Tube amps and a Stradivarius

If tube microphonics are present, it is a problem not a feature. 

There’s always a degree of microphonics with vacuum tubes.

I have a quad of tung sol kt120’s (2018 m.d.) that are loaded with it.

Same year quad of jj kt88’s that barely sound when I finger flick them.

Im unsure how much it has to do with the “euphonic” sound of tube gear.

I always thought the 2nd order “harmonic distortion “ was most responsible for that…

The Neumann U 87 is still one of the greatest vocal microphones ever (tube). Records have a warm rich rumble that sounds great. Vocals don't have warm and rich rumble. 

Tubes are a physical effect mechanism that have nothing to do with accuracy. They are signal processing. Under Capital Records are 8 rooms, pie shaped with lacquer paint a Shure 88 microphone and a voice of the theater speaker in the corner, these are the most prestigious reverb rooms in the world but the equipment in their is not close to state of the art. 

Whether or not it is high second order harmonic distortion that adds richness or denseness to the sound, or there is something else at work, I like the sound of some tube gear.  I suspect that, in part, it is phase shifting in transformers that is part of the secret sauce.  
I have wondered about tube microphonics too.  I took part in listening to several different Western Electric 310 tubes that were going into a custom build linestage.  All of the listeners agreed on which tubes sounded best in the linestage.  The builder noted that we had picked the most microphonic of the tubes under consideration.  Whether this was merely a coincidence and we liked some other properties of the tubes or whether we liked them because they were microphonic is something that was not resolved.