By not naming the phono stage, you have limited your responses from others who may have experienced the same issue. No equipment is immune from failure. .
Tube selection 12AT7 and 12AX7 - preamp
Sharing results of my internet reading..
This is all based on current production, no NOS or used tubes.
Best 12AX7. JJ ECC803S Gold pin
Best 12AT7 JJ ECC81 gold pin or Mullard new.
Should I select, 1. Balanced? $2 per tube 2. High Gain? $2 per tube 3. Low Noice/Microphonics $4 per tube? as offered by Tube Deport?
Any comments?