You can get a HF box for TIG welding. This just gives the high frequency and perhaps a gas selenoid depending on which one You get, but does not give uou a contactor or remote amperage controll. For My point of view, You would be further ahead buying an old Miller A/BP 330 or a Lincoln 300/300 tig welder. These often sell for about the same price as a HF box on eBay or Craigs List, and have all the features You need for most work. Another cheaper alternative for DC tig is to get a torch with a built in gas valve and scratch start it. This does limit You to DC operation only. I don't know of any add on plasma units.
