Here is the opinion of a High End retailer, "The Tweak Shop." It's only one opinion, take it for what it's worth.
http://www.tweakshop.com/Tube%20care.html
"Should I Leave My Tubed Component On All The Time?
"In 95% of the cases, no. There are a few components out there (like the T+A V-10 Integrated Amp) that have special circuits that provide a "trickle" voltage to the tubes, even when the component is turned "off". This does two things: It prevents the tubes from being "slammed" into operation when the unit is on, and it also means your "warmup time" to optimum listening is considerably reduced. Components like this are, therefore, "on" even when not "turned on", but this is a rarity. Energy-wise, a constant "trckle" voltage is not something we can recommend, as it can add up to a massive waste of resources. (Fortunately, that feature of the T+A V-10 can be switched in and out.)
"In an ideal world, we'd all use massive Vari-Acs to slowly bring our tube equipment up to operating voltage. But that's an impractical fantasy.
"It's something of a trade-off. Tubes don't like being turned on and off, but they also don't like being left on all the time just cooking. So it's sort of "six of one/ half dozen of the other". We think the tubes will last longer if *not* left on continuously, and many components feature a "soft-start" circuit that helps lessen the shock of turn-on.
"Bottom line: Unless you really do listen to your system 18 hours a day, turn off your tube gear and prolong the life of your tubes (and save big on your energy bill!)."
TOM AGAIN - And here is a link to a fairly lengthy discussion courtesy of someone who owns a recording studio, Sears Sound, on the topic of leaving equipment on or off. He does include vacuum tubes in his discussion.
He concludes that recording studio equipment should be turned off at night and acknowledges that others will disagree.
http://searsound.com/pdf/leaveiton.pdf
Again, it's not a scientific study, so take it for what it's worth and enjoy your music whether you leave your tubes on or turn them off!
http://www.tweakshop.com/Tube%20care.html
"Should I Leave My Tubed Component On All The Time?
"In 95% of the cases, no. There are a few components out there (like the T+A V-10 Integrated Amp) that have special circuits that provide a "trickle" voltage to the tubes, even when the component is turned "off". This does two things: It prevents the tubes from being "slammed" into operation when the unit is on, and it also means your "warmup time" to optimum listening is considerably reduced. Components like this are, therefore, "on" even when not "turned on", but this is a rarity. Energy-wise, a constant "trckle" voltage is not something we can recommend, as it can add up to a massive waste of resources. (Fortunately, that feature of the T+A V-10 can be switched in and out.)
"In an ideal world, we'd all use massive Vari-Acs to slowly bring our tube equipment up to operating voltage. But that's an impractical fantasy.
"It's something of a trade-off. Tubes don't like being turned on and off, but they also don't like being left on all the time just cooking. So it's sort of "six of one/ half dozen of the other". We think the tubes will last longer if *not* left on continuously, and many components feature a "soft-start" circuit that helps lessen the shock of turn-on.
"Bottom line: Unless you really do listen to your system 18 hours a day, turn off your tube gear and prolong the life of your tubes (and save big on your energy bill!)."
TOM AGAIN - And here is a link to a fairly lengthy discussion courtesy of someone who owns a recording studio, Sears Sound, on the topic of leaving equipment on or off. He does include vacuum tubes in his discussion.
He concludes that recording studio equipment should be turned off at night and acknowledges that others will disagree.
http://searsound.com/pdf/leaveiton.pdf
Again, it's not a scientific study, so take it for what it's worth and enjoy your music whether you leave your tubes on or turn them off!