EVH Brown Sound - Variacs and Tube Biasing

GreatGreen

GreatGreen

Power User
Conventional wisdom around the Brown Sound is that Eddie used a Variac to dial his Plexi down to 90v, after which he would then re-bias his EL-34's back up to normal ranges.

How does this work in the Axe-Fx III? If you decrease the Variac value, is it necessary to increase the Grid Bias value to get the tubes in the "correct" range again or is the Grid Bias control normalized so that it's always "correctly" biased no matter how the Variac control is set?
 
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The thing about bias in a real tube amp is that there isn't really a correct setting but there are suggested values. Tube manufacturers recommend biasing such that you're getting about 70% of the tube's rated plate dissipation. This is to strike a balance between a good level of output and tube longevity / reliability. Amp designers build their circuits with those values in mind, so that's always a good starting point. As the end user you can choose to bias your tube amp more conservatively than the 70% figure and get longer tube life or go hotter and get more output power with detrimental effects on tube longevity. The bias on the power tubes also has an impact on the tone / feel of the amp.

In the Axe-Fx the only impact is on the tone / feel since there are no reliability issues to consider. I don't know whether or not the variac control has any impact on the grid bias parameter in the Axe-Fx, but does that really matter? Why not simply adjust the parameter to where it sounds best for the tone you're after?
 
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OrganicZed said:
In the Axe-Fx the only impact is on the tone / feel since there are no reliability issues to consider. I don't know whether or not the variac control has any impact on the grid bias parameter in the Axe-Fx, but does that really matter? Why not simply adjust the parameter to where it sounds best for the tone you're after.
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I mean sure, I don't suppose it really matters in the grand scheme of things, and I agree that ultimately, one's ears should have the final say in dialing in any kind of sound for anything. But in the sense that it's fun to know as much as you reasonably can about the things you're into I think it would be fun and useful info to have.
 
FWIW - I've been using my 'ears" ....

When you dial back the Variac the volume drops ever so slightly .... Then when you dial up the Bias the volume goes up quite significantly ....

I just dial up the Bias until the volume comes back to approx. the pre-Variac volume ....

So, to my way of thinking a little Bias increase goes a lonnnnngggg way !
 
I've settled on a recipe of Variac @ 75% and Bias @ .75-.80. Sounds and feels really good. I'm not in front of the unit at the moment, so the bias scale may be different, but you get the idea. Works great with all the Plexi models.
 
And for those wanting to try IRL. I think the one you want is the Staco 3PN1010B. Or, the fancier 3PN1010BV : V for VU meter. That's what I ordered at least ;)
 
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