BloomingtonMike:
The HF unit is for AC TIG. Rob is absolutely right. HF used with conventional stick, well, if there is any conductivity between you (as in body) and ground, you will become the electrode so to speak. It could be very unpleasant, maybe even fatal.
I have the HF unit on my AC/DC Lincoln gas unit. It's for TIG only.
I believe the later model Hobarts and maybe the Lincolns have a process switch for that use. Mine don't, they leave it to the operator. /forums/images/graemlins/grin.gif