EL84's glowing brighter when playing notes hard

[rhaigh]

When cranking my Peavey Bravo, the tubes(2 el84s) glow a brighter orange when I play a hard chord or low note. It's not red on the plates, it just flashes orange brighter when I play. I have it adjusted to 20mA idle current -- 12(0.7)W/411Vp. Is this normal when playing at full power? Should a bias it a bit colder if i'm going to be playing a full power sometimes? Thanks.

[Enzo]

Don't over think it. Just adjust the bias as you would, and enjoy playing the amp.

[rhaigh]

It's just that I don't want it to red plate. When banging on a bassy low E for a while, it stays a constant very bright orange. Much brighter than idle or when I play higher notes when doing high lead solo stuff. It red plated once before awhile ago, but the bias looked fine so I figured it was a bad tube, so I changed the tubes and its been fine ever since. The reason I noticed the bright flashing tonight was because the sound started getting a bit weak and crappy while playing , so I had a look at the tubes. I rechecked the bias afterwards, it was fine, so I played again and it sounded fine, even with the flashing. I never noticed it with my EL34 amps, but I 'spose I don't play those at full volume very often.

[Enzo]

But you said it wasn't red plating. Under high power, the screen grids can glow, this is easily seen in EL34s because of the little windows in the plate structure. Glowing screen grids can be visible as interior lighting.

[Chuck H]

Yu may have a loose solder connection, bad trace or a dirty tube socket. Any orange glow from the tube should be coming from the filament only. The filament shouldn't fluctuate with plate current (though I've seen it happen for unexplainable reasons, to me anyway). If you're seeing orange glow other than the filament then you may be over dissipating your plates or screens. Since you checked the bias and it looks right I can only speculate that the higher vibration of heavy playing, especially bass notes, may be triggering an intermittent bias fault. I would suggest checking solder connections on the power tube pins and their associated board connections and cleaning socket contacts for starters.

[Enzo]

Te cathode is nearly white hot, and as current through it increases, so can its brightness. The screens are visible in larger tubes, I would assume in EL84s they act similarly. Glow from within the plate structure can shine out the mica end plates.

[mozz]

When you say you are measuring the bias, are you doing it correctly by measuring the plate voltage also and figuring out the dissipation? A lot of el84 tube amps really push those tubes past the limit and they have a short life, maybe they are toast again.