high frequency....use an aluminum setting,and brass rodsthat are available for O/A brazing...sand them clean with scotch-brite pad or sanding cloth to remove varnish/dip .... I have personally repaired several Airco Air arc whips, when the brass lugs were broken or burnt off....blow me if i'm wrong , but high frequency seems to be the only electric arc method that works on conductive and highly conductive metals. 