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Varisistor ratings in a Fluke 8010A bench meter

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  • Varisistor ratings in a Fluke 8010A bench meter

    In my quest to stay alive, I left my bench meter connected to an amp was working on to monitor the B+. In my infinite wisdom, I connected it to the plate pin on one of the power tubes and then proceeded to test it at full power into a dummy load. Well, that has resulted in popping R2 and all of the Varistors (VR1 thru 3) at the input. Woops. Looks like I won't do that again. So here's my quandary: finding replacements for the varisistors.

    See the attached PDF for support info for the following:
    The manual specifies part number V430MA7B, 430v, +/-10%
    Mouser carries said part, from Littlefuse, but it is listed as a, 275V, 100A, 11pF, part on Mouser's site. Well, that seem a little odd, but ok, lets look at the datasheet.
    The datasheet specs 265V AC RMS continuous, but 430 VN(DC) @ 1ma, which I presume means 430v nominal DC voltage at 1 ma.

    If I take the part number from the part itself, 430M7B, I get nothing. And if I just search Mouser for 430v varisistors, I get parts, but I'm not sure they're sufficient.

    So, am I correct that the Littlefuse part is sufficient and that I'm deficient in understanding the ratings of varisistors? I presume that the part number being the same means that Littlefuse probably consumed whatever company originally made this part and just carried the part number forward with the same ratings, but I've been surprised before.

    Lastly, is there anything else I should test while I'm in there fixing stuff? I get can get DC voltage readings on the meter, they're just low. I presume because the varisistors are conducting and dragging down the signal, but I don't know their failure mode so I may be wrong here and trying to fix a sinking boat with duct tape.
    Attached Files
    -Mike

  • #2
    Looks like it's the correct part.
    By the way, nice resistor!
    I can't recommend other components to check with only that partial schematic.
    Do you have the full schematic that you can post here?
    1937 Gibson L50 "Black Special #4"
    1978 Gibson Melody Maker D Reissue
    2004 Ibanez SZ720FM
    Epi SG '61 with 490R & 498T Pickups
    Couple Marshalls, Crate Blue VooDoo
    Couple 4x12 cabs
    Couple Orange combos
    TONS OF FREAKING TEST GEAR- SCOPES, METERS ,ANALYZERS
    SIG GENS, ETC, ETC, ETC.





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    • #3
      Yea, I'm a little proud of that one. First resistor I've ever turned into a munition. I jumped a little when it exploded.

      There's no loose version of the full schematic, it's at the end of the manual, PDF page 78. You can try this link:

      http://www.google.com/url?sa=t&rct=j...95039771,d.b2w

      Or the top links in this search: https://www.google.com/search?q=8010...utf-8&oe=utf-8
      -Mike

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      • #4
        Fluke themselves have the parts available.

        The resistor is a bit salty.

        Replacement Parts | Fluke

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        • #5
          If it were a Guitar amp I'd get a Mouser equivalent and call it a day, but on a measurement/test device I'd go for the original part.
          Of course, it's your decision

          PS: I'd also ask for the test procedure for checking or recalibrating measurements.
          Plain "working" is not enough here.
          Juan Manuel Fahey

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          • #6
            Thanks for the help gents. I was not aware Fluke stocked parts, so I'll get with them and see what shakes out.
            -Mike

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