This thread has been discussed many times. There are several ways to go here. First, basic engineering will tell you that unless it is absolutely necessary, you never leave this type of equipment on all the time. Components will defintely wear out much quicker with heat and time on. Manufactures will install fans only if it is cost effective for them to do so. Each piece of equipment is designed and constructed and sold at a particular price point in competition with other components at that same price point, much the same as computers and cars/trucks. A Mercedes SL600 is most definitely not the same as a Toyota. The same holds true for high end audio equipment. Also, unless the manufacturer is a goverment contractor for military usage, they will not perform failure test on equipment. Again, it is not cost effective. They won't test to determine the failure rate or how long leaving equipment on will take it to fail. It just won't happen. Some may adjust bias or add fans or elaborate heat sinking to dissapate the heat if necessary. Again, building to a price point and some of this may not be cost effective with the competition. If you want to leave your equipment on all the time, talk with the manufacturer and go for it. However, it is not necessary. Depending on your listening style. you can turn your equipment on an hour or so before hand and you would be good to go. But, to each their own.
If sound quality is important to you during playback, then try an experiment. Pick some music. Turn the equipment on two hours before hand and listen. take notes. Next day, turn it on one hour before hand and listen. Take notes. and then leave it on for an entire day, then come back and listen, take notes. Compare notes. I would be very interested to hear the discussion on the differences.
Also, it would be extremely unwise to leave tube equipment on all the time. Tubes have a very finite life span and you will wear out your tubes very quickly if they were left on. Very expensive endevour.
Enjoy
