I have a pristine pair of the "nickel" base Sylvania's which I've used in my Modwright 5400 as well as a couple different pieces of Atma-Sphere gear. Too my ears, they're OK but not worth the money some are demanding for them. I have a couple pairs of the black base version and they sound pretty much the same.
If you've got the budget for the old nickel base Sylvania's, I'd stretch it a bit and look for a pair of the old black glass Tungsols. I have a couple pairs of them and out of my collection of around 60 NOS 6SN7's, they're definitely my favorite, by a wide margin.
If you've got the budget for the old nickel base Sylvania's, I'd stretch it a bit and look for a pair of the old black glass Tungsols. I have a couple pairs of them and out of my collection of around 60 NOS 6SN7's, they're definitely my favorite, by a wide margin.