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1% tolerance metal film resistors measuring different

Discussion in 'Shock Brother's DIY Amps' started by itsGiusto, Sep 7, 2020.

  1. itsGiusto

    itsGiusto Tele-Holic

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    I keep on ordering supposed 1% tolerance 1 ohm metal film resistors, for the purpose of having an easy bias measurement on the cathodes of my fixed-bias amps. However, despite the fact that I've ordered these several times, they never end up actually measuring 1 ohm on my meter, usually more like 1.3 to 1.7 ohms.

    Is the problem that the resistor is not actually 1% tolerance, or is my meter likely inaccurate at that small range? Not knowing which it is is annoying, because I never know if I should adjust for this and divide by 1.3 when measuring the bias. If the resistors are bad, can anyone recommend a reliable place to get 1% tolerance 1 ohm resistors?
     
  2. rz350

    rz350 Friend of Leo's Ad Free Member

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    Check your meter leads, it's common for two wire ohmmeters to have a bit of resistance from the leads.... Short them together and see what it reads, it's common to have near an ohm of resistance from just the leads.

    ...or get a 4 wire Fluke, that's what I use.
     
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  3. Nickfl

    Nickfl Friend of Leo's

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    Or get an ESR meter. They're made to be very accurate at low resistance and it's a worthwhile addition to you amp maintenance tool box.

    My bet is that your meter isn't up to the task rather than you having constant bad luck with resistors.
     
  4. itsGiusto

    itsGiusto Tele-Holic

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    If it is a problem that the leads have inherent resistance, does that mean that I can't trust my bias voltage measurement as well because of that? Or would voltage measurements be more reliable than resistance measurements?
     
  5. DavidP

    DavidP Friend of Leo's

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    Get some 1% 10ohm resistors, easier to find ones very close to spec, then divide by 10 in your bias calcs.
     
  6. tubegeek

    tubegeek Friend of Leo's

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    If you doubt your meter, just connect 10 of the resistors in series and see what you get. 10.3? Or 13?
     
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  7. DougM

    DougM Poster Extraordinaire

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    Most meters have a way to zero the ohm function by holding the two probes together and then pushing the zero button, to mitigate the resistance of the probe's wires.
     
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  8. rz350

    rz350 Friend of Leo's Ad Free Member

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    No, because the resistance of the voltage measurement circuit is probably in the megaohm range, so series resistance will have almost no effect on it, but series resistance will have an effect on low ohm measurement, and current measurement if you put the meter in series with the circuit.

    What kind of meter do you have?
     
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  9. rangercaster

    rangercaster Poster Extraordinaire

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    This topic reminds me of why I don't build amps...


    I buy them and bring them to the shop when they stop working...

    I'm lazy ...
     
  10. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    A lot of meters have trouble measuring very low resistance. Try it in series with a 100ohm resistor. 101ohms?

    You can try several of them in series like tubegeek said.
     
  11. kbold

    kbold Tele-Afflicted Silver Supporter

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    What meter do you have ?
    And what is it's minimum ohms range?
     
  12. Musekatcher

    Musekatcher Friend of Leo's

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    My old ones have a pot, and a VU meter screw for calibrating and zeroing. My 90's Radio Shack is auto-zeroing, very useful. My newer cheapies don't have a zeroing function that I can find?
     
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  13. itsGiusto

    itsGiusto Tele-Holic

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    I have an AideTek VC99+
     
  14. warrent

    warrent Friend of Leo's

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    Try this from your meters manual:
    NOTE: At range 600 Ω, short-circuit the test leads to measure the wire resistance and then subtracts it from the real measurement. Or press “”REL” to clear the wire resistance and read the value directly.

    http://www.aidetek.com/New_products_info/Datasheet/Vichy/VC99+.pdf
     
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  15. Digital Larry

    Digital Larry Friend of Leo's Gold Supporter

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    Unless the same resistor measures different values on different days, I'd say the meter is "accurate" if not "calibrated", if that makes any sense. I'm not sure that mine does fractional ohms anyway. I did measure 3 ohms on a shorted pickup recently which struck me as odd, but I suppose it's possible.
     
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