I finally finished up my Ampex 6973's mono blocks and am running them through a Sound Valves 101 6 tube 12ax7 cathode follower preamp and finishing off with Klipsch La Scala's .It's unbeleivable the power these little 15 watt amps put out . I have NOS RCA tall bottle 6973's and new 12au7,and el81 ,power supply bypass with poly caps,all new wiring ,sockets and you know the story. 1/3 volume will take you out of the room,incredible little mono block's .