Apparently EAR does not select those JJ 12AX7's! So just buy some new ones from your favorite supplier and you should be "good to go". JJ tubes have a good reputation for consistency!
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RAM Tubes Works, after testing/measuring their incoming tubes, grades and selects them for different applications. Their highest graded tubes for phono amp use are those which test the quietest, possess the best gain balance between the two halves, have the highest transconductance and lowest microphonics, etc. As Roger Modjeski is a tube electronic designer and manufacturer as well as tube seller, he thinks of tubes in terms of their specific application. He does not worship at the alter of vintage tubes, only at that of performance and technical excellence, feeling tubes cannot be evaluated without context.
I bought mine used but it a full set of Mullards in it which the original owner told me were original but old. It apparently was an early unit.
The sound was wonderful. I sold it to get an EAR 864 preamp which has the 834 phono pre built into it. Now I'm currently using an EAR 868 preamp with integral phono section which is a step up but not a big step. I'm keeping the 864 and switch to it every so often.
Hope this helps!