I did some comparisons of the KT66 tubes vs. several different branded EL34's, and a quad of 6550WD/KT88 Sovteks. In each case I much preferred the KT66 tubes over everything I have tried. I do not have any KT77's to try, nor have I heard a quad of those in a Dynaco before. If anyone has used a quad of the KT77's by Gold Lion I would certainly be interested in their opinion of that tube vs. the KT66.
I continue to be amazed at the clarity, the dynamics, and the overall depth of the sound I get from the KT66's even at volumes that I wouldn't really use. I mean loud, window rattling loud, and the KT66 tubes sound just fantastic. I cannot find any downside (except the price).
All my testing was done using Klipsch Heresey's. These old gals were made back in the late 60's I am told from the original owner who sold the speakers to me. Speakers are stock, birch plywood construction, original components as shipped from the factory. The amp uses an upgraded board I got from Kevin. The 7199's are old GE tubes that just refuse to die LOL. The rectifier is a JJ. The power trannie is an upgraded one from Heyboer, and the output trannies are original A470's. I am using a cap board in this amp from the Triode store. The original can is there but for looks alone. All my ST-70's run in Triode only.
I have listened to everything from ABBA to Zeppelin, and these tubes have performed better then any other quad I have personally ever tried. I have had no problems with the tubes, they are holding a bias of 1.26 volts on each side rock solid. I don't wash tubes, I just dust them off every once in a while so I don't know about the graphics coming off some have reported.
If any of you have a copy of the album "One Fine Morning" by Lighthouse, you won't believe the sound of the horns through these tubes. It made me laugh out loud when I heard the trumpet solo at the end of "Love Of A Woman". It was simply superb! Neil Young's 200 gram Greatest Hits was unreal. It was like Neil was in the same room. Annie Lennox on "Why" was unbelievable. When Melanie screamed out "Lay Down, Candles In The Rain", you could swear she was standing right in front of you. Freakin' Excellent!