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Thread: How to Bias a Guitar Amp

  1. #1
    LVC
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    How to Bias a Guitar Amp

    Great video tutorial by Mojo Sound describing how to replace and bias tubes in a guitar amp.

    He uses the BiasMaster which is a handy little tool to help you get the amp setup properly


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    Remember you must know the Plate Voltage or else the numbers will mean nothing. Measuring the plate voltage is dangerous unless you know what you are doing.
    U highly recommend the compu-bias for all end users because this gives you the plate voltage, current and the dissipation power all on one digital screen. Good investment for occasional useages, but I've found the probes too weak for everyday useage like what I need. I actually use the TAD bias device the same as in the video.

    Also remember there is no such thing as an exact perfect bias for everyone. 70% plate dissipation is the accepted 'typical' for a Class AB1 negative grid voltage biased amp, but some amps like to be a bit warmer and some a bit cooler as do some players. Playing style and headroom also come in to it.
    A mismatch of 3-5mA on your power tubes can be nice. Perfectly matched and the power stage cancels out any even order harmonics it generates. A slight mismatch gives you 'width' and a shimmer. THat said most power tubes don't stay matched for that long anyway and after 10 or so hours will be a couple of mA apart anyway (One of the reasons your tubes sound better after a a few hours).

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    Thanks, that helps! I never realized a mismatch was prefered.

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    Quote Originally Posted by Carol-AnnAmps View Post
    Remember you must know the Plate Voltage or else the numbers will mean nothing. Measuring the plate voltage is dangerous unless you know what you are doing.
    U highly recommend the compu-bias for all end users because this gives you the plate voltage, current and the dissipation power all on one digital screen. Good investment for occasional useages, but I've found the probes too weak for everyday useage like what I need. I actually use the TAD bias device the same as in the video.
    Great info - thanks. I'm looking at a dual bias tester and these two (Compu-Bias and the TAD) are basically the same price ($215 vs. $225). Do you have a suggestion as to which I go with? I do know the plate voltage on one amp but not on the others. I'm not looking for what you are in a bias meter; I'm just wanting to learn and experiment.

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    Re: How to Bias a Guitar Amp

    The Weber Bias rites are a bit cheaper and also very nice. $120-155 depending on config.

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    LVC
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    Re: How to Bias a Guitar Amp

    I have one --

    The locator pins broke on the first time I used it

    Also there is a problem with them

    Weber Bias Rite cathode current monitor

    I am probably going to spend the cash and get one of these

    Compu-Bias™ Computerized Tube / Valve Bias Meter



    Quote Originally Posted by Page fan View Post
    The Weber Bias rites are a bit cheaper and also very nice. $120-155 depending on config.
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