Howdy all, Thanx to all who commented on the coil I am presently building. Several changes have been made and the project is proceeding. Next question: I will be using 4 in. aluminum ducting for the torroid. How is this attached to the secondary?? I know this is a really dumb question, but, I thought I would go ahead and get the dumb questions out of the way. Thanx again George Stein