I haven't had too many EL84 amps. Lately when I start playing I really like my tones. I'm finding after about 30 minutes at band volume, my amp is starting to sound more fizzy/buzzy to my ears. Now that last part might be key....to my ears. One thing I haven't ruled out is that my ears might be perceiving the sound differently after playing at higher volumes. The other option is the tubes might be either getting old (bought the amp used) or maybe EL84s just get that way when they get hot. Just wanted a few opinions before I buy replacement tubes. I asked a couple of the guys I was playing with and they thought it was ok, but I could notice a pretty decent difference. Also I am breaking in a new G12H30. Could that be a cause?