I have tried Telefunken 6DJ8, Telefunken 6922, Telefunken cca, Telefunken 7308, Sovtek 6922, Amperex 6922, Siemens 6922, Telefunken 12AX7, EI 12AX7 and Tungsram 12AX7. I would rate the Telefunken cca's highest of all the 6DJ8 tubes, but for those for whom that is too bright, I would use the Telefunken 6922's. I did not like the Telefunken 7308's at all (too bassy, rough and unrefined). The Siemens and Amperex were somewhere in between. IMO, the stock Sovtek's were clearly inferior. I liked the Telefunken 12AX7's the best, although the EI's were very good and I could easily live with them. I felt the Tungsrams were rolled off in the bass. Generally, I feel that Telefunken's in the CAT Ultimate give great bass extension, great dynamics and a smooth, neutral, liquid midrange.
