Bubz,the coil you posted the picture of I have seen first hand.It is made using a Magnetics EC52 type of core.Can't say what material for sure,but there were Magnetics E cores there in the stuff I seen.There were 4 rows of bifiller wrapped copper wire on it.There was thin cardboard between each row.Each row had @ 14 turns for each wire(28 turns total per row). So each wire had @ 56 turns.The wire measured .0425 inch.This coil was hand wrapped.Both wires were wrapped at the same time side by side just like the drawing.The wires ended on the same end they were started from.The start end of the wires went to the cell,and the finished ends went to ground on the pulsing circuit.
Hope this helps everyone interested.
Remember this set up was for the variable plate cell.
Don