regulating welding current

[ottomobile]

Greetings, My question involves finding the most appropriate point to regulate welding current remotley on an older shunt regulated transformer type welder. I have added a high frequency generator and am tig welding with it but need to be able to regulate the amperage "on the fly" with a foot pedal or other means. Since the shunt must be loocked during welding, I will preset the basic range with the shunt, but must then make fine adjustments while welding to compensate for the progressivly hotter base metal etc. Can I regulate the input line voltage with a rheostat? Can I regulate the output current with a rheostat? Any help would be appreciated.
OTTO