This Quilter 1x12 combo amp is the HD version. Elsewhere people seem to think that stands for Heavy Duty. I personally think it stands for High Definition, as the speaker is upgraded in this model. Besides a few superficial scuffs this amp is in great shape. Super versitile. Super light. And it's hard to dial up a bad tone with it. 6 amp models. A variety of boosts. This amp will do everything from Jazz to Metal. Here are some words from Quilter's site. The Quilter 12 inch Mach 2 combo is the ultimate amp when you need serious power in a small package. Featuring a powerful Neodymium speaker, (Celestion BN12-300s) it sports 300 watts of power handling and a searing clean responsiveness with no speaker breakup or cone cry. A sealed enclosure calibrated to deliver a very balanced and beautiful tone, combined with the powerful and up front characteristics of the speaker are perfect for the jazz player or anyone who loves an EVM-12L type speaker response. It comes with big big bottom end and crystalline highs. Great for electric and especially hollow body instruments, the 12 inch HD combo packs a serious punch for players who love the sound of a 12 inch speaker, and want something powerful enough to handle a full band but portable enough to go anywhere. Combine this with our 12 inch extension cabinet for staggering power that will easily handle outdoor gigs without a PA system. Weighing in at 21 pounds, it is easy to carry and small enough to go anywhere.