Swapped out some older JJ tubes in a pre-amp feeding a Parasound power amp. These seem to require a bit more warm up, and seem clearer on the bass than the JJ tubes. That's not a bad thing, as I think the highs are equally crispier through my AR speakers I can echo one of the other reviewers, they just seem louder all around. All in all, I'm impressed for the price. I wish I wouldn't have waited so long to change them out.