The classic topic, tubes vs. solid state. /lol/
Tube Amp Distortion.
Tube amplifier amplifying a 1khz sine wave.
Clean signal just like a solid state amp.
Tube amplifier over driven into high distortion.
Look at the shape of the sine wave, it's mangled.
Solid state amplifier clipping
The more you over drive the sold state amp the more it starts to look like a square wave.
Here's another where the tube amp is operating cleanly and as you over drive the tube amp,
the sine wave becomes mangled and eventually looks like a square wave if you over drive it enough.