Up for sale is a pair of Sennheiser HD520 II headphones in very good condition with the original box. I purchased these about a year ago from the original owner. I'm not exactly sure how much use they've seen -- but given their condition, they either weren't used very much, or they were very well cared for. I probably put between 50-100 hours on the headphones in the time that I owned them. I can't find any significant scratches on the ear cups or headband, and the head strap and ear pads are in very good condition as well.
Based on the box, it would appear that this particular pair dates back to 1993. To me, the HD520 II sounds very similar to the HD600 -- similar tonal balance, but with a little bit smaller soundstage, and the treble isn't quite as clean (but still respectable). I find the HD520 to be more comfortable than the HD600 though, with less clamping force.
I'm asking $80 for the headphones. That price includes PayPal fees and shipping to anywhere in the continental U.S.
Thanks for your interest! Please feel free to PM me if you have any questions.