Think of it this way, one of these days you'll have to retube the thing. Might as well get a set of new tubes now and try them out. If you hear a difference, well, then it was time. If you hear no difference at all, then put the old ones back in and rest assured that your time will come.
How does sound change when tubes start to fail?
Maybe a silly question, but I'm wondering how I can tell when the output tubes in my Fisher 400 reciever start to die? When I had it refurbished the techs told me the 7868 tubes were nearing the end of their usable life. I feel like the top end is less detailed and dynamic than it had been in the past , HOWEVER, I just moved and have a new listening room with less than optimal speaker placement. Thanks