I would call Andy at Vintage Tube Services. You will probably need to tell him the brand and model of the preamp to maximize the value of his advice.
12AX7 replacement
It’s time to replace my tubes in my preamp. I’m looking for some suggestions as to specific brand performance and or where to purchase. There are a total of 8 all 12AX7. I believe 3 are for phono and the rest are for preamp and tone control circuits. Thanks in advance for your opinions.