I listen to music daily for at least two hours a day, I spent 22 years playing guitar as a weekend warrior in so many bands I can't remember them all. In the old days I used to run an Ampeg stack that was tubed. I sold that for 50 bucks and bought a Peavey solid state rig. I hated carrying the Ampeg to gigs and rehearsals, it was so freakin' heavy. I'd give anything now to have that Ampeg back again.
I have 4 ST-70's in varying configurations, and I truly enjoy the sound from these old ironsides. All my amps have new power transformers, they all run in Triode, and the bias has been expanded. Two units use SDS cap boards and two units use the upgraded quad caps that I bought from Kevin over at Dynaco. I have one unit running 6GH8A's, one unit using a Triodestore.com EF86 based board, and two units running 7199's in updated boards following the original circuits.
I use a unit in the bedroom, one in the living room, and the other two I rotate into the mix every month or so. All 4 units are functioning perfect with no issues. I have EL34 quads of Winged C's, Mullard reissues, Svetlana's, and some old XF2's and internationals that came in amps when I first bought them. I also have a quad of Sovtec 6550ED's, and that's a good sounding tube also by the way.
As a side note I read that the Asylum guy named Jim that folks are getting the 6P3S-E's says that a bit over 12% of the tubes fail to meet his critique. He also says "that ain't too bad", but from a manufacturers standpoint that is really not good. I have 35 years in manufacturing and I know that if our failure rate ever went higher then 3% heads would roll. The cost of the tubes however is a fraction of the price of Gold Lion's, a hugh plus for the 6P3S's I think. I have read many good things about the sound of the 6P3S tubes. Certainly seems worth the risk to try them out at 50 bucks a quad.
I've listened to Zeppelin, Bobby Goldsboro, Little River Band, Steely Dan, Melanie, Janis Joplin, Traffic, The Eagles,Crosby Stills Nash & Young, and some FM from my Pioneer TX-9500 tuner....and I really like these new KT66's. I'll weigh in on the POSITIVE side for these tubes. I won't debate cost vs. benefits, I'll just say that I really like the tubes and I will buy another set of them. Thanks to all here for your hours of testing tubes and equipment, and your personal insight's into what you have tested and learned....}