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5751 in CAT amps and preamps

I have been doing a lot of tube rolling in my CAT Ult MK2 and CAT JL2. I am working on the 12AX7 positions in both the amp and pre currently. So far the best combo I have found is the Raytheon blackplate square getter in the pre and the Mazda silver plate in the amp. Other tubes tried include: Amperex D getter, RCA black and gray plates (Square getter), Tung Sol square getter. I have used Joes Tube Lore for a guide and agree with most of his conclusions. I disagree with his broadbrush approach to the 12AU7 family. I think that there are many excellent 12AU7's and that it is definitely, generally speaking, a family with many more good options than the 12AX7 family. Joe is correct that most 12AX7's are unfocused to different degrees. I thought that the megabuck Amperex D getters were very good until I heard the American tubes. It was only then that I realized that the subtle smearing of detail was the Amperex.
The Raytheon is ultra detailed with lots of high end energy and good tight bass but can be fatiging. It is necessary to balance it further downstream with a smoother less aggressive tube. I was using the Tung Sol grayplate square getter and the RCA grays here (I think they are the same tube). This worked pretty well but some detail was lost and there was also some smearing. I then tried the Mazda and it is a very nicely balanced tube that works well as a smoothing agent following the Raytheon. The bass is not as pronounced as the Tung Sol but tighter and better balanced. The mids are not as fat and seductive as the Tung Sol but there is better detail with no smearing. I am pretty happy with the sound currently but am curious about the 5751. Any CAT owners that have experimented with the 5751 please respond. Bart


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Topic - 5751 in CAT amps and preamps - posbwp55@msn.com 20:38:54 10/24/06 (6)


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