Old Panel Meters

[Bob Jackson]

I bought several OLD panel meters at a recent hamfest. All are DC milliamp types in the range 30-500 mA full scale. I've taken the movements out of each to check the works before attempting to apply any voltage and all seem to be OK, i.e. pointers move freely, no signs of rust, corrosion broken connections, etc (cases are battered and filthy so I thought I'd better look).

My question  is this, not having any prior experience with same, is it correct that these old (some with military markings) have internal resistances that are VERY low, e.g. ranging from  0.4 ohms in the 30 mA one to about 4.5 ohms in the 500 mA one, with the other ranges in between (all measured with a very high quality DMM)? What sort of shunts (or multiplier resistance in the case of voltmeter applications) do you use with such low internal resistances? For example, using the 30 mA meter in a 3A AC circuit (full scale reading to mean 3A)?

I got these CHEAP (and they look really neat!) but I'm a bit baffled by the low internal resistances. I've reused meters before, e.g. from defunct test equipment) but those internal resistances were a LOT higher.

Thanks,

Bob  AG5X

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