I know never to run a tube amp without proper impedance or a speaker load but how about solid state amps. What if any damage can be done by not properly loading them?

 

I think there is zero problem for most designs, but of course every design is different. I know for a fact that my Yamaha receiver doesn't care whether a speaker is connected or not.

 

Tube amps have output transformers which are driven by tubes that have a relatively high impedance output and thus look sort of like a current source. If you open the transformer secondary then the tubes will generate high signal voltages in response, since there output impedance is not loaded, which can arc over in the transformer windings and damage it.

Solid-state amp (almost always) have no signal transformers and have a low output impedance, looking simply like a voltage amplifier, so whether they have a load or not has little effect on the signal output voltage, and thus they are not damaged by no load.
The can however, be damaged by a short circuit on the output if they don't have a built-in protection circuit for that.

 

Tube amps have output transformers which are driven by tubes that have a relatively high impedance output and thus look sort of like a current source. If you open the transformer secondary then the tubes will generate high signal voltages in response, since there output impedance is not loaded, which can arc over in the transformer windings and damage it.

Solid-state amp (almost always) have no signal transformers and have a low output impedance, looking simply like a voltage amplifier, so whether they have a load or not has little effect on the signal output voltage, and thus they are not damaged by no load.
The can however, be damaged by a short circuit on the output if they don't have a built-in protection circuit for that.

I should have added that I recently bought a 25w stereo amp with a tube pre amp and solid state power section. So should I be careful of having speakers connected always?