? Whatever it may be, I like the tone and need to buy a matched quad in the proper bias range for my for my stock 3ch Dual Recto. What do I need to get and where should I buy from?