Speaking of toroids and top loads, what is the advantage of using two toroids, larger one on top with the smaller below? I see this configuration on may coils and don't understand the reason. Curt.
Curt, Using two increases the total capacitance which helps to produce longer brighter streamers. Also the bottom one behaves as a corona ring and prevents corona at the top turns of the secondary. Having this bottom toroid in place allows for placing the top toroid at a higher position which can help to throw the sparks out more horizontally which less tendency of the streamers to arc down and hit the primary, especially if the secondary is not that tall. Sometimes it's easier to find two smaller toroids than one huge one. Also the dual toroid system may be a little more compact in some ways.John