Hi.
If You don't mind me saying this, any mic from the RS $5 cheapo upwards will do nicely miking the amp You have.
I'd go direct as well as the other guys who suggested that though, takes a lot of pain (or pleasure depending on how one views it

) off the process.
If You
have to mic it for a reason or another, SM 57/58 are hard to beat.
Regards
Sam