Standard 12ga wire will carry 20amps with no problem if the amp is the only appliance on that particular circuit. If you dedicate one breaker to the amp, the wiring in the apartment should carry the load without heat build-up. Standard construction code usually requires 12ga wire, but I would check the guage of wire on the outputs of the breakers just to be sure.
Can you put a Krell in an apartment?
As you see I am a total "goner" living in a cheap apartment with about 50 grand in Audiophile equipment. I am looking at purchasing an old krell "FPB 400 CX" amp that the manufacturer says needs a dedicated 20 amp line. Can you still run this amp off a regular electrical outlet? If you can, will it sound like crap?