Warming-Up Amps w/o Inputs or Speakers Attached

I don't know about all of the solid state amplifiers out there, but I do know VTL and it is not recommended with your amps.

Don't do it with tube amps.

I have purchased 100 watt 8ohm dummy loads from Parts Express just for this purpose. Pretty cost effective at $13.50 a pair. They work great and they genereate no sound although they can generate some heat. Easy to keep those tube amps warmed up without any speakers or damage. Check it out at: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=019-020

Although it is unlikely, it is possible to damage a tube amp with no load connected if you play a signal through them. The transformers act like big inductors without a load, storing up energy and releasing it, and since the only place for it to go is back into the output tubes it is possible to damage the tubes this way. With a solid state amp it isn't a concern.

If you're not going to put a signal to them it is highly unlikely any damage would be done, but the dummy load idea is a good one just to be safe. Radio Shack sells cheap resistors you can use. Solder some banana plugs to them to make them easy to use.

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Transformers CAN'T, "store" anything, or feed anything back into the amp. Neither SS, not tube amps will suffer, IF THERE IS NO INPUT SIGNAL. I've turned on, and tested amp circuits, voltages, etc., with no speakers/loads attached to the outputs, for decades, with no damage. BUT- ANY input signal(even touching the inputs with your finger), on a SS amp, can be disastrous. The output devices MUST have a load to dump current into, or most will overload/fry. On a tube amp with an output transformer; the x-former acts as the load that the tube, "sees." Less chance for any damage to the tubes, or amp, without speakers attached. If you are worried; you can connect a pair of DUMMY LOAD RESISTORS, such as Mr M suggested, or these(http://www.mouser.com/ProductDetail/Ohmite/C300K10R/?qs=sGAEpiMZZMtbXrIkmrvidP2I4HgSKt85zTh%2fvGSbGfI%3d)across your outputs. Anything smaller(you won't find anything big enough at Rat Shack), and you stand a chance of damaging an amp, should an accidental input occur.