When an output tube blew in my Rogue Cronus Mag. II, a while back, I called Rogue to get advice and order a new set of KT-120s. Rick told me that I could expect to get about 2000 Hrs. from a set of the KT-120s and several thousand from the input tubes. Since I listen to my music for about 40 - 50 Hrs per week that would be a new set of tubes every year - even If I faithfully turn off at the end of every secession. Rick told me that there is no sonic advantage to a warm up of more than 10 or 15 minuets on that amp, so, in lieu of cost and headaches, I'm being a bit more mindful of shutting it down between listening sessions...Jim