Miller Dynasty 200 DX, Inverter technology can be run on nearly all possible voltage inputs it can run off a generator. I have one of these and it is going to be topped out before you get into 100% penetration on 1/4" but it'll be a great learning machine. It has frequency adjustability, pulse, and its really cool!
Peace,
pjseaman
Thermal Dynamics has come out with a small TIG machine (DC only) 85 amps. It should work for what you are doing with copper. It is inverter technology, about the size of a lunch box and can stick weld with 3/32 rods from a 110 volt outlet. The drawback is you will have to make a pigtail for the plug because some well meaning engineer put an odd shaped 110 volt plug on it. I think that the machine is around the $500.00 price range. I saw one demoed and it was pretty impressive. I would get one but I already have a Miller Dynasty 200 DX.