How loud is a 150 W SS amp compared to a 30 W Tube amp?

Anybody who thinks 2% THD is a sonic jumble is one of those "golden-eared" audiophiles who thinks he can hear the difference in a power cord made of oxygen-free copper. Normal people can't hear it at all. 10% THD is noticeable, but was established as an industry standard from research done in the late '20s and early '30s that showed most people didn't find distortion objectionable for AM radio listening up to 10%. Anytime you can hear "crunch" in your electric guitar, you're getting a lot more distortion than that. The limit of amp harmonic distortion is the percentage of harmonics in a square wave, which the waveform approaches as it's clipped more and more. I haven't looked up the total percentage of harmonics in a square wave, but I'm sure Google would turn it up. (A square wave is made up of the fundamental frequency and all of its odd order harmonics.) Heavily distorted (overdriven) guitar comes pretty close to square waves, with the higher harmonic content being filtered by the amp's and speaker's frequency response curve. (Looks like rounding off the corners of the square waves when put on a scope.) Also, RMS power calculations from the peak voltage of a waveform only work for a pure sine wave. A square wave of the same peak voltage contains a lot more power. I'm too lazy to hunt up the formulae right now. But as the distortion level increases, the actual power of the distorted waveform is going to be quite a bit more than an undistorted pure sine wave of the same peak voltage (output voltage being what's limited as an amp is driven to saturation.) This is important because so many guitarists do drive tube amps WFO. (It also explains why so many speakers get fried that are rated for the amp's rated output power.)

Great info!

Thanks for the practical information!