Greg wrote: > What's the 'proximity effect'? It's an extension of the skin effect and has to do with current bunching caused by the relative proximity of current carrying conductors. If you can get hold of it, the Philips Technical Publication #207 "High Frequency Transformer Winding Design" has the best info on it I have yet seen. If you can't, send me your snail address and I'll be happy yo send you a copy. Malcolm