I guess my contribution to this thread will be a pointer to a back-issue of Vacuum Tube Valley magazine. The Sping 1999 issue, issue #11, has 6SN7s as the primary cover story, with a multipage article on their history and development, harmonic distortion ratings for most/all of the NOS variants, and a page of listening notes. 7 pages of text and photos in the article.
It is about $15 plus shipping.
http://www.vacuumtube.com/
It is about $15 plus shipping.
http://www.vacuumtube.com/














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