The older balanced regenerators

Apparently out of some design necessity, PS Audo used to make regenerators that actually output balanced AC. When was that, and how would those compare to modern ones?
I’m very intrigued by balanced power and regenerators, so having them in one package sounds very appealing.

i Too would be interested in that, namely using an old pp500 ,obviously generating balanced AC, which - years ago- I did not replace with the premier as that appliance earned a bad reputation here regarding reliability. so how does it compare with say a p12 oer p 15 would be nice to know.