Wiring electrolytics-Can I use solid copper?

[Magnavox300]

I am ready to install new electrolytics on a 1960 Magnavox,
and just bought 20 gauge solid wire, which when I spliced it, is copper.
But looking at it, I don't see one piece of copper wire on the chassis.
Is the old wire copper coated in nickel?
Does it need to be? Just want to be sure before I go ahead and solder everything. Thanks!