is it ok to leave a tube amp on without speakers connected


I'm blessed to have two amps but one set of speakers in my listing room - all tubes.  Instead of cutting off one to listen to the other, I would like to listen to the other without powering off the one i'm not listening to.  

Question:  Can tube amps be powered on without speakers connected for hours at a time?
mudbone
What does the manual/manufacturer suggest or warn against or not. It's a yes and no answer. My Cary Rocket 88R  does not need to see a load and will not damage the amp by design.  Others will require a load to be safely used and not damage the output trannies.  Never follow the advice of anyone other than the manufacturer of YOUR product .
With tube amps the answer is NO!.you  will fry the output xfmr. SS amps may  be left on though however connecting and unconneti g spkr cables leaves you vulnerable to accidentally shorting the leads.

NO. NO NO NO NO NO. Had a pari of VTLs without my WATTS attached. Scared the color off me (I'm Hershey Brown colored). 

NO!!!!