I decided to buy a selection of 12AX7 tubes to find out how they differ.
Remember to switch to 480p for better sound quality:
I tested the following tubes:
JJ ECC83 S
old used chinese 12AX7A
I tested the tubes by placing it in the V1 position, which is where 75% of the tone is made. the other 3 tubes (the last 25%) are Shugang 12AX7-B.
Settings on the rock master is ultra channel, gain pulled, max gain, EQ 3, -3, 3. The cabinet is close miced using an E906.
To get the same performance on all tracks I prerecorded a clip of dry guitar, and fed that to the rock master using a reamp box.
In my opinion, the differences between the tubes are negliable. It was however possible to reveal some difference by comparing two out of phase samples.