I would agree with Rcprince's observations. I have Cary slm 100's which can use el-34, 6550 or kt88. Harmonic richness is the el-34 strong suit, especially running triode, a little tubby on bass but the midrange and highs make up for it. I only use my GE NOS 6550's when I want to rock out, gives the amp a BIG sound, much more controlled bass. Otherwise I use SED el 34's for 90% of my listening.
