I recall from the reviews in TAS and Stereophile that ARC felt if you left the unit on all the time it would sound best, but you'd need to replace the tubes every 9 months or so. It's possible using better quality tubes might extend that life. Tough to tell when they're gone, because the sound deteriorates gradually so you don't notice the difference as readily, but in my case my system started to sound a little lifeless, lacking dynamic punch and clarity. There will definitely be more noise as well as the tubes start to go. And watch out for pops and sputtering!