I, too, went with Joe's TUBE LORE suggestions and have used the following with good success:
Sylvania 5751 3-mica
RCA 5751 3-mica blackplates (late 50's vintage)
GE 5751 3-mica blackplates
Am currently using the Raytheon 5751 w/windmill getter and really like it.
If you want to stick with the 12AX7 type, try the RCA 12AX7 long blackplates.
Of course, there's the "system synergy" issue which may be complicated if you have any other tube equipment in the signal path. Finding the right combination may take some time but will be well wotrh the effort.
Good luck.
Sylvania 5751 3-mica
RCA 5751 3-mica blackplates (late 50's vintage)
GE 5751 3-mica blackplates
Am currently using the Raytheon 5751 w/windmill getter and really like it.
If you want to stick with the 12AX7 type, try the RCA 12AX7 long blackplates.
Of course, there's the "system synergy" issue which may be complicated if you have any other tube equipment in the signal path. Finding the right combination may take some time but will be well wotrh the effort.
Good luck.