When I was using my CAT "Ultimate" in my work I actually had a chart for swapping 6DJ8's and 12AX7's for both the phono section and line section. An amazing number of combinations can really change the sound depending on what you want. I love that about the thing. My 12AX7's are always Teles (the Ei is OK but just a Tele wannabe, IMO). The 6DJ8s I had (still have) for the CAT are the Teles as pictured above and a nice sampling of Amperex 6922, 7308, 6DJ8, etc). Fun times. Oh, and I have a pair of cryo'd EH 6922s that I sometimes use when I want an icy presentation (working on really warm stuff like EWF, etc. All good, I still love mine even though it's not in use right now. A great preamp, my only bitch about it is the noise floor using Amperex tubes is way too high, the Tele 6922 (E88CC) tubes lower the floor a lot.