Vacuum Tubes - Are they Warmer Sounding?

In a word: YES.Why? The phenomena is simple in theory but geplex to explain fully. I'll make an attempt here to do so. We are talking about the difference between vacuum tubes and solid-state devices, e.g. bipolar transistors and semiconductor IC's. Note that I did not include FET devices, which are a form of solid-state device but operate differently than the other solid state devices - I'll cover these later. The answer lies in the harmonic content that the device [tube/transistor] can pass or generate. What's known is that the human ear finds 'even' harmonics pleasing and 'odd' harmonics annoying or grating, or in the least unmusical. First a word about harmonics. Harmonics, for those who are not versed in wave theory, are simply frequencies which are related to the fundamental frequency being reproduced and are generated in sympathy to the fundamental note. As an example, a note on a piano or guitar string when struck contains a fundamental frequency plus other frequencies that are odd or even multiples of that fundamental note. This is a naturally occurring phenomena, and are often called overtones, and is what give an instrument its characteristic sound. It is important to note that these harmonics are predominately even. If no harmonics were present the note would be a pure sine wave and sound like a single tone.To illustrate, a 100Hz sound wave, if not pure, may generate harmonics out to the nth order. How strong and how many of these harmonics are present will determine the harmonic content, or harmonic distortion (THD) as it is characterized (when deemed undesirable). An example: a square wave has 100% harmonic distortion, the fundamental plus all its harmonics are present in equal amounts. In a square wave (e.g. digital) harmonics are very desirable. In fact the more the better. In the analog world and musically speaking, the inverse is true.What are even and odd harmonics? It just refers to their respective mathematical relationship to the fundamental. Using the same 100Hz example, the 2nd, 4th