Well, Tube World, the high-end boutique online tube dealer, says the Sylvania metal base is regarded by many as the best US made 6SN7. Many will disagree with that, of course. The metal base are more rare so more expensive.
The metal base and many black base Sylvanias are considered excellent tubes. What is printed on the black base?
The metal base and many black base Sylvanias are considered excellent tubes. What is printed on the black base?