I have a set. They sound very good compaired to the stock tubes on my M520. Sweeter with better imaging with Cain and Cain abbys. They smelled like they were burning however so I removed them to see if it was my amp or the tubes. It seems like the insulators on the bottom of the tubes smells like they are burning, I have now put 40 or so hours on them and the smell is almost gone. For the money I think they are a very good buy. Matched quad for less than 80.00. Smell priceless
