I used to do quite a bit of wielding many years ago. Even worked as a wielder inbetween electrical jobs. Fast forward to the last few years, and I finally got tired of paying the local wielding shop to do work that I was never happy with. So, bought a Hobart 140 off of Craigs list for a decent price. It worked great, along with my full size oxy/acet. torch set fpr several years. However, when it came time to fabricate everything to mount my Warn 18K on the A3, I found it to be a bit too lite. (rather short duty cycle) Would really like to upgrade it to one in the 180 to 240 range. (if someone wants to work a trade). In the mean time, I got a good deal on an old Airco 300 (made by Miller). It does AC/DC stick or TIG. Even has HF start, and a liquid cooled TIG torch. Back when I would wield for a living, this was the absolute top of the line. Did I mention that it is HUGE?
Have been seriously considering just using the wire feed part of the Hobart 140, and power it from the Airco for better penatration on the thicker material. The Hobart 140 was streatched to its limit on the 3/8 plate used on the Warn 18K install. Note, MIG does not do upside down wields very well. They get real ugly real fast. Next time, I'll do that stuff with the Airco on reverse poliarity DC and 7018 rod.
Remember to use straight argon on AL, with argon/CO2 mix or straight CO2 on mild steel.