In general, with other variables held steady, as the power rating goes up dramatically (10x), the perception of loudness only doubles. 3,000 Watts sounds only “four-times louder” than 30 Watts. It seems unlikely, but measurements and anecdotal evidence have consistently shown it is generally true.
People often ask, how does the Milbert BaM-235ab compare, in terms of sound quality and loudness, to a transistor amp? It’s a simple question that uncovers many complexities. One answer is it’s so subjective, because the character of amplification and overload sound different; therefore, it comes down to approximation and personal preference. Please keep in mind we are necessarily speaking in broad, general terms.
In general, tubes overload softer and don’t hard-clip like transistors overdriven – giving more ‘cushion’ and ‘headroom’ before distortion becomes objectionable. Also, the overdriven spectra of a tube amp sounds different: softer, more full, not as harsh. So, when pushed hard, transistor amp distortion generally sounds much nastier than tube amp distortion. Guitarists (who often seek “good sounding” distortion using tube amps) have solidly demonstrated this for many decades, which is why we make GAGA.
http://milbert.com/articles/tubes_vs_transistors_perception