Tommy's guide is really good. And yes, there were quite a few versions of the frame. One great tip Bruce Felter gave me on Dynasonic bridges follows . . . .
The basic idea is a frame which pre-tensions snare wires via a thumbscrew tightener (think of a medieval torture rack - same principal). But the original design also had a small set screw which allowed the snare to also be bowed up towards the head. (Imagine the prisoner has a spike behind his neck, forcing him to arch his back upwards) Hey! This is fun! If everything is just right, you need almost no tension on the actual strainer to get a nice snappy snare. Genius actually.
The later models (like the Al Drew reproductions from the factory moulds - I am assuming that's what they are) are lacking this screw. CBS cheapskates. Bruce told me to cut a few thin strips of felt from something like a guitar cloth; and glue them to the frame where the wires touch. So when you tighten the screw which holds the snares onto the frame, the snares will bend upwards to kiss the bottom head. I did this with a 70's frame and it worked really, really well. Vale Longroll. Gone; but never forgotten.
