Not "long time" (1 year) experience, but I have used a pair of EAT KT88 Diamond Valves in my former Unison S2K. They came at almost a quarter of the amp's price, but they heaved it into an entirely other league compared to the Sovteks the amp originally sported. Much - and I mean much - more transparency throughout the frequency range and authority in bass. Stabler image, better detail, yet a nicer musical flow without excessive warmth or roll-off. Just right. I also had the distinct impression the amp played louder at the same volume setting. When I sold the amp, I actually kept the valves, given what the buyer was prepared to pay. Tough luck for him. It was this experience with the KT88's that made me think not even twice when I acquired my present Audion 300B. I had to have EATs even if this time it set me back 40% of the price I paid for the entire amp including a pair of new Harmonix Gold 300B's. Same observation: in every musical respect now a better amp. With my gear - and that is as always an explicit caveat - EAT have been shure winners.
