Tom, that is interesting. I may have been had. I built my K2 with "Rosin Core" solder. The manufacturer is listed as Jacques Ebert Associates, Glen Falls, NY 71542. When I bought the stuff I specifically asked for Ersin Multicore. It works great and makes great solder joints at 650 degrees. And, I might add, leaves very little flux residue. 73 Jim, W4ATK K2 #4028