I have a pair of these tubes running SE UL in an amplifier designed for the KT150. At first I thought they sounded somewhat sterile, but after they had ~100hrs on them they really opened up and started sounding great. Bass is DEEP and very well controlled. Midrange is clear and forward, top end goes on forever and is rather delicate sounding (in a good way). Took a chance building an amplifier around this tube but it paid off. I'm very satisfied.