# Peavey 6505+ bias adjust



## Winspear (Nov 1, 2009)

Hey guys - I have a 6505+ and read that biasing hotter will improve the sound of this head. I don't intend on getting the resistor or what it was changed at the moment, but I am aware of the bias adjust pot already present on this head. 
I heard it's not got a very wide range and can safely be turned up all the way, thought it wont make an incredible difference because of it's range.
I just took the back grille off, the dial was currently at 4oclock and can turn anticlockwise to 2oclock. I presume 4oclock is the coldest setting? Seen as thats how it was when I bought it. Just want to confirm that it's safe to turn this thing all the way around. 
Thanks.


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## st2012 (Nov 1, 2009)

It's safe. I actually asked this same question last month when I bought my 6505+. Turn the dial counter-clockwise all the way to warm it up.


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## Winspear (Nov 1, 2009)

Thanks


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## The Echthros (Nov 2, 2009)

did you guys really see a difference with the adjustment?


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## Leuchty (Nov 2, 2009)

il_echthros_777 said:


> did you guys really see a difference with the adjustment?


 
I noticed it when the dial was at opposite ends.

all the down = shit tone

all the way up = good tone


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## Andii (Nov 2, 2009)

I've got to try this. I'm satisfied with how it sounds now, so I might be thrilled to hear what happens.

Could anyone describe what sonic changes happen when the bias is turned up?


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## Leuchty (Nov 2, 2009)

Andii said:


> I've got to try this. I'm satisfied with how it sounds now, so I might be thrilled to hear what happens.
> 
> Could anyone describe what sonic changes happen when the bias is turned up?


 
tighter, warmer...useable. It may have a lot to do with the tubes you're running too.


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## Winspear (Nov 2, 2009)

CYBERSYN said:


> I noticed it when the dial was at opposite ends.
> 
> all the down = shit tone
> 
> all the way up = good tone


 
I wouldn't say it was that extreme at all, without the bias mod.
I was very happy with the original tone and I can hear a SLIGHT improvement with this pot turned up..but yeah, only at opposite ends I can hear a slight difference. But hey improvement is improvement. I'll look into the proper mod later. 



Andii said:


> I've got to try this. I'm satisfied with how it sounds now, so I might be thrilled to hear what happens.


 
Go ahead, might be more drastic than mine was, who knows. But don't get your hopes up that it will be a huge difference.


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## Andii (Nov 2, 2009)

EtherealEntity said:


> Go ahead, might be more drastic than mine was, who knows. But don't get your hopes up that it will be a huge difference.


After reading about it on different forums I'm not even going to try it. It offers change, but not usually improvement, sometimes even a negative effect. It looks as though where they set it is where the amp runs best.


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## kazE (Nov 2, 2009)

Andii said:


> After reading about it on different forums I'm not even going to try it. It offers change, but not usually improvement, sometimes even a negative effect. It looks as though where they set it is where the amp runs best.



The factory bias is very cold, nearly everyone who's had a real bias mod has loved it.


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## RideFour15 (Nov 2, 2009)

Is this the same bias mod that everyone makes a huge deal about and, typically, pay someone to do?


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## agoz20 (Nov 2, 2009)

Yes. This is the mod everyone makes a big deal about


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## Andii (Nov 2, 2009)

I don't get calling it a "mod". You turn a pot with a screwdriver.

EDIT: I must learn to read.


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## Winspear (Nov 2, 2009)

Andii said:


> I don't get calling it a "mod". You turn a pot with a screwdriver.


 
These are two different things, like I stated in my first post, I am not performing the mod yet.

The pot from the factory has a very small range. I.e. you turn it from VERY cold to FAIRLY COLD.

The MOD, changes a resistor, I believe, so the pot has a larger range. Turning from VERY cold to HOT and sounding a lot better (or so I hear).

Turning the stock pot as I was talking about gives a bairly audible improvement.


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## RideFour15 (Nov 2, 2009)

That makes sense; the job is actually swapping out a component and not just turning a knob.

Where did you find a schematic to find the bias adjusting pot?


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## Andii (Nov 2, 2009)

EtherealEntity said:


> These are two different things, like I stated in my first post, I am not performing the mod yet.
> 
> The pot from the factory has a very small range. I.e. you turn it from VERY cold to FAIRLY COLD.
> 
> ...



Ah I see. I apologise for not reading more carefully.  

I'm still interested in hearing everyone's impressions of the changes that occur with the mod and adjusting the stock range.


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## thadood (Nov 2, 2009)

With the 5150 II/6505+, replacing the 15k resistor for a 5-6k one will give you more headroom, dropping the then-super-cold side of the pot to be kinda warm to the then-kinda-chilly side of the pot to be warm to hot. So, when you do this mod, put the pot back to where it was.

I haven't done this mod on a 6505+ yet, but after examining a friends 6505+, the resistor is on a small circuit board (my memory is dusty, but I think it's the same board that the pot is connected to).


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## Leuchty (Nov 2, 2009)

EUROTUBES has a detailed explaination.


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