I'm not certain that I really need a new ammeter or, if I do replace the current meter, whether I need a shunt. The 10-amp power supply is quite old (1966), but while the DC voltage output is on target, I can't get any response from the ammeter with a good multimeter (Beckman Circuitmate) attached. What makes me think that a new meter would not require a shunt is the fact that the wires serving the meter are 20 ga., less than a millimeter thick. I would think they would evaporate if asked to carry 10 amps. I don't have a schematic for the power supply, unfortunately.

 

Disconnect the ammeter.
If you still get current at the output, then there is a built-in shunt.
But, if so, you would have to match that shunt resistance to the new ammeter.

 

Nada at the front panel 3 Amp output. I'll check the fuses. Is there anything else I should scrutinize? I can also try the 10-amp output at the back.