General consensus says RCA RED BASE, and Sylvania VT-231 are the best sounding tubes for the MFA. Not having heard the MFA with these tubes in it, I cannot say. But these tubes are pricey. Manufacturing quality was routinely very good in the 30's, and 40's, that I would hazzard to say that the Westinghouse, KenRad, and most American 6SN7's will sound very good. So I would purchase some of these, which are very reasonable, and see if I even cared how the others sounded.