I recently was involved in a "wide open" test between JJ KT88's and Winged C 6550's. The main mule amp was a Morgan MP200, a pretty clean, straightforward circuit; it came from the factory with the quad of JJ's. My buddy bought the Morgan to use when his SVT rig is too much; we used his gig cabinets for the Reeves 400 tests.
http://sunn.ampage.org/sdp/index.php/topic,6005.msg25569.html#msg25569Anyway, he plays dimed, likes heavy power tube saturation, and wasn't at all happy with what he was getting out of the Morgan with the KT88's. Joe Morgan suggested 6550's, so he biased up a quad of Winged C's and fired it up. I thought it wouldn't make much difference, and they
were very similar up to the point that they started to saturate.
You have to remember the specification that these tubes were designed to; distortion was the enemy. The goal was to stay clean as loud as possible, and the KT88 was arguably considered the "king" of the big output tubes.
However, what we found was that at the ragged edge the KT88 was
too good. They certainly stayed cleaner louder, but they seemed to fight breaking up until they collapsed all at once, kind of harsh when they finally let go. The 6550's were much smoother going into saturation, and seemed more "musical" when they were totally wound up, easier to find a heavily saturated sweet spot.
Not what
I'm looking for in my amps, I like a big clean dynamic with a little grind, sometimes a little hairy, but not balls to the wall. The KT88’s suit me best, I run JJ’s and GT’s in my big Sunns, Gold Lions in my Reeves C225, but I have put a quad of 6550’s in one of my 2000S’s just to try it out.
As far as what’s best among the KT88’s I’ve used, The original GEC’s rule, the Winged C’s and the Gold Lions are very good for current production, GT’s have treated me well, EH’s are a little inconsistent in my experience, but I think JJ’s are just dandy; good sounding, reasonably priced and along with the Winged C’s the only KT88’s I’ve never had a premature failure with.
Probably the most important thing is making sure the
rest of your amp is healthy, the best tube in the world won’t cure a poorly maintained circuit. Spend your money making sure your amp is “right” before you drop a wad on fancy glass.
That’s what my experience has been, of course
your results may vary…
