It looks like there should have been some sort of lens or something over the opening but there is no indication that anything was ever there. There are no marks or scratches around the hole from anything ever being there..
If I could see a photo of the dial of a Champlain radio then I might get an idea of what should be there.. if not I probably will put a colored gell behind the opening.. I still have not found out the reason the geared wheel is there..
I guess I will keep looking ..thanks for the interest…Dan in Calgary