Old 811A Coil
This old 811A coil was built my myself in 1975. It uses a conventional 811A pair with a feedback "tickler coil", a 1100vac / 500ma plate transformer and mica transmitting capacitors. The original secondary was damaged during a move and a new #26 AWG secondary was wound in 1979 on gray PVC pipe. The primary was originally wound on a cardboard tube. Performance, as I recall, was a measly 3" sparks. The primary plate coil eventually "slipped" down the tube and hit the grid tickler coil thus vaporizing the 811's! The coil was placed in storage and nearly thrown away many times. About 1990~1991 or so, my friend and I were at the Scottsdale Ham Fest when I stumbled across a pair of used 811A's and a couple of plate sockets sold to be by a blind ham radio operator. I re-wound the primary on an open form, re-tuned and immediately had 5~6 inch sparks! November 2006 I installed a 'Steve Ward' stacatto board. Same old 811A's and gray PVC secondary...8 to 9 inch mini swords!
on pictures to enlarge)