Toroid Top Load Electrodes

My current top electrode is actually two separate toroids. One is permanently attached to the secondary and the other larger one is placed on top of the first. Here you can see the two in place on the coil:

The smaller toroid is formed on two 10 inch cake pans. I purchased the two cake pans and made a nice ginger cake with lemon icing before drilling holes in them and riveting them bottom to bottom. 4 inch aluminum dryer duct is wrapped around the cake pans and joined with fine wire like shoe lacing. I covered the joint with aluminum tape.

Again I used "Goop" to glue the duct to the cake pans. I made sure there was a nice electrical connection before applying the glue by removing the Teflon around the rims of the pans.

The larger toroid was formed on a form made from two sheets of masonite cut into circles. Blocks of wood act as spacers between the sheets of masonite.

Aluminum foil is glued onto the outer masonite surfaces before wrapping the tube around the form. I used brush on contact cement for this. Spray glue would work well as well. Spray or brush on the glue to both surfaces before applying the foil. Waxed paper can be used to prevent the foil from sticking while you position the foil. Once the foil sticks it is a done deal there is no repositioning it. Most wrinkles can be smoothed out easily with a stainless steel spoon. Use the smooth side of the spoon to burnish the foil.

The 6 inch duct is stretched out and wrapped around the form. If it is expanded carefully with one person on each end, you can expand it just enough to meet at the joint without having to cut it. I punched small holes about 1/2 inch apart around the ends of the duct so I could lace the ends together with dacron fly fishing line. This was somewhat time consuming but it made a nice joint. I covered the joint with aluminum tape and then glued the duct to the form with more "Goop"... I like Goop!