Playing thru my usually reliable Matchless Dc-30 tonite , and noticed the sound was unusually brite and harsh. Like a hard, SS breakup. No snap as usual. I haven't played this amp lately and have been favoring a couple of others, but I certainly didn't like the sound I was getting on any of the channels. Would you say, Powertubes, pre-amp tubes, both or something else would be the cuplrit. Hard to describe as it was plenty loud, but just cutting and stiff. Nothing like it used to be. Suggestions?