Thanks a lot for your help. I was accounting for some big hysteresis losses in a somewhat earlier design. So I guess the worst xformer design CAN have 70% loss :-). How does this look? Output: 12 kV, 500 mA Input: 240V, 60Hz Primary: 128 turns of AWG 10 Secondary: 6400 turns of AWG 30 CSA: 0.7853981633974 sq. in. By the way, what do you mean by TPV? -- --Mr. Postman (Doug Brunner) <dabrunner-at-earthlink-dot-net>