Hi Grimace
I have been swapping 12AX7 tubes with 5751 type tubes in a Jolida Glass FX tube DAC. The RCA Grey Plate 12AX7 tubes from the 70s I had in the DAC made the music very forward and cymbals and highs really had some sizzle to them. Music was borderline unnatural sounding. I rolled in some JAN GE 5751 type tubes from the late 80s and it made the music less in your face and calmed down the highs by wide margin.
I'm going to try to find Sylvania 5751s at a good price but they seem to be getting scarce. There are a lot of GE 5751 tubes out there for you to choose from. Lastly some tube sellers have low gain options for 12AX7 tubes BUT from what I've seen these are for newer issued tubes. E.g. Sovtek, JJ, Tung Sol. I don't know if that could be another solution for you.
Good luck.
I have been swapping 12AX7 tubes with 5751 type tubes in a Jolida Glass FX tube DAC. The RCA Grey Plate 12AX7 tubes from the 70s I had in the DAC made the music very forward and cymbals and highs really had some sizzle to them. Music was borderline unnatural sounding. I rolled in some JAN GE 5751 type tubes from the late 80s and it made the music less in your face and calmed down the highs by wide margin.
I'm going to try to find Sylvania 5751s at a good price but they seem to be getting scarce. There are a lot of GE 5751 tubes out there for you to choose from. Lastly some tube sellers have low gain options for 12AX7 tubes BUT from what I've seen these are for newer issued tubes. E.g. Sovtek, JJ, Tung Sol. I don't know if that could be another solution for you.
Good luck.