Quote Originally Posted by skeptic

One amplifier I can report sounded harsh and bright was an early model made by a company called Acoustech which was later bought out by Koss. It had surprisingly high harmonic distortion for a solid state amplifier running about 1%.

Among vacuum tube amplifiers, even Marantz must have felt that there was a difference in sound because they provided a switch on the Model 8 power amp which allowed the user to switch from pentode to triode operation but with less maximum power (I think the reduction was from 60 watts for the pentode to 40 watts for the triode.

The heart and soul of any audio power amplifer regardless of its type is its power supply. You can often tell a lot about the quality of an amplifier just by how heavy and large it is.
I accept 1% THD as the liimit of audibility (at lower frequencies). An amp with 1% THD into 8 ohms @ 1 KHz probably can be distinguished by golden ears with test tones (don't bet on music). IMHO an amp with 1% THD is not performing properly.

People have demonstrated that they can distinguish tube amps (probably because of freqency response errors due to impediance mismatches). Tube amps are also not "performing properly" according to me (and are therefore excluded from consideration in the question of whether properly performing amps sound different). The fact that some people LIKE the improper performance of tube amps is okay by me, but not good evidence that they sound "better". Why pay extra for an amp with built-in non-adjustable tone control? Most tube amps are simply inferior for a host of reasons beyond sonic inaccuracy (such as the fact that they go out of "alignment" with alarming regularity).

I'm all for good build quality, and I somewhat agree that it coreleates to weight (though manufacturers often fool people by using a heavy case). A good design using proper integrated circuits could be fairly light weight (e.g., the Marantz monoblocks). The problem is; how much am I willing to pay for things that don't affect audible performance? Expected longer life is a crap shoot (I have a SS Yamaha power amp from the early 80s that works just fine). So, if you have the bucks for solid build and great measured performance, go for it--just don't pretend it "sounds better".

I appreciate skeptic even temper. Is he mellowing with age?