A solid state amp produces a signal voltage at the output. No current flows until a load is put on that output. You can run a solid state amp all day without a load, it won;t care. In fact we run them without a load here on the bench until we are certain they are not putting out DC.
Tube amps MUST have a load, all the time. It isn;t about length of time, you can turn up your tube amp without a speaker and destroy the output transformer with one strum of a chord. or you might get away with it for a long time, you never know. Many amps have flyback diodes across the output to protect the circuit from this. Unloaded output transformer can reflect the waveform back at seriously elevated voltage, which can puncture the insulation and arc the transformer windings.
SS amp power is generally fairly low voltage to start with, darn few we see with rails over 100v, and there is no transformer to kick back-voltages up with its inductance. Tube amps start with plate voltages in the 500v range, and the inductive kickback of the unloaded transformer can kick it up over a kV easily. Most flyback diodes are 2000-3000v.
Whump is limited to the power rail voltage. If your amp runs on +/-50v, then 50v is all the larger a peak can be. All by itself, whump sounds pretty dramatic, but it is no louder (and probably a good bit less loud) than the loudest passage the amp can pass. If the speakers can handle the full output of the amp, then the whump is not a problem. Bascially it is no different from a kick drum hit.
