Peavey Bias Mod

[RockGuitarX]

I've read a lot of reviews/forums where people talk about getting a bias mod for both the 5150/6505 and the 5150II/6505+ . What exactly is this mod? What does it do? AND Most importantly, how is it done? For example if I wanted to get it done locally by a guitar tech, what would I show or tell him what to do? Thanks!

 

[Torniojaws]

It adds the ability to adjust the bias on the amp more accurately than the very little you can do with the stock amp (I think it was 6505+ that has the small bias knob with very little range).

If you don't know, biasing basically means setting up the functional current of the tube pairs ("engine idle rpm"). Different tubes have different optimal settings, and whenever you change tubes, that current will change due to small differences in the tubes. Too high current burns up the tubes faster, too low current thins out the sound.

 

[RockGuitarX]

It adds the ability to adjust the bias on the amp more accurately than the very little you can do with the stock amp (I think it was 6505+ that has the small bias knob with very little range).

If you don't know, biasing basically means setting up the functional current of the tube pairs ("engine idle rpm"). Different tubes have different optimal settings, and whenever you change tubes, that current will change due to small differences in the tubes. Too high current burns up the tubes faster, too low current thins out the sound.

Thanks for the reply. I know what biasing is, I'm just confused on the bias mod details. As I mentioned earlier, what would I tell a guitar tech to do?

 

[Morgan138]

When I had this done on a V-4b I just told the tech to put in an adjustable bias pot, and he knew exactly what to do. It's a pretty common thing, and if they don't know what you're talking about right away I'd take the job somewhere else.

 

[RockGuitarX]

When I had this done on a V-4b I just told the tech to put in an adjustable bias pot, and he knew exactly what to do. It's a pretty common thing, and if they don't know what you're talking about right away I'd take the job somewhere else.

LOL good point.

 

[Metaltastic]

What's a V-4b?

 

[yarrick19]

RockGuitarX - check your PMs. I have a PDF document with some details on the bias mod that may help you out... I don't see a way to do attachments on this forum but I can email it to you if you are interested in it.

 

[everybody's x]

What's a V-4b?

a kick ass old ampeg head