THIS PLATE CHOKE WAS DESIGNED BY MATT KK5DR. I BUILT ONE AND HAD GREAT RESULTS IN THE FIRST AMP. IT'S VERY SIMPLE TO BUILD, A 6" PIECE OF 1" DELRIN, A 1/2" X 3.5" PIECE OF IRON POWDER ROD, AMIDON R33-050-400. AND 5' OF 22AWG TEFLON COATED WIRE. THE PICTURES TELL THE STORY. THE CORE IS HELD IN PLACE WITH HOT GLUE. THE INDUCTANCE IS 180uH. THE COIL IS 3" LONG. ANOTHER SIMPLE PIECE YOU CAN MAKE YOURSELF.
UPDATE: ALWAYS MOUNT THESE CHOKES AT LEAST 2" AWAY FROM THE SIDE OF THE ENCLOSURE. CLOSE PROXIMITY TO METAL HAS A GREAT AFFECT ON THESE CHOKES