I remember not that long ago (15-20 years back) when folks in OUR hobby were literally kicking these things to the curb. This was when the vintage Fisher community began and ended with the tubed greats. I would be able to pick up a 440, 600, or one of these 500s, for the cost of the gas to come and get it. People were ignoring them in the gap between the tubed era and the Japanese units of the early '70s. Because of their age and the fact that they were the first of the breed, many needed work early (particularly the 600s), which turned off collectors. Their unique "orphanesque" styling probably didn't help them, either. But under the hood and through the speaker jacks, they stand out. They were designed by the same engineering teams that created the wonderful tubed models, and had to please buyers used to the sound of the latter.
It's good to see these first gen SS units finally get some admiration. I've had a restored 220T in my office now for over a decade, and it plays every day. This particular 220 sounds better than our Marantz 2230. They can be reliable daily runners with some effort, and the sound is not far off from the legendary tubed models. Inside, other than some early pcb issues, they are as well built as the tubed classics, with parts sourced from many of the same premium US and European sources.
Be sure to recap it very thoroughly. And also be extremely careful about shorting or overloading the outputs. Most of these models had no meaningful overload protection. The outputs are fragile and can be quite expensive in matched pairs, and as you move up the line, there are more to cope with.