Tube Amps--Is Design the Primary Source of 2nd Order Harmonics?

[Steady339]

Tube amps--is amplifier design the primary source of those good sounding even order harmonics audiophiles love, or are tubes--especially NOS tubes-- the primary source of even order harmonics?

[Rayooo]

many many moons ago, when I went to school, I learned on tubes strange thing was, when I got out of school, I never saw another tube in the real world.
..by real world I'm speaking of anything other than audiophileville.

Hopefully some of this is correct and makes sense:

In single-ended tube designs, with plate resistors and little or no feedback, conduction in the tube itself causes slight variations in the plate voltage on positive and negative portions of the AC input. this variation, when you graph it out, looks just it would if you added a bit of 2nd harmonic into the fundamental. The harder the tube is driven, the worse (or better if you like 2nd harmonic distortion) it gets... eventually this becomes "soft clipping" which if you play guitar, ya just love.

Feedback, push-pull designs, grounded grid, etc.etc. can minimize the effect, thus these topologies could tend to sound less tube like.

So I guess the answer is yes, the basic way a tube works, when used in specific designs, can have more, or less, 2nd harmonic distortion. As the designer, you get to pick how much.

No doubt, specific characteristics of individual tube types affect this as well.

Lots lots more than this to it, I forgot more than I ever knew about tube circuit design... and I never knew much to begin with.