what makes a tube sound the way it does?

There is no such thing as the right type of distortion.

Tubes do have much lower open loop THD than transistor i.e. tubes are more accurate.

+++ Solid state can be more robust and play at much higher levels with better linearity = more accurate +++

Patently false. A transistor will turn to smoke when overloaded (I have done that many times), while tube can withstand overloads with little ill effect (I have done that many times too). Tubes are extremely robust but transistors are extremely fragile.

Transistors are totally “un” linear and measure at up to 70% THD run in open loop. They normally require copious amounts of feedback to sound linear. Many vacuum tube amplifier can run with zero % negative feedback.

+++ A good linear tube amp will actually sound almost identical to solid state up until the point it clips (often this occurs at very modest levels due to transient peaks) at which point it gives that famous "tube sound".+++

Again, patently false. I never clip my tube amps and they sound like tube amps the whole time i.e. accurate, natural and real.

I have heard some nice sounding transistor amps, but they do not sound natural or real.

Regards
Paul

Tubes overload easily. Tubes sound nice in overload. They act like a compressor.

I gotta comment here: transistors and tubes overload equally easily. Neither has any particular dynamic range over the other. The rest of the above quote is true of tubes in mild overload and is something transistors do not do.

Tube amps are voltage driven which produce even harmonics,solid state is current driven which produces uneven harmonics.That pretty much sums it up,right.

OTL stands for output transformerless

No one talks about what I believe is an important factor in the difference between the sound of tubes and transistors. Tubes have a far superior dielectric, or lack thereof, because they have a near vacuum surrounding the conducting elements. The signal is not impeded or impinged upon by anything, not even air.

Transistors or semiconductors require the signal to pass through layers of solid materials (silicon, plastic, metal) which are far from ideal dielectrics. Just as a cable with a poor dielectric sounds closed-in and clogged, so do transistors when compared with vacuum tubes.