[thirtiesradio]

Very interesting Joe.
 Fisher biased most of their amplifiers hot to get the most power out of them. They were well designed though and I've found several with perfectly good original output tubes. I have 4 Fisher amplifiers using 7591's which are my personal favorites. I've done the electrical mods to 2 of them and they run very cool. Wish I had a X-101C as the styling is hard to beat. I do prefer the 6BQ5/7189 amplifiers overall sound but they lack the power I like, even with highly efficient speakers. I have had 2 of the more powerful Fisher stand alone amplifiers. I sold one, a SA300 as I prefer Fisher's 7591 based amps. I use a 400-CX-2 preamp with a stand alone 7591 amplifier which is my favorite set up.
I was fortunate to find quite a few NOS Westinghouse 7591's many years ago. Westinghouse designed the 7591 in 1959 and only Westinghouse and Sylvania produced 7591's in the US. All others are relabeled. I know Toshiba produced them out of the US, and maybe others.