"... 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