I have played many Conn BBb sousaphones over the last forty-five years, including 14K's, 36K's, 20K's, 22K's, a real pre-WWII 38K, and I currently have on loan a Cavalier, which is the mid-30's version of a "student" souzy, which later became the 14K.
1) The 14K sousaphone and its relatives, the Pan-American, the Cavalier, the "lightweight" souzys, etc., all have the .734 standard valve block and usually the 24-inch bell.
2) The 20K (metal) & 22K (fiberglass) souzys have the .734 bore, but with the larger diameter bugle, short throw valves, and the 26-inch bell. It is not the "Grand." That designation is for a pre-WWII souzy.
3) The "real" "pre-cyborg" 36K is the fiberglass version of the 14K with the same valve block and 24-inch bell. The post-cyborg 36K is a re-branded King souzy with the .687 bore, different configuration valve block, and 26-inch bell.
4) the old pre-WWIi 38K is its own souzy. It has a large taper bugle, but different from a 20K, and it has the standard .734 valve block. Most had a 24-inch bell, many had the gold-wash interior. This, along with the 40K and a couple others, were called the "grand."
5) other notable BBb souzys: the pre-WWII 40K is the 38K with four valves; and there were a few "grand jumbo" souzys with even larger bores and bells.
6) No experience with Eb souzys.
Yes, I actually typed this from memory, then went to the Conn Loyalist to get this link:
https://cderksen.home.xs4all.nl/ConnSousaModels.html
