http://www.diyaudio.com/forums/solid-state/162081-dc-servo-mosfet-amplifier-20.html http://www.diyaudio.com/forums/solid-state/162081-dc-servo-mosfet-amplifier-19.html Amplifier for 1R load 2SK135/2SJ50 and MJ15024/MJ15025 can be used instead 2SK1058/2SJ162 and 2SC5200/2SA1943 for FB400 Speakers used with this amplifier will be between 1-3 ohm ( full range ribbons)