Dharm, in my view tube amps represent an obsolescent technology and there's no good reason to seriously consider them. The distinguishing factor affecting most tube amps is a much higher output impedance(an ohm or more)compared to solid state amps(less than 0.1 ohms typically). This can result in the output "following" the swings in impedance of the speaker being used and therefore deviating from flat frequency response. For example, where a speaker has one or two large impedance peaks in the bass area, the tube amp would have a slightly elevated response at those points, which could be interpreted as "warmth", although in fact it's an inaccuracy. There's also a difference in the distortion characteristics of single-ended tube amps that make the onset of distortion less objectionable than in push-pull amps, but it's still distortion. Where the impedance or distortion effects don't create significant differences, the sound is identical.
