Posted by Sorry for putting you on the spot, Steve...I'll B.S. for him, then on May 02, 1999 at 23:01:30:
In Reply to: Conn Tubas, Sousas, and Helicons, et al posted by R B Meng on May 02, 1999 at 14:18:13:
Conn DID make some Helicons, Eb and BBb. The BBb's look to me just like the 14K sousaphones (of the past, but very prolific) with the bell stack coming straight out of the first branch, instead of there being two final elbows with a detachment collar. If you found an old beat-up Miraphone 186 bell (bell flair all cracked up and useless as itself), you could easily (does require skill) cut the stack part of it properly, solder this to the bell flair, and convert a 14K sousaphone into a Helicon, and it would be extremely similar to the Conn "factory" BBb helicons.
I believe that all of the twenty-something models (20J,21J,22J,etc.) were either huge detachable recording bell or detachable upright bell with three or four top-action valves. I think that all of them that ended in 0,1,2,3,4,5,6 were short-action (not 100% sure), and were .770" bore. I would consider these to be 6/4 size tubas, because they are just as big as all of the "York"-style stuff that has that "6/4" designation.
During the era that Conn made these giants, those designations ( 3/4, 4/4, 5/4, 6/4 ) had not yet been "created", that I know of. Conn used descriptions such as "Monster","Wonder", etc. I suspect that these fractional designations were "borrowed" from their creation in the violin family.
An extremely comparable sousa to these 6/4 Conn tubas would be the Conn 20K, body-size-wise (6/4), and it is also "short-action". However, the 20K's sousa's valve section bore size is only .734" (same as their no-longer-made "long-action" "4/4" size 14K sousaphones). Conn also made some long-action 6/4 sousas, both in three and (rare) four valves. In earlier postings, no one seemed to be able to identify these by model #, positively.
This is just from experience. I have no catalogs. Someone else may help you more. Conn made quite a few other models in various sizes that I HAVE seen in old catalog pages belonging to others. I would refer you to the Conn-Greenleaf Collection in Interlochen, Michigan at Interlochen Center for the Arts. If they have a curator, I do not know his name. The trombone/tuba teacher there is Mr. Riccobono. If someone else knows his first and second initials, his e-mail address (substitute for the X's) will be riccobonoXX(AT)interlochen.k12.mi.us Also, make sure that I spelled Riccobono correctly!