I'm brand new to the world of tube audio amplifiers although it's fast becoming an obsessive hobby. The sound improvement over the stock tubes is astonishing. There's great stereo separation, a much wider soundstage, crispness and detail in the instruments/vocals and punch in the bass/percussion. And talk about headroom - I've never needed or wanted to go past the 11 o'clock position on the volume knob (driving a pair of Klipsch RM-15s and a small subwoofer in a medium sized room with vaulted ceiling). I've run these tubes about 30 hours over 4 days and they seem to be getting better and better with each use. Highly recommend this upgrade package.