Hi Superclamp, I think you and I met on another thread over this very same issue. I am a CAT Ultimate owner. Since the manual only says no US 6dj8's at positions V6 and V7, I would be very interested to know exactly what CAT told you is and is not acceptable at those positions. You and others on this thread seem to be suggesting that not only US 6dj8's, but perhaps all 6dj8's and all other 6922 equivalents (like the 7308/E188cc and the cca) and even 6922's from brands other than Sovtek (and perhaps Amperex or Siemens) are forbidden. I realize that I will have to give Ken Stevens a call, but considering the rather terse, and not very clarifying warning in the manual, your warning is not very understandable. Can you or perhaps anyone else who has specific knowledge of what is and is not allowed at V6 and V7 shed a very bright light on this subject. How, for example, could only certain brands of European NOS 6922 tubes be acceptable when this is not stated anywhere in the manual? I, too am a very happy CAT owner.