I replaced the Sovtek 6550s in my ARC CL-60 with Valve Art KT-88s. The VA are much smoother in the midrange and got rid of the harshness I had with the Sovteks. The bass is extended and clean. The highs are crisp without tizziness. YMMV with the Quicksilvers but I love the VA KT-88s so much in my CL-60 that I have not dared to plug in a set of Tung Sol 6550s that I got for fear of losing a good thing. I bought the VAs from DIY HiFi Supply for $25 each.Charlie
