tube watts vs solid state watts

Loudness relates to Gain (Volts out per volt in), not to power rating which is simply the maximum that can be output without unacceptable distortion. A low power amp, perhaps a tube amp, with a high gain will play louder, for a given setting of the volume control, than a much more powerful amp with lower gain so long as the maximum power of the smaller amp is not exceeded.

A watt is voltage times current, regardless of whether the juice is generated by a tube amp, a solid state amp, a magnetic amp, or any other type you can think of.

People go on and on about one brand of tube vs another, but I think that it is the audio output transformer which largely determines the sonic quality of a tube amp. It's not easy to "roll" transformers so there is little discussion of this subject.

The early success of Dyna Kit (later known as Dynaco) was due to the fact that before they designed and sold amplifier kits they were a manufacturer of top notch transformers.

The clipping characteristics of tube and ss amps do differ, and tubes do sound less harsh and do less harm to tweeters. However, except in Pro sound applications, anyone who, on a regular basis, drives their amps into clipping is simply using the wrong amp. Solid state amps can have circuitry that detects when clipping is on the verge of happening, and prevents it by a gain reduction. Of course this is compression, but at extreme volume level it is scarcely noticeable, and sure is better than clipping. Pro sound amps are most likely to have this feature, because these amps are often used right up to their power ratings, and with live sources that can not be preauditioned to set gain. I am using CarverPro digital amps, 600 wpc at 4 ohms, that have clip detection, and I have this feature switched on. Much to my surprise I discovered that my Maggie 1.6 speakers, 4 ohms, can trip the clip limiter feature if I play certain music at too high a volume level.