Lookls like it might be a Royer to me.

http://www.royerlabs.com/products.html

Yeah....Royer....could be a Cascade ribbon...They have one in the same type of casing as the Royers

It sounds lovely on that cab whatever it is. I think it sounds like it has the same response as the mic that was used on that track by John Mayer that was being discussed a week or so ago. Everyone voted SM57, but it didn't sound like an SM57 to me, it sounded more open, more like this.