I thought all copper was electrically conductive.
"Copper" is pure copper. Anything less than pure would be copper alloy or dirty copper. And yes, you are right. All copper is conductive.
Copper is the second best conductor of electricity after Silver. And here again, both metals being pure.
@ Rocket -- One of the many advantages of using copper tubing as opposed to copper rod is that if you are operating at elevated
frequencies, then you will start experiencing "skin effect" which simply means that the current will be increasingly concentrated,
in direct relationship to the frequency, toward the outside of the conductor or skin of the material.
No need to pay for all of that copper in the middle. Use the money for more tubing.
Also at elevated power levels even copper will start getting hot with too much power. With tubing you can use a cooling medium
through the tubing. Already a common practice.
In post one you state 75 Volts @ 0.5 Amp and in post 6 you state 75VAC @ 2 Amps. That's a big difference.
According to your specs of 75V at 500ma, that is only 37.5 watts for the layman. You didn't specify the frequency of your system.
A DC system would consume more power at the same voltage and current level. Think square root of 2.
Just a little insight into copper as an electrical conductor. Good luck with your project.