Adding fine adjust to Weldanpower 150?

[anickode]

Got a question for the Gurus out there...

Would it be possible to add a fine-amp adjustment to the Weldanpower 150? From what I can tell, the field exciter circuitry is similar to the larger weldanpower 225s. The "gears" on it are in 15 amp increments already, as opposed to the larger unit's 45 amp increments. Could I simply add an appropriately sized rheostat in series with the circuit to turn each setting into a range?

I wouldn't bother with an AC machine, but with the AC/DC version, it would be a nice feature to be able to really dial in the arc. Sometimes you just have that situation where 90 is just a bit cold, but 105 is a little too hot.