Tube Vs. SS Preamps

In fact, you ask others to describe the sound which you never heard, I will say it is very difficult. Usually on the forums,they all have some kinds of listening,and above of that,they exchange the comments.

I know your question,which is : After so many years listen on SS amp only,you want to explore something new,and see if the tube sound is better for you. right?

If that is the case,you gotten go and listening by yourself somehow and go back asking the question. That is the normal procedure,in my opinion.

"... the supposed advantages of tubes vs solid state audio. Among several listed reasons for tube gear "sounding" better was that tubes emphasize even order harmonics, whereas solid state emphasizes odd order harmonics"

Nelson Pass on two of his SS amplifiers: "It is perhaps not oversimplifying to say that the [Pass Lab] XA25 has a 3rd harmonic character and the [First Watt] F8 has a very 2nd harmonic personality," -- https://www.stereophile.com/content/gramophone-dreams-43-first-watt-f8-power-amplifier-page-2

running a nice class a amp with a very nice 6sn7 based tube preamp with a tube rectifier and have never enjoyed music more having tried every other option. 

biggest impact is the projection of the sound into the space of the room as if it were a floating 3 dimensional landscape.  

also a smoothness and naturalness to the sound with impeccable openness and transparency.  

never will i be without.  

What is "fatigue free" ?

Fatigue free, in my opinion , is talking of your ears, not the body.

Your body definitely will fatigue after several hours listening, however, your ear  is still enjoying  and want to have more time.that is fatigue free.