Very natural sound, very lovely, a bit warm sounding, well built. VERY popular in its day and a classic. Make sure that your speakers are very efficient, or the room is small, and don't surround it with a lot of warm sounding gera as it's already warm. You want transparent cables and preamp to let the CJ present the beauty of the music to you.
BTW I usually prefer KT88's over 6550's but in the 11a and premier 12's (monoblock version) I ended up preferring the 6550. I find 6550's more neutral than KT88's and again, the 11a is already on the warm side.
The newer MV60SE might be good competition for the 11a (even that it's not considerd part of their "Premier" line). I don't see these often used though, or at the same price point.
Art
BTW I usually prefer KT88's over 6550's but in the 11a and premier 12's (monoblock version) I ended up preferring the 6550. I find 6550's more neutral than KT88's and again, the 11a is already on the warm side.
The newer MV60SE might be good competition for the 11a (even that it's not considerd part of their "Premier" line). I don't see these often used though, or at the same price point.
Art