Question for the Audioholics community. I have an old Rotel RB-986 MkII 5-channel amplifier at the center of my home theater system. Lately it seems that we need to increase volume on shows and movies more than we did in the past. I'm wondering, do amplifiers have a "half-life" where their poser output declines over time? I've had the amp for 20+ years and wonder if it's time to retire it.