rescaling russian meter

Discussion in 'General Technical Questions and Answers' started by SV2SBE, Jun 15, 2019.

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  1. SV2SBE

    SV2SBE Ham Member QRZ Page

    Hello, im working on a russian amplifier and need to replace one of the meters. The original is a 5A dc meter and broken. I found one 1A meter new and with the correct face. My problem is how to calculate the shunt resistor for this to use it as a 2A meter. I have meters with my multimeter full movement at 0,6 volts and resistance at the 200 ohm scale be at 003!
    any help here please, because im little confused.

    Thanks
    George
     
  2. KD0CAC

    KD0CAC Ham Member QRZ Page

    This web site has a program for printing scales , 2nd down the list - http://tonnesoftware.com/
    A good video about meters repair etc. -
     
  3. SM0AOM

    SM0AOM Ham Member QRZ Page

    It is very simple to calculate the shunt to get the 1 A meter to show 2 A FS.
    Just make a shunt with exactly the same value as the internal resistance of the 1 A meter.

    However, to determine the internal resistance can be tricky, as measuring such small values is hard to do.

    The obvious solution is to connect a small power supply in series with the 1A meter and a limiting resistor, adjust the voltage so the meter shows full scale, and then add a shunt which is adjusted so the meter reads half scale.

    73/
    Karl-Arne
    SM0AOM
     
    KI4AX and KD0CAC like this.
  4. SV2SBE

    SV2SBE Ham Member QRZ Page

    shunt need to be a wattage resistor? or i can use a multiturn trimmer to get the results that i want and keep it as a shunt?
     
  5. SM0AOM

    SM0AOM Ham Member QRZ Page

    The shunt will dissipate only milliwatts, so any resistor would be sufficient.

    A problem with a trimmer is that it usually has a minimum resistance that would be much higher than the value required.

    Mostly, such problems are handled by making the shunt out of a piece of wire adjusting its length for the proper value.

    73/
    Karl-Arne
    SM0AOM
     
    SV2SBE likes this.
  6. SV2SBE

    SV2SBE Ham Member QRZ Page

    so i need so low resistor, i will see if i can play with some parallel resistors to see what i can do
     
  7. WA7ARK

    WA7ARK Ham Member QRZ Page

    KD0CAC likes this.
  8. W9WQA

    W9WQA Ham Member QRZ Page

    i once had to shunt a "meter"? for 25 amps. i cut about 18 inches of #14 as a first trial to calculate the final. it was close enuf !!! such luck...
     
  9. K8ERV

    K8ERV Ham Member QRZ Page

    Be sure to use high-quality scratch.

    TOM K8ERV Montrose Colo
     
    WA7PRC, AD5HR and KD8DEY like this.
  10. AD5HR

    AD5HR Ham Member QRZ Page


    I only use Purina scratch for my laying hens.
     

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