# Peavey Butcher Bias Mod and Test Points



## Josh Lawson (Sep 11, 2008)

Most PV amps are bias very cold. The Butcher is almost an exception, the Power tubes run at 26Ma. This is not quite right when you do the math. 30W divided by 485V = 61.8Ma max dissipation. Multiply this bu 70% and you get 43.3Ma. So my friend and I installed a 1k variable bias in R52 (see the schematics posted below). 

http://www.schematicheaven.com/newamps/peavey_butcher.pdf

Here are some Pics of the mods.





I love how the bias pot and test points are right in the middle of the shock warning!! 




This reading is a cumulative Ma rating of all 4 power tubes. Originally, this amp's Ma was down around 110. 

The tone is vastly improved and the testing is easier to do than running a bias probe. My buddy who helped me has a more detailed account of the procedure here:

Half Nrrdy, Half Music, Half Absurd - Always poor at Math » Article » The Peavey Butcher

Thanks for checking this out and keep on rockin'!!


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## dpm (Sep 11, 2008)

Cool!


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## Josh Lawson (Sep 11, 2008)

The test point were really difficult to figure out, but the Bias pot was really easy. All that was required was a quick desoldering of one resistor, drilling a hole in the chassis for the pot to sit in, and soldering two wires to the holes that the resistor sat in. We chose the secondary voltage divider (R52)rather than the main bias resistor (R53) because of the smaller resistor Ohm value (more safe and precise adjustment), 470 ohm vs. 47k Ohm, respectively. I'd like to thank my friend Patrick Fitzgerald and all the grood folks over at the AX84 forums. Build your own amp guys are really helpful!!


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## Ishan (Sep 12, 2008)

That's a very cool simple mod. I've never seen one of these amp over here, were they only sold in the US?


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## Josh Lawson (Sep 12, 2008)

Ishan said:


> That's a very cool simple mod. I've never seen one of these amp over here, were they only sold in the US?


Yes. They where only made for 2 years('84-'86). The tone of this amp is similar to JCM800/Laney AOR. They are a single channel amp with mid gain. I run just about any dist. pedal into the low gain input and the tone is now amazing. The one striking feature about this amp is it's incredible weight, about 75 pounds for just the head. The tone is worth it though.


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## Ishan (Sep 12, 2008)

Ever tried to push it with an OD?


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## Josh Lawson (Sep 12, 2008)

Ishan said:


> Ever tried to push it with an OD?


 Yes. and it sounds very good like this to, but if I run it like this, I have no clean tone. These amps have a better clean tone than a 5150, and take to dist pedals better as well, IMO.


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## Ishan (Sep 12, 2008)

Good point


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## HamBungler (Sep 12, 2008)

Josh Lawson said:


> Yes. and it sounds very good like this to, but if I run it like this, I have no clean tone. These amps have a better clean tone than a 5150, and take to dist pedals better as well, IMO.



I find with a good OD you can still retain clean tone, heck my Nobles ODR-1 ov Chaos is pretty darn transparent if you run the drive low or turn the guitar volume down a tad, actually makes my clean sound better!  Just a thought though, whatever works for you bro.

Good work on the mod as well!


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## Josh Lawson (Sep 13, 2008)

Right now I'm running a Dean Markley Overlord into the high gain channel, setting both gains (pedal and amp) at about 7. This absolutely nails early 70s Sabbath. I am playing a Sabbath tribute night on Halloween so for now, this is what I am going for!


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