In the Power 1, you can get more midrange bloom with Ei KT90 Type 3. Note we recommend them for the Power 1, but not the Power 2. We have also had a great experience with the Svetlana KT88 in that amp. Smooth and musical. DO NOT use the Tesla KT88. They have been very problematic. Then for even more confusion, there is a Chinese KT88 that looks just like the British classic Gold Lion. They were sold by Gold Dragon for a while, and have been unavailable, though we are supposed to get 100 or so soon. That tube is dependable, and sounds great with the little more extension at the tip top if that is what you want. Valvo never made a 6922. The ones you see being sold everywhere nowadays are older Tesla. We have some Valvo branded 6922 that are the real thing, made in Holland by Philips NV in 1964, but they are very rare.