I’m very much enjoying my new DarkVoice 336se tube headphone amp, and part of the fun is rolling in different 6SN7s I have on hand with my Sennheiser 6xx cans. Perhaps it’s folly, but I do think I detect differences in sound depending on the tube. Ken-Rads tend to have deeper bass, RCAs are darker, Sylvanias as brighter. I’m talking different 6SN7s, not substitutes. So, in Objective Land, has anyone measured the effect of tube rolling? Do measurable difference show up when it’s looked at?