Battery Eliminator - any mains adaptor giving the right low rating voltage (12 volts?) will do although you you get better results from a 'regulated' one, the voltage will be more stable. Unregulated are cheaper but suspect for this sort of power drain. Maybe $50 for a regulated one isn't too bad - I paid £25 (about $40) at Tandy/Realistic a few years ago for a good one - if you get a variable output one you can use it for other things when you're not out gigging. Make sure the polarity (+ or -) is set for the amp.

The Solo will run quite happily off a 12v car battery (a bit big) or one of the sealed 'wet cell' motorbike or burglar alarm batteries (again 12v needed). From memory it will work at between 9 & 18 volts (although its efficiency varies). Again make sure the polarity is the right way round otherwise it will wreck the electronics.

Nick