I have owned the original 535, the MK2 and the B&K ST-140 with torroidial transformer. I really didn't like the MK2, it sounded dark and restrained to me, speakers at the time were the, likewise restrained, Celestion 100s, and the sprightly B&W DM 110s. The B&K seemed a bit strained and fizzy to me; I am definitely not a fan, but the rare, original version with frame transformer and lower power output should sound better. I still have a VanAlstine MOSFET 120B on which the design was based, that sounds just wonderful. The original 535 was the best of all, though foreword and agressive as stated above, it let go of the notes and had real slam and pace and better imaging as well. The funky speaker connectors can be a real issue though. I suppose that it all comes down to context and taste.
