A YAMAHA B2 AND B2X AMP. BOTH OF THESE DUAL MONO CLASS A/B AMPS HAVE SERVED ME WELL FOR OVER TWENTY YEARS RUNNING VERY HARD TO DRIVE MAGNEPAN TYMPANI LOUDSPEAKERS. THE B2X IS REALLY CLEAN AND WAS BUILT FOR A VERY BRIEF PERIOD OF TIME DUE THE YEN SPIKE FROM 250 TO 150 TO THE DOLLAR IN 1985. IT RETAILED FOR 1500. THE B 2 IS THE SMALLER V FET AMP AND THE B2X IS CONVENTIONAL DESIGN THOUGH THEY STATE THAT IT TECHNICALLY STAYS IN CLASS A ALL THE TIME...IT DOES GET REALLY...REALLY HOT.