Watts are Watts period. The SOUND is what most vendors refer to. Normally tube amps have more distortion but distortion is in even ordered harmonics, which sounds more pleasant. SS has odd ordered harmonics, which tends to sound harsher. For some of us the tube can be played louder with less listener fatigue because of this.
SS amps usually have more HEADROOM for transient music demands, tube amps with low power have less headroom so overall demands cannot usually be met at a equal higher volume level for a low efficient speaker if comparing SS to Tubes. This is why we prefer efficient speakers and speakers with less electronics in the way. Efficient speakers do not require a lot of current to produce signals at the max sound output, which usually is somewhere between 100-107db. This way a 8 watt amp can put the same Decibels out as a 400 watt amp, as the speaker just cannot go beyond this without physical damage.
The tube amp is usually the least expensive part of the overall equation as higher efficiency speakers can be very expensive compared to a lower efficiency counterpart.
SS amps usually have more HEADROOM for transient music demands, tube amps with low power have less headroom so overall demands cannot usually be met at a equal higher volume level for a low efficient speaker if comparing SS to Tubes. This is why we prefer efficient speakers and speakers with less electronics in the way. Efficient speakers do not require a lot of current to produce signals at the max sound output, which usually is somewhere between 100-107db. This way a 8 watt amp can put the same Decibels out as a 400 watt amp, as the speaker just cannot go beyond this without physical damage.
The tube amp is usually the least expensive part of the overall equation as higher efficiency speakers can be very expensive compared to a lower efficiency counterpart.