tube watts vs transistor watts?

09-23-10: Unsound
Tvad, it's possible for a given speaker to have both a low nominal and minimum impedance.

Isn't that the same thing as a flat impedance curve?

If that's not your meaning, then please provide an example of a low nominal impedance and a low minimum impedance so I understand your statement more clearly.

TVAD, it is :-). My speakers are spec-ed at: 4 Ohms nominal, 4 Ohms minimum. Many, if not most tube amps have 4 Ohm taps. In such a case, if one was willing to provide double the 8 Ohm tube Watts as a similarly rated 8 Ohm "double down" ss amp, all should be equal. If the speaker impedance load was 16 Ohms, the opposite would be true. Of course, I'm sure you knew that, but, it does clarify things for the OP.

Musicnoise
If I half the voltage that would double the current to get the same watts. If a speaker works better with higher current then it would be beneficial. Not all speaker will benefit from high current though. That's what I am trying to say.

Even a solid state amp that claims 200 watts of power does not make it a certainty that if impedance drops below 4 ohms and closer to 3 will it do the job without current. High, stable current with lots of reserve at the ready. Without it watts mean little in either camp. IMHO.
Cheers

There's lots of informative answers here but I'm not sure they have answered the original question.

When an SS amp approaches its power rating, it will go into distortion very, very quickly. Suppose it is rated at 200 watts; then if you try to get 210 watts out of it, you could easily get 10% THD or more. It will sound totally horrible. So in practice, you would not actually want to go anywhere near 200 watts with such an amp, because the power level of a music signal varies greatly and you are just asking for trouble.

On the other hand, the tube amp rated at those same 200 watts (this would be a little beast btw) can go to 210 watts and the THD might not go a whole lot higher than 1%.

So it's not so much that the tube amp is more powerful than its rating, but rather that the SS amp is not as powerful as its rating (by comparison); that's how I think of it.

That, and the realization that 30 watts is a whole lot louder than we think. :)