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Thread: Just made my own bias probe

  1. #1
    GuitarArtologist kmcguitars's Avatar
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    Default Just made my own bias probe

    Weber and Hoffman amps both offer D.I.Y. Bias probe kits. The weber kit inclued 3 resistors for some more options like reading plate voltage from pin 3 and cathode current from the DCV setting on your meter?? Well...I must have done something wrong? Cuz' I couldn't get any plate voltage reading? And the bias was way off? So being that the resistor values are 1 ohm,1 Meg and 100 ohm I figured had a brain fart. So I opened it back up and double checked. Everything looked fine? So after the third time I said screw this!
    I opened it up again cut the resistors out and wired it the Hoffman way. Yeah ! Now it works !! The good old KISS method Keep It
    Simple Stupid
    BTW, Yes...I know I'm lucky I didn't electrocute myself. I did double check myself B4 hitt'in the power.

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    Ultimate Tone Slacker wixedmords's Avatar
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    Default Re: Just made my own bias probe

    That's cool KMC. I am glad it worked out for you.

    I have had pretty good luck with the SRS stuff off Ebay (Hate to bring up Ebay).


    I am taking it for granted the kit is for 8 pin tubes.

    Great information though.
    Jackson, Ibanez & Ovation Guitars
    Laney, Marshall & Peavey Amplification

    ((tube max dissipation wattage / amp plate voltage) x % of max dissipation wattage) x 1000 = bias current in mA

    "There was never a horse that couldn't be rode, never a man that couldn't be throwed." - Marshall Matt Dillon - GUNSMOKE (1959)

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    GuitarArtologist kmcguitars's Avatar
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    Default Re: Just made my own bias probe

    Quote Originally Posted by wixedmords
    That's cool KMC. I am glad it worked out for you.

    I have had pretty good luck with the SRS stuff off Ebay (Hate to bring up Ebay).


    I am taking it for granted the kit is for 8 pin tubes.

    Great information though.
    Yup ! It's for a 8 pin. It's pretty simple to make (The Hoffman way) And Less than half it cost to buy a SRS.And the same Exact thing IMO. You just wire pins 1 thru 7. Drill a hole,solder one end to pin 8 base the other to pin 8 top.
    run it out to you MM set for DCA.Hoffman Bias Probe

  4. #4
    Ultimate Tone Slacker wixedmords's Avatar
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    Default Re: Just made my own bias probe

    Looks great KMC. I agree, it is very easy to build.

    Great information for the do-it-yourselfers. Now when someone asks about a low cost bias solution, this is it.
    Jackson, Ibanez & Ovation Guitars
    Laney, Marshall & Peavey Amplification

    ((tube max dissipation wattage / amp plate voltage) x % of max dissipation wattage) x 1000 = bias current in mA

    "There was never a horse that couldn't be rode, never a man that couldn't be throwed." - Marshall Matt Dillon - GUNSMOKE (1959)

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