William C. Ray wrote:
>I'm looking for a reasonable source of tube characteristics & an
>equivalency chart. The proximal reason is that I seem to have
>acquired an ancient Fisher receiver which is missing a `7868`

The 7868 is very close to the 7591 and 6GM5 electrically. The 6GM5
is a 9 pin also, but not pin compatible. There is an article by
Gary McClellan in Glass Audio, April 1996 ("Yes, You Can Substitute
for the 7591 Tube!") that compares these tubes and a couple of others.

You can find a little data about the 7868 on my web page:
http://www.phy.ohiou.edu/~cigna/tubes/sheets/

-- Dave Cigna

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