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.