I know this guy who is willing to sell ms a Marshall amp for 400 dollars. It is a JCM-800 tube amp with one 12 inch speaker. Other than one busted adjustment knob I've been told that it is in great shape. Since I've only been in to guitars for a year I don't know a whole about gear. I was wondering if there was anyone out there who could advise me to wether or not this is a good deal.