5150 Combo Bias Mod
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  1. #1
    Little Dreamer

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    Default 5150 Combo Bias Mod

    Does anyone know where I can get technical info on the bias mod for the 5150 Combo? I found a good article on the head but the head and the combo are laid out very differently internally. I am specifically looking for the final resistor in the bias stage and I am having difficulty in ID ing the particular resistor.

    Help!!!

  2. #2
    Sinner's Swing!
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    I forget the guys name, but the guy at JJ tubes knows everything about the 5150 series as they engineered those tubes specifically for the 5150 to warm the amp up and take away the nasaly honk from the combo-and it works! Just Google JJ tubes or 5150 combo JJ mod and the guy and his website will come up. Call him, he is nice as hell and knows his shit! Good luck.

  3. #3
    5150
    A&Z Guitar Repair's Avatar
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    Quote Originally Posted by smme5150 View Post
    I forget the guys name, but the guy at JJ tubes knows everything about the 5150 series as they engineered those tubes specifically for the 5150 to warm the amp up and take away the nasaly honk from the combo-and it works! Just Google JJ tubes or 5150 combo JJ mod and the guy and his website will come up. Call him, he is nice as hell and knows his shit! Good luck.

    I'm assuming you mean Bob at www.eurotubes.com ?
    Scott Eivins
    A&Z Guitar Repair

  4. #4
    Little Dreamer

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    Default

    Quote Originally Posted by smme5150 View Post
    I forget the guys name, but the guy at JJ tubes knows everything about the 5150 series as they engineered those tubes specifically for the 5150 to warm the amp up and take away the nasaly honk from the combo-and it works! Just Google JJ tubes or 5150 combo JJ mod and the guy and his website will come up. Call him, he is nice as hell and knows his shit! Good luck.
    Hey thanks I will check this out. I replied to a posting from Dave King regarding a schematic for the combo. I have the one for the head and he's right it is quite different. Thanks

  5. #5
    Little Dreamer

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    08.08.07 @ 01:17 PM
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    Default Schematic for 5150 Combo

    Hi
    has anyone the schematic for the 5150 combo ?
    thanx
    André

  6. #6
    Little Dreamer
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    Default

    As I understand it, the combo bias is fixed at a way better point, and doesn't ned the same mod the head does.

    And GET the JJs!! They rock in my combo! JJ's come standard in the 5150III.

  7. #7
    Eruption

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    Default

    For the schematic, just email Peavey and ask very simply for the schematic for the Peavey 5150 Combo. Don't tell them anything about your technical proficiency or what you intend to do. They should send you one without a lot of hassle. If you open up with a lot of information you might be setting yourself up for an email argument about whether or not you should be doing it.

    As it is, the 5150 Combo is biased a bit warmer than the head and thus, you may hear from some people to simply leave it alone [from me as well]. I agree with this only to the point that the combo is laid out a little differently than the head and its not as easy to grab the circuit board out of the chassis & start working on it.

    I personally think that if you're concerned about the amp's bias you should start by getting a set of JJ power tubes from someone [that are chosen for the appropriate bias] like Eurotubes and see where that takes you. If you simply must adjust the bias to perfection, the mod is pretty easy but getting to the circuit board may be the challenge.

    This document shows how to do it for the head:
    http://blueguitar.org/new/schem/peav...0_bias_mod.pdf
    With a final rev schematic for the combo, this should be enough to get the job done.

    As always, measure twice ... cut once. But don't do this mod if you're uncomfortable doing so. I've worked on many tube and solid state amps and I'm still not entirely comfortable with the concept of digging into my 5150.

  8. #8
    Little Dreamer

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    Default

    Hi
    i like to do a adjustable bias because the bias is to high !!! 55 mA with new jj 6l6 tubes
    i have the same problem with tad 6l6
    can you help me ?

    sorry for my bad english ,i am from germany

 

 

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