Went through several different 12AX7's in my phono stage (Hagerman Trumpet) recently that were loaned by a friend who has a stock. I liked the Tung Sol 12AX7's the best. Detailed, open with no grunge but still musical.
I also heard RCA black plate 5751's (2 mica version) and was not overly impressed. They definitely had lower gain but were fairly average sounding in my Trumpet. May be better elsewhere.
There was a Baldwin organ pull 12AX7 (not sure who made this and I've never seen it before) that had a lot of punch with an open and very clear top end. However, the mid bass was a little plumy and slow. But not a bad tube if you need a little warmth.
Bob
I also heard RCA black plate 5751's (2 mica version) and was not overly impressed. They definitely had lower gain but were fairly average sounding in my Trumpet. May be better elsewhere.
There was a Baldwin organ pull 12AX7 (not sure who made this and I've never seen it before) that had a lot of punch with an open and very clear top end. However, the mid bass was a little plumy and slow. But not a bad tube if you need a little warmth.
Bob