Change bore to cut BBb to CC?

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Posted by Mark in Ohio on January 28, 2001 at 22:19:08:

Hello all.

An idea occures to me some time ago for an "easier" conversion to CC tha just might work on small bore BBb horns. I'm looking for advice from the real techs out there, and to see if this has been done before.

I've got a lil' Conn 12J (.660" bore) that is going to have a .750" rotary 4th added downstream, well after the main slide (the post-slide taper of the horn is pretty gradual).

When considering this idea, I located the spot where the bore hits .750". It happens to be (give or take an inch) 29 inches AFTER the main slide.

One would only have to remove roughly 24" to bring it up to CC....If one were to replace the valveset with another that ends up at .750 before (or after) after the main slide, One could convert the horn to CC without having to cut and re-taper all those branches.

Possible valveset candidates that meet this criteria are numerous: The new Conn 52J, The old Conn short-action 2xJ, and many others (the .750/.748" piston seems popular these days).

Of course, the overall taper of the horn would now be considerably different, with expansion concentrated in the leadpipe, which presently exists after the valves. However, this overall taper would not be unlike that of the lovely-sounding old Conn 14K: short leadpipe, ~.735"(?) bore, but a rather gentle horn taper that doesn't really flare much until after the bell collar. Blows 'open', but sweet-sounding and controlled.

What sort of intonation problems might this sort of conversion produce, and can the intonation be tweaked by judicious leadpipe and mainslide design?

I miss having a CC (sold mine a while back, planning to a reality check after leaving the military; $$$) While I definately will add a 4th valve, I don't necesarily plan cutting to CC, nor am I seeking to get zapped by the anti-cutting crowd.

I'm just fascinated by the possibility of this design approach to making a CC, and would love some feedback from the experienced techs out there (Matt, Sam, Joe, et al). Obviously this approach wouldn't work on a 4/4 horn that reaches .750" much sooner than the 12J does.

Mark "FWIW, I'm not cutting my York" Mazak

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