Found a 500C recently and it works!

Really nice Fisher. Cool bonus on the extra tubes!

Ken; Fisher 7591's are rebranded Westinghouse's. DAMN good tubes. I've got a quad of EICO's (rebranded Westies) laying around that the bases look like they've been in a war, but test just at the minimum. All 4 will still pull 30ma tops. So I use them as backups to the EH's in my 800C.

Larry