I've got what I believe to be a 1920's nickel over brass (mostly brass now...) Duplex snare. There are no markings other than the Duplex stamp on the strainer. One of these days I'll get around to working on it.
I wish I knew the secret to replacing the original wires. I worked on a Leedy & Strupe snare with the same round wires and I don't thing they're on tight enough. Or maybe they sound loose inherently.
[IMG]http://debrajeans.smugmug.com/Music/Duplex-Brass-Snare-Before/i-qqfGtdc/0/M/DSC_0307-M.jpg[/IMG]