Wiring Requirements for a Nema 5-20r Plug?

5-20 is a nema configuration. Since you have a plug, it is actually 5-20p. I am not at work so I can't verify it, but I assume it is 120v. If so, you need wire rated for 20amps, and a 5-20r receptacle, which should be 20a 120v. You can get these items at any hardware store or home center where they also should know local requirements and codes. I would put it on a dedicated circuit with it's own breaker to keep the current as clean as possible to help prevent distortion through the amp.

If it is a tube type amp, it will not be as sensitive to distortion as a solid state where harmonics come into play. Please consult an electrician if you have further questions or haven't done this yourself before. Err on the side of safety.