Charger Specs for Rockwell 74k Calculator

[rprosperi]

I recently acquired a nice Rockwell 74k calculator, which appears to be from May '76. The original batteries are still in-place, and incredibly have not leaked and will still take a charge for a short while. The seller posted pics of it running, though when received it would not turn on.

Does anyone have one with the original charger to confirm the proper Voltage and polarity (I presume tip-positive and probably either 3 or 6V, as these were the most common at the time.) The machine uses 3 x AAA, NiCd 1.2V, 180mAh cells, which will be replaced once the unit is properly tested/verified. The jack is the smaller RCA type (I think this is a 2.5mm jack).

All info appreciated.

p.s. Thanks to Gene for pointing it out.