[J-rad2500]

I have an older machine that has amperage settings at 5 , 35, and 70 amps and then a current controll knob. What does the current knob do to affect the amps?

[MFleet]

Seems like you have the coarse adjustments listed. Then the knob will offer fine adjustment between these ranges.
i.e. set it at 5 and use the fine adjustment to dial in 5-34 amps.

A manufacturer and model# would help if you can find it or a picture.