Fatparrot,
You can also go over to vintagetubservices.com and make your way to the stock list page, then click on octal tubes.
If you read your way down thru the selections and brands,
you will also get a minor description and history of the
differant types.
A proper answer to your question would require a short term
paper on 6SN7's as it would cover the history, require-ments, uses, tooling changes, etc... thru the years. But
Andy puts in some helpfull, and interesting tidbits in the
price list that may help you out.
