Hello Jpms. I have both NU 350b's and Western Electric 350b's and cannot hear any differnce between them when used for regulator duty in the supratek. As many of you well know,the 350b was never really designed for regulation duty as it was traditionally used as an output tube, and when used as an output tube in an amplifier,it is without any doubt...the king of the 6L6 family of tubes. That said: I cannot hear any difference when used as an output tube either. Like most Western Electric vacuum tubes,the name itself will command premium money.If one can find the NU labeled 350b's at a decent price........grab em while you can! Hey gang..... It is like good real estate, *they ain't making anymore* Cheers