I think he's seen using Ludwig tambourines a lot, but I'm not for certain.
It would certainly be logical—I read in Modern Drummer of Rhythm Tech's founding, and the Ludwig headless tambourine (in all of its four-pound glory that inspired the original Rhythm Tech tambourine) was cited as being the industry standard during a period which he was active.
Of course, I think many of us have seen the "Unplugged" performance of
Layla, during which Mr. Cooper uses a headed tambourine that has quite a dimple where he's stroking it (upon which one presumes a bit of history with it). It could be Ludwig. Eh, well, it was fun to type.
