GEC KT88 single-getter vs. triple-getter tubes


I recently received a Unison Research Sinfonia integrated amplifier and tried various tubes with it. As output tubes, I tried three-getter GEC KT-88 tubes which are great but I felt that they are overblown and rather fat sounding and lack air and HF extension. The stock tubes (Sovtek KT-88 marked "Unison Research") and somewhat lighter and brighter in a good sense and I thought I would keep them as output tubes, until I inserted the earlier vintage single-getter Genalex KT-88 tubes, which have more high frequency extension and transparency and don't have such excessive "bloom" I was suffering from. Has anyone had similar experience with these two varieties of GEC tubes? I will also appreciate any tips about a reliable source of NOS/NIB GEC/Genalex KT-88 tubes.
transl
You could also try the Chinese GEKT88, they are head and shoulders above other current production KT88 tubes i tried in my system.
They also are very affordable.

I did not had the chance to test a GEC NOS yet.
It's really hard to find these tubes now except on ebay. All tubevendors no longer have any of this stash.

I have a set which i cherish over the last 10 years...they lasts and lasts.

IMHO, these are undoubtedly the most natural organic sounding tubes that will give you that analogue or "LP" flavour sound.

I have tried Tungsols(NOS), Ei, Svets KT88 and 6550, GEKT88, GE 6550. GEC has proved the most reliable and lasting tube that i have tried to date. I have lost too many Tungsols and current tubes which just had heartstopping failure in my Conrads over these years.

There does not seem to be that difference as i had some single getters. Have you havd your tubes tested as the difference seems to be typical of wornout tubes.
Transl,
I have Unison Research Performance amplifier,it is same as Sinfonia beyond one Kt88 plus for each channel.
I am happy with Shuguang KT88/98 power tubes and for the 12au7 I could not find out any better than stock EH12au7s (I do not know it is because of this amps circuity or what reason?) and for the 12ax7s I have the best sound with both Ei and Shuguang 12ax7s.
I also replaced the stock icel brand capacitors (one 0.47 for each channel)with
Vcaps and made this amp much better.
Thank you, it's very interesting - about V-caps and everything. A year ago I replaced the stock 0.22uf caps in my Cary SLI-80 with V-caps and after a long, long burn-in (though their flavor was apparent at the outset) the amp opened up. Still, I believe thay are colored.