I'm sorry. I'm still unclear. If I turn the preheat off with the power switch pressed on, the light on the preheat still is glowing so it doesn't seem like the amp is off. Is it? I'd like to keep the amp on all the time as I do my other equipment because in my experience, things sound a lot better that way. With tube gear, it requires a separate switch for the tubes but I'm still unclear if the preheat switch is what that is for.