Why do Tube Amps sound more romantic v SS amps

In my view, a lot of this discussion gets sidetracked by ambiguous language.

If two people sing an octave apart -- or a 5th apart -- it sounds lovely, doesn't it? Would you call that "distorted", from an aesthetic standpoint? Probably not. But compared to a single voice, it is "distorted" from a technical standpoint.

It's weird, isn't it for something that sounds mellifluous and pleasing to also be distorted? That weirdness comes from the ambiguity of the aesthetic meaning of "distorted" and the engineering/measurement meaning of "distorted." But they're not the same thing.

Is a tube amp distorted, then? Technically, "yes," and aesthetically, "no" -- if you like that kind of aesthetic effect.

Here's something useful from Tung Sol:

"The harmonic content of an overdriven tube amplifier consists primarily of 2nd order and 3rd order harmonics with some 4th order harmonics. The harmonic content of an overdriven transistor amplifier is primarily 3rd order with suppressed 2nd order harmonics. 2nd and 3rd order harmonics are the most important from a viewpoint of electronic distortion. Musically the 2nd harmonic is an octave above the fundamental and is almost inaudible, yet it adds body to the sound, making it fuller. The 3rd harmonic is a musical 12th. Instead of making the tone fuller, a strong 3rd harmonic makes the tone softer. The odd harmonics (3rd, 5th, etc.) produce a "stopped" or "covered" sound. The even harmonics (2nd, 4th, etc.) produce a "choral" or "singing" sound. Adding a 5th to a strong 3rd harmonic give the sound a metallic quality that gets annoying in character as the amplitude increases. A strong 2nd with a strong 3rd harmonic tends to open the "covered" effect. Adding the 4th and 5th harmonics to this gives an "open horn" character. The higher harmonics, above the 7th, give the tone "edge" or "bite."

https://www.tungsol.com/html/faqs14.html
 

Also what I have heard and read, I agree with several in this post that It’s all about the “good” distortion that tubes produce. Pleasing to the ear. 

I think it depends on your definition of "romantic" and other factors, such as personality types, venue, and where the specific "romantic" element is positioned on the classic sine wave of the evening's total love-making cycle.

I'll give tubes a definite advantage during dinner and foreplay.  After that, there are simply too many varibles to reach a solid conclusion, IMHO.  I'd use the common "thumbs up" term here for vaccum tubes but there are, most likely, other things that are "up" during this segment besides just thumbs.

The age and energy levels of participants could swing the pendulum one way or the other.  Also, whether one is an analytical chess player, or a "score right now" hockey player could be factors..  As for intensity, I can't explain why but the terms "slew rate" and "dampening factor" pop into my head, giving solid state the advantage.  And, yes, the venue.  An AirBNB is quite different than tent camping (both of which have zero chance of having a vacuum tube amplifier near by), so a solid state (most likely a Bluetooth speaker) will be the winner by default.  

In summary, I tend to be neutral on the tubes vs SS debate, and I'm sure either can rise to the occassion when called upon.

Everyone always brings up the distortion profile of tube equipment, which is generally true but triodes are also more linear that solid state devices, with simple designs fewer parts count.

Let us not forget that ALL recordings are PROCESSED and have some relationship to the actual "live" performance, but not all of it.

In the "old days," this processing took place on TUBE recording gear since that was all that was available.  When more sophisticated recording equipment became available, many times it was solid-state based.

SO, any recording you are listening to has the "imprint," if you will, of the recording engineer, the producer, the band members or orchestra director, and possibly others (marketing) in its final form. 

A simple example would be that in the 1960's, "pop" recordings were "mixed down" so that they "sounded good" on car radio speakers, which, in those days, were not exactly designed to reproduce accurate performances, but instead were going for a "sound" that would "sell."  (Buddy Holly is credited for "producing" his own music because he did not believe that a record company producer could create the "sound" that he had in his head.)

This is not necessarily "good" or "bad" but it is anything but "accurate."  About the best you can do for that is to get some master tapes, which, if modern, have been "mixed down" from 64-tracks (possibly) to 4 tracks to play on a home reel-to-reel deck.  You might also want to play some direct-to-disc vinyl recordings like those made by Lincoln Mayorga et. al. in the 1970's.  There are probably others out there as well, but this is a difficult and expensive process, so you don't get many and yes, even those are "processed" to some degree.

So, buy what SOUNDS GOOD to you IN YOUR ROOM and don't worry so much about the electronics.  For ME, personally, ARC tube HW playing through properly set-up Magneplaner speakers is the closest to "accurate" when reproducing processed music.  Everyone has their own idea of this, thus the myriad number of companies producing home audio gear.

Cheers!