A Guitar And Gear Support Forum

So, how hot should power tubes get?

I plopped new Mesa SPAX7s in my Classic 20. In the process, I noticed that my power EL84 power tubes were very hot: like if you lick your finger and touch them it sizzles hot.

Is this too hot? These aren't exactly new power tubes, so if I need new ones, no biggie.

I think they normally get that hot.
For safety, test them with your tongue.

One of the reasons I dislike EL84's. They all run that hot.

Ok, I will hold off on replacement then. Thanks!

Look at them with the lights off. If they are glowing red on the plates they are biased too hot. Chances are it's normal, output tubes run hot usually and will burn your fingers.

This is only written to be post #10,000 on the new AGF.

Mods, please delete the post above.

el84 push pull cathode bias amps are common designs. The cathode biasing is often at or even a little above %100 plate dissipation.
So yeah, they get HOT.

Great advice in prior posts. Looking at the schematic, this has 110 Ohm cathode bias (two 220 Ohm in parallel) - that is bias way hot, like a Vox AC30.

Glad nothing is wrong, because it is a magical little amp. I will never sell it, and if it dies...maybe a Classic 20 head with a 2x10 cab would happen.