Are tubes really “warm”?

Not necessarily. I’ve heard certain tube circuits and/or certain tubes that could peel paint. On the flip side, some badly designed/implemented tube amps can have massive roll-off and gobs of THD, and that can be used to perpetuate the stereotype of "warm, rich tube sound", but it doesn’t have to be that way. Certain tube headphone amps and cheap Chinese tube amps can be particularly guilty of either kind of bad tube sound - but is that stuff really a proper "tube amp" or should it be thought of more as a novelty? Really good tube gear should be reasonably neutral with THD at least somewhat under control, and featuring good extension on both ends.

     I’ve always enjoyed the sound that tube preamps and amps impart on the overall sound of a system. It’s my understanding that, when tubes and tube equipment begins to distort, they do so in a manner that results in an excess of even order harmonics being produced and added to the inputted signals. As opposed to when ss circuits and ss equipment begins to distort, they do so in a manner that results in odd order harmonics being produced and added to the inputted signals. 
     In general, humans tend to perceive the added dose of odd order harmonics as strident, bright and unpleasant and the added dose of even order harmonics as sounding pleasant, with added body, tone richness and a sense of added dimension to stereo sound stage illusion images. I’ve always found these qualities pleasurable too, thought the term ’warmth’ referred to all these specific qualities in total and initially thought tubes had to be present in the audio chain somewhere to attain these qualities in my various audio system configurations.
     For many years I used a VTL 2.5 TL tube preamp, with a custom set of four NOS (new old stock) Mullard tubes swapped in to replace the VTL’s stock set of four Russian or Chinese tubes, in combination with a series of high current ss class AB amps from Adcom, McCormack and Aragon to achieve this quality of warmth in my systems.        These combinations of a tubed preamp with a ss amp were all very good; providing adequate power to drive my inefficient pair of Magnepan 2.7QR main speakers, providing good bass along with detailed, smooth but never overly bright midrange and treble performance with just a touch of added warmth.
     However, I have to agree with others on this thread that mentioned there are rarely absolutes in this hobby. I suggest that particular component combinations need to be auditioned prior to claiming any overall system sonic results with any specificity.
     For example, my current system consists of a ss Mark Levinson 326S preamp combined with a pair of high powered class D mono-blocks. My overall system sound is very similar to my former systems using a tube preamp, including the touch of warmth. But I perceive the ss 326S as having additional strengths, such as improved bass performance, a lower noise floor, improved detail, a more neutral presentation and a much improved stereo sound stage illusion ability that is more dynamic and spooky realistic on good recordings.
     I now believe that good body, tone richness and a good sense of dimension to stereo sound stage illusion images are more a function of the qualities of the music, the quality of the recording and the quality of the reproduction system as a whole rather than the inclusion or exclusion of tubes in the audio chain. I believe absolutes in this hobby are best avoided.

Tim

@noble100   

and the quality of the reproduction system as a whole rather than the inclusion or exclusion of tubes in the audio chain.

+1....you said it so I didn't have to. As if all you're listening to is a tube...ha.

Newer VTL, and AR both sound like the older Krell, to me. Nothing warm about it.  Citation II, MC30, Marantz #7 and 9s that's the warm sound of valves people refer to. When folks say it now, I doubt a lot have heard the old valve sound. Like noromance said. Different parts, and a lot tighter tolerances, now.. 50 years ago... They ran WARMER too, oh my...... LOL

Regards

 I believe absolutes in this hobby are best avoided.

@ Nobel100, well sure, in general, ss amps display a  characteritic, which tube fans have no desire to ever go back to. 
Speaking of ARC, I've only heard a  ARC system with a  speaker that may have colored, in fact no doubt did color the sound. 
can't reacll the big tower speakers,, He had  a cary 303 cd player
I did not like the sound. 
As I say, i recently auditioned a  hefty tube pre (retails @ $3K+) , i do not want to call out the brand.  But just did not synergize in my system (lame excuse). Maybe one of the other models has superior sonics, i have no idea, Not willing to chance it.
But I do know fora  fact  there  does <<NOT>> exist any ss pre amp in the universe that would even comke close to meeting my expectations. 
I am not speaking in generalities here,,I am stanch dogmatic religious on that POV.
Now as for amps,, sure there are some tube amps, than  may lose in a  shootout with some ss amps, this is quite likely. 
But in general, a  well designed (that'll cost ya bud) tube amp will out perform  ss amps  costing 2X's+ more
THere is hype in both designs. But in general , you can find more snakeoil flowing through ss designs.