Watts are watts. Period.

Power = E * I
Power = I^2 * R
Power = E^2 / R

There’s no variable in there for tubes or transistors.

Now, that all said, there’s a big difference between how tubes and transistors behave when they get to the point of saturation.

When a transistor becomes saturated (fully turned on), it clips the signal…literally chopping the top and bottom off of the waveform. This is a type of distortion that humans perceive as unpleasant, so we turn it down at that point.

Tubes, on the other hand, do not have that “brick wall” they run in to. As they start to get saturated, they start to compress the signal instead of clipping it. Compression (and limiting) are audio processes that are used during the mastering of CDs, and by radio stations to make their sound louder. By compressing a signal, you lower the peak-to-average ratio. In simpler terms, the sound becomes more dense, and the psychoacoustic effect is that we perceive that as a louder signal.

So, as I said before, watts are watts. When you’re trying to figure out how much your speakers need to be able to handle, it really doesn’t matter what kind of amp you are using.

Greetings from Austin, Tx

Ken