Dennis Fraker of Serious Stereo often comments on how music is pulsed and not entirely sinusoidal in composition.
The late Bernard Salabert of Phy-Ph loudspeakers commented that 70% of music is non-sinusoidal.
I examine the how fast the voltage at the output of the amp settles after a pulsed test tone in LTSpice.
Note : I am no LTSpice expert and the test results are probably generic but still interesting to observe.
If anyone has some additional information on pulse testing tube amplifiers, please contact me at my deathtube email address that is posted on this website.