marty_e,
On my ARC D115 and Jadis 200 amps, the stock tubes were GE6550s. I feel the sound
of these tubes were punchy and a bit lacking in warmth. Highs are clean and fast, and
can tend to be a little hard on some bright softwares.
I had read MrDick Olsher of Stereophile say that he does not consider 6550s as 'audiophile'
tubes, but rather, one should use the KT88s instead. From that time on, I had been longing
to try KT88s. At that stage, only made in Shuguang KT88s were available at affordable
prices bec the Richardson ones were like 10,000 pesos each. But a friend told me the
China KT88s were terribly bright and thin sounding. So I lost interest.
My chance came when the SED KT88s went on the market, at about $40 each. And I
bought 8 for my ARC VS110 amps. The VS110 has stock 6550 tubes made by Electro
Harmonix, which are shaped like KT88s. And I must say that these tubes sound not
like the GE6550s in that these are now smoother, and not hard. And hi's are well
extended and not bright. When I replaced them with the SED KT88s, the overall
sound became more laid back, and also a bit soft and mellow. The word I can think of
is 'refined'. Everything seems to have more 'class'. Strings are sweeter and without
edge. Bass is less punchy and tight than the EH though. And the midband is where
these KT88s really sing. It makes good recordings sound even better. Overall, they
are excellent. On soundstage, both are evenly matched, though the KT88s seem to
project a slightly deeper stage. I like them. And sorry, I had never tried KT90s.
At this point, I am very happy with the SED KT88s. I wish I can
afford the GEC Gold Lions, but maybe I should buy one each year till
I hit 8 pcs.