Original poster: Teslamad-at-aol-dot-com Probably internal arcing. Most of those transformers are pretty well insulated though with tar and mica plating. Sounds kinda sketchy, but if it works good, use it till it dies. Sounds like you got a whole bunch for free anyways. Good luck! ~Drew <mailto:Teslamad-at-aol-dot-com>Teslamad-at-aol-dot-com