On Mon, 17 Oct 2005 00:39:48 +0000 (UTC), Cydrome Leader
wrote:

The physical case sounds really large for such a capacitor, especially a
mica one.

Induction heater polypropylene caps might be an acceptable replacement.

Does anybody know what frequenecy these welders operate at, and possible
RMS current levels these caps see?

The freq is typically somewhere between 1 and 8 MHz. You can
figure the RMS current from the voltage level and freq. That rating
would be very conservative because it's basically like a Marconi spark
xmtr rather than a CW-excited tank at the operative freq.