The only thing that's going to be hurt by leaving a tube amp on all day is your electric bill.Wait... Are you guys saying it's ok to leave the tube amp on all day? I mean, I grew up with tube TVs and they were on for most of the day almost every day but I have been conditioned to think that "your precious guitar tube amp should be off when you are not using it, and make sure to not turn it on/off more than 3 times a day". Is that not correct?