Differences in SQ between EL34, KT-88 & 6550 Tubes

I would differ to Albert since he's sp[ent much more time intrenches but I had thought that the KT88 provided more in the bass region and had more dynamic slam.6550 has econonomy going for it and EL34 was the best for midrange perfecty for coherent two way monitors where the midrange is the thing to be accentuated with it's warmth and timbre.But again amp makes big difference.New mac amps use the KT88 to full advantage and are designed to do so though again the roll is most expensive of the 3.
Chazzbo

My experience has echoes Newbee's and Albertporter's. You might consider an amplifier that allows you to use any of these tube types. Then you can switch between them, depending upon your mood. Quicksilver Audio offers this versatility with some of their amps, and no doubt others do as well.

I echo what Newbee wrote, the generalizations he made match my experience with these tubes. I would only add that the 6550 seems to produce the best very low bass, at least among the amps I've auditioned.

So much of the SQ depends on the amp the tube is used in that any comments have to be very generic and unspecific. That said,

I have found the EL34 usually has a warmer mid-range than the other 2, the KT88 has a warmer upper bass/midrange and a tad more sparkle in the highs, and the 6550 is the more neutral of either providing a uniform response through out the range.

Much of which tube/amp combination you prefer will have to do with your speaker/source selections and the brand of the tube, they vary substantially within each type. As you will see, others with different amps than mine will have varing opinions. There is no pecking order - each tube will have its own adherents.