tube watts vs transistor watts?

That is not correct, it depends on the amplifier. My Musical Fidelity NuVista M3 is rated 275 at 8 ohms, my tech friend measured 325 with extremely low distortion. It will pulse over 800 watts at 2 ohms. Any good amp will deliver much more than its rated power for very short bursts, that was the basis of the late , unlamented "peak" power or "music" power ratings. Any amp that behaves as you describe is a bad amp and should be avoided.

One thing that tube amplifiers/preamplifiers do so well that solid state amplifiers do not is reproduce those wonderful micro dynamics. Those subtle nuances. So when listening to tubes you are not looking so much at the big dynamics like drum beats etc but rather to the subtle musical characteristics and so you don't feel the need to turn up the volume as much, you hear more at lesser volume.

So perhaps not so much about power as about perception.

Sounds_real_audio, I agree with you. I think its more an issue of perceived power than what the speaker will handle. With tubes we tend to be satisfied with fewer watts instead of continuously increasing the volume to bring out something in the music we feel we are missing. Sure, you can get this in solid state electronics, but the price is much higher.

Stanwal, I went to the Stereophile website and randomly selected a solid-state amp reviewed there (since they have nice graphs in their review). Ok, not so randomly selected--it was at the top of the list and it's probably the most recently reviewed. :)

It's an Electrocompaniet AW400. Looks like a reasonably nice amp, $12,500 (pair of monoblocks). Look at the graph on Atkinson's measurement of power output, Figure 3. The curves do exactly what I said: slow decrease in THD with rising power, until suddenly they hit a barrier and spike drastically upwards.

You might say that SS amps have a dramatic change in the second derivative of their power vs. THD graphs right around their rated output, compared to tube amps. That very different approach to distortion results in the effects that we've been talking about.

So tube amps and SS amps are different beasts when it comes to power ratings, and it is quite valid to make a correction accordingly. A rule of thumb I've seen here and there is that N watts of tube amp is about the same as 3N watts of SS amp, because of this effect.

Now if you can make absolutely, positively certain that your SS amp will never distort as the signal level routinely approaches that boundary, then you can change that rule of thumb accordingly--but that's a toughie.