I'm currently shopping for a used TIG. I found this one, it's exactly what I'm wanting. We have two of these at work and I've ran them a lot, but mostly stainless. Problem is the high frequency only works on continuous. I'm planning on using this for aluminium a lot. Main reason I'm buying one. But it's been a while since I've welded aluminum. Ours at work when I weld aluminium I leave the high freq on continuous, but I honestly don't know if that's correct.
Here is the add http://kpr.craigslist.org/tls/5161255998.html
Thanks