rescaling russian meter

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

1. SV2SBEHam MemberQRZ 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. KD0CACHam MemberQRZ 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. SM0AOMHam MemberQRZ 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

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4. SV2SBEHam MemberQRZ 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. SM0AOMHam MemberQRZ 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

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6. SV2SBEHam MemberQRZ 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. WA7ARKHam MemberQRZ Page

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8. W9WQAHam MemberQRZ 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. K8ERVHam MemberQRZ Page

Be sure to use high-quality scratch.

TOM K8ERV Montrose Colo

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I only use Purina scratch for my laying hens.