Some thoughts on tube rolling in the CAT Ult MK2 and CAT JL2. I have settled for now on Amperex 6922's in the CAT Ult and JL2. The cathode follower (v10) is a pinched waist Amperex 6922 PQ. I am using Raytheon 12AX7's (black plate square getter 1950's) in the pre. These tubes are ultra detailed with lots of high end energy and a tight punchy bass. If you follow this tube downstream (JL2) with the same tube listener fatigue will set in. I have experimented with the Tung Sol 12AX7 grayplate square getter. This tube has a fat luscious midrange combined with a fat somewhat overblown bass and rolled on top. It is not a bad combo but the Tung Sol smears detail somewhat.
If you reverse these tubes positions (TS in pre and Raytheon in amp) the wealth of high end and midrange detail is lost. I used to use the megabuck Amperex 12AX7's
(D getter 1950's) in both positions and I thought they were very good. It was not until I replaced them with the American tubes that I realized they were smearing the deatil. I then replaced the 12AX7's in the amp with Mazda silverplates (made in France). This seems to be a nearly ideal balance. The Mazda is a very well balanced tube that works very well with the Raytheon. It doesn't have the big fat bass of the Tung Sol but the bass is tight and in balance with the rest of the spectrum. It also doesn't have that seductive midrange of the Tung Sol but it doesn't smear detail and again the mids are in balance with the rest of the spectrum. When one area of the spectrum stands out it detracts from the seamlessness of the presentation. You end up listening to the parts instead of the whole. So it turns out that Joe of Joe's Tube Lore fame was correct about the 12AX7 tubes he tried.
They do lack focus. His description of a lack of focus is, I think, what I am describing as smeared detail. He just didn't try some of the best American tubes and the Mazda. I am using the Amperex 7316's D getter 1950's in the 12AU7 position of the JL2. The 12AU7 is a very good tube family unlike the 12AX7's. There are many good options in the 12AAU7 family and I have tried some that are good but the 7316's always edge them out. Here I think Joe dropped the ball and described this as a mediocre
tube family. I would love to hear more people chime in on this thread, especially owners of both the CAT pre and JL2, JL3 amp. Bart
