pauln said:
Can you explain how a tube watt is more powerful than a solid state watt?
As far as I can remember from doing an engineering degree, a watt is a unit of measurement of power, defined as strictly as a metre or a kilogram is.
Not all watts are the same. You may recall from your engineering degree that a watt is the product of the voltage and the current, which are easily measureable quantities like a metre or kilo. So a given quantity of watts could be very high current or very high voltage or something in between.
In the case of tube and class A amps, people often talk about their wattage as being somehow 'more' than a class AB amp of the same wattage. In this case it's not just about current and voltage, it's about useable watts. Most SS amps depend on having lots of power to sound good, since they sound the best when taxed the least (and as another poster said, they sound horrible when they clip). Thus high-end SS amps tend to have lots of watts, to provide headroom.
Tube/class A amps have a more linear distortion profile - they operate very consistently up to their power rating and thus handle transients better, so that their sound seems more soft and organic. So a good 20 watt tube amp probably sounds decent even when you are using all 20 watts, whereas many SS amps rated for 50 or 100 watts may only really sound their best putting out the 'first' 10-20 watts anyway - driving them harder with low impedence speakers, say, and really using those extra watts may result in music that sounds harsh and fatiguing.