"tube watts" versus "solid state watts"

Actually...a watt is current times voltage. It is unlikely that an amplifier will "run out" of voltage capability at the same time that it runs out of current capability. You could have an amplifier with low "rail" voltages that could deliver huge amperage at a low output voltage. This would, of course, be a waste because the amperage actually drawn is determined by the voltage and the impedance of the speaker. Similarly an amp might swing a high voltage into a light load, or for a brief time, but be limited in steady state performance by current delivery capability. Still, there are enough technical grounds to support an audiophile argument that a "tube watt" is better than a "SS watt". It doesn't take much technical ground to support an audiophile argument :-)

2-left: this current thread (nopunintended) has some pretty good explanations and resources:http://forum.audiogon.com/cgi-bin/fr.pl?htech&1235758642&openmine&zzNsgarch&4&5#Nsgarch

A Watt is a Watt.
Beyond that my hyper technical response is . The measure of an amp of either tube or SS is how much it weighs. The question of where the watt is generated lies somewhere in the transformers . This is of great importance to the success of a tube Amp not the wattage. Indeed the better SS Amp has an enormous power trannie. In fact they weigh a lot if you aren't speaking of those wimpy on/off Chip amps. I will hold my opinions about the chip amp to myself.
So when looking for an amp first decide if you prefer a tube or SS amp by listening to both and ignore all this nonsense about the difficult nature of tube amps, it is pure B.S. Then buy the heaviest one you can afford, and please forget the watts.

Thought I'd expand a bit on my previous response. An example of how amplifiers are rated (which is done in accordance with requirements that are imposed, I believe, by the Federal Trade Commission), is as follows:

100 watts/channel continuous rms power at 8 ohms, from 20Hz to 20kHz at less than 0.5% THD (total harmonic distortion).

There are many reasons why two amplifiers that are identically rated in this manner at "100 watts" may differ significantly in real world power delivery.

First, for brief musical peaks an amplifier will be able to deliver significantly more power than its "continuous power" rating, the difference being referred to as dynamic headroom. The amount of headroom depends on many factors in the design, such as the amount of energy storage in its power supply.

An amplifier will have a clipping point, at which its output voltage cannot swing any further without a large increase in distortion. As I alluded to in my previous post, it is pretty well recognized that the onset of clipping for a tube amplifier is more gradual (less abrupt) than in the case of a solid state amplifier. That means, everything else being equal, that a tube amplifier will be able to exceed its supposed power rating by a greater amount than a solid state amplifier, FOR EQUAL LEVELS OF DISTORTION. A watt is a watt, but a "100W" tube amplifier will be able, at least on short term peaks, to be able to put out more clean, listenable watts than a solid state amp, everything else being equal. Power needs to be specified in the context of distortion to be meaningful.

There are many other factors than can make one "100W" amplifier more or less powerful (both subjectively and objectively) than another "100W" amplifier, some of which have been alluded to above, but which do not directly relate to the tube vs. solid state question. Different designers will provide differing amounts of margin in their power ratings, to allow for component tolerances, variations with line voltage, temperature, etc. As has been noted, amplifiers with similar power ratings into 8 ohms will differ in how much current they can deliver into low impedance speaker loads, or loads which dip down to low impedance levels at certain frequencies, and how well they can handle reactive loads, back emf, damping factor, etc.

Regards,
-- Al

I agree 1000% with Almarg; I'm no engineer but I'm quite sure that the main difference is that tube amps clip more softly and gradually than solid state. It's not so much a question of what different amps do when they're playing within their power range, but rather how they sound when pushed beyond it.