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 Post subject: Triplett 630 Type 5 Calibration Pot
PostPosted: Sep Sat 18, 2021 7:41 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 184
Location: Palm Bay, Florida
Hello again,
I'm finalizing a 630 that I've been going over for my bench. The meter scale plate says it's a 630 Type 5. I was checking accuracy and realized I have a 600 ohm potentiometer on the back of the meter movement housing. It appears to have a resistor on top in blue that say r6096 on it.

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Does anyone know what the pot is for? I've looked in a few manuals and the NA version shows a pot and calls it milliamp adjustment but it doesn't show it in the schematic?

Any help would be greatly appreciated.

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Robb


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 Post subject: Re: Triplett 630 Type 5 Calibration Pot
PostPosted: Sep Sat 18, 2021 5:01 pm 
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Joined: Nov Sun 19, 2017 4:24 am
Posts: 28
Location: Rossland BC
There is no such pot on my 630-PL, just a red wire leading from that connection back to the DC+/AC switch. No cap to the adjacent connector either.
Chuck


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 Post subject: Re: Triplett 630 Type 5 Calibration Pot
PostPosted: Sep Sat 18, 2021 9:51 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2069
Location: Oswego, NY, USA
It should be the DC millivolts calibration trimpot, probably wirewound. The usual calibration sequence is to first check the meter's fullscale microamps deflection, which should match the spec listed in the manual; usually 50ua. Some newer Triplett VOM's might have a movement that has a fullscale deflection in the ~43 to 48 DC ua; so those will have a "selected" shunt resistor to calibrate it to 50ua fs. Many of the older Triplett VOM's do not have a shunt calibration ua resistor where the movement itself was calibrated to 50ua fs. I don't know if your Type 5 would have that extra ua cal shunt resistor; and if you don't see it on the outside, it might be installed inside the meter case. After that, you can adjust this trimpot to deflect the correct/specified millivolts DC fullscale; which should be listed in its manual; usually around 250mv for most 630's. I'd think that the blue resistor you mention should be in series with the trimpot, and they are installed in series with the meter movement, to adjust DC mv. These two items need to be calibrated before starting any of the other calibrations.


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 Post subject: Re: Triplett 630 Type 5 Calibration Pot
PostPosted: Sep Mon 20, 2021 3:01 am 
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Joined: Aug Wed 04, 2021 3:43 pm
Posts: 184
Location: Palm Bay, Florida
Fred Scoles wrote:
It should be the DC millivolts calibration trimpot, probably wirewound. The usual calibration sequence is to first check the meter's fullscale microamps deflection, which should match the spec listed in the manual; usually 50ua. Some newer Triplett VOM's might have a movement that has a fullscale deflection in the ~43 to 48 DC ua; so those will have a "selected" shunt resistor to calibrate it to 50ua fs. Many of the older Triplett VOM's do not have a shunt calibration ua resistor where the movement itself was calibrated to 50ua fs. I don't know if your Type 5 would have that extra ua cal shunt resistor; and if you don't see it on the outside, it might be installed inside the meter case. After that, you can adjust this trimpot to deflect the correct/specified millivolts DC fullscale; which should be listed in its manual; usually around 250mv for most 630's. I'd think that the blue resistor you mention should be in series with the trimpot, and they are installed in series with the meter movement, to adjust DC mv. These two items need to be calibrated before starting any of the other calibrations.


Thank you. I've been so busy I haven't gotten back in the shop in a few days.

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Robb


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