Converting Bb to C, need input!

Discussion in 'Horns' started by prof5, Mar 4, 2005.

  1. prof5

    prof5 New Friend

    Mar 4, 2005
    I'm about half done converting an old Bb Elkhart trumpet to C, but I need some input. I've shortened the leadpipe & bell, and am quite happy with the results - tuning and intonation are pretty good. Now it's time to do the valve slides. Any thoughts on a good way to calculate how much to shorten them? By math it should be about 12%, but I'm not sure.


    ps Yes, I know this is a crazy project, and I don't expect much. I am a professional tech though, so the mechanics of it are no problem. It's the math I'm not sure about! :-?
  2. Robert Rowe

    Robert Rowe Mezzo Piano User

    Dec 24, 2004
    Hello, Garry --

    I've wondered about the same thing.
    I'm a "semi-pro tech" (I'm mainly a luthier ... and my wife is a NAPBIRT "techie" with the tools & such, so I do some horn work).
    I have a few "candidate" horns I think might be useful as "crash-test dummies" (they're not worth salvaging, save for parts).
    Before I take out the 'ole hacksaw ... anyone "out there" able to give us some guidance as to the mathematics of it all ...(??)

    Robert Rowe
  3. eclipse trumpets

    eclipse trumpets Piano User

    Oct 24, 2003
    Hi Guys

    There is no hard and fast mathematical solution to this at all i'm afraid.

    Each Bb as you know has a different set up and as such will need a different length of mouthpipe,Bell and slides to get her into tune and enable the slotting to be right.
    I usualy start with taking around 8% of length from the horn as a point of reference, then its the old bit by bit method on each part to get it correct.
    It may well end up that you have in fact taken a total of 12% off, but i like to start small and have the safety net of knowing that i have enough tubing to work with.

    Of course once you have done this to a certain model then you have a reference point for then next same model! as long as you have taken down the measurements of what you have done of course :D , which i have forgotten to do on a couple of occasions.
    This is ONLY a reference point though as even the same models of Bb can vary slightly, so always be very careful to not dive in with the exact measurements of the last correct conversion.

    REMEMBER !!! taking another mm off when you are still too flat is an awful lot easier than adding tubing/length when you have been over anxious to get the job done by taking far too much off.
    Of course you can always pull the tuning slide out further to compensate for it being too sharp, but you don't have too much length on a C to mess about with before it starts to throw out the intonation.

    Slowly does it every time in my opinion

    I am sorry to tell you that there is no other easy solution to this.

    Once you have done a few you will start to get a feel for what is needed to balance the horn off.

    Best Wishes

  4. eclipse trumpets

    eclipse trumpets Piano User

    Oct 24, 2003
    Oh forgot to mention!

    I like to leave the leadpipe a little longer if i can than the normal standard bach C model as i think it improves intonation by having the longer amount of taper in tact.
    You can achieve this by slightly reducing the bell length to compensate for the added length of the leadpipe
    We are only talking an extra 15mm or so overall! if you can achieve this by leaving the full 15mm on the leadpipe then thats great, but sometimes this has a habit of positioning the leadpipe too far back at the reciever end.
    So maybe you could split it and use an extra 7.5 mm onto the leadpipe itself and another 7.5mm at the bottom of the tuning slide.
    This will add up to your extra 15mm in total and then you can cut the bell a little shorter.
    But as ive mentioned in the previous post, try out before you cut the bell and only take mm's at a time to get the horn back in tune.

    I think you will find the intonation is superior this way!

    Try it as an experiment on an old horn you have lying around first.

    I hope this helps a little?

    If i have confused you in the way i have described anything then feel free to email me for further explanation.

    Best Wishes and good luck

  5. prof5

    prof5 New Friend

    Mar 4, 2005
    Thanks Leigh - you've been very helpful.

    I shortened the 3rd slide 8% initially, ended up at about 10% to be in tune. 1st & 2nd slides worked out fine with no modification. My victim is an old "Elkhart - Built by Beushcer", and intonation wasn't the best when in Bb, so it makes some sense that the mods weren't uniform.

    I'll let some friends play it tomorrow and get their impressions. All in all, a very fun project. Now I'm ready to try it on an Ambassador cornet!

    Thanks again,

  6. mike ansberry

    mike ansberry Forte User

    Dec 30, 2003
    Clarksville, Tennessee, U
    This is really interesting stuff. A friend told me last week that he is going to send me plans for converting an Olds Ambassador Bb trumpet to C. Now all I have to do is get my hands on an Ambassador.
  7. felix c

    felix c Pianissimo User

    Dec 5, 2003
    Puerto Rico
    Dear friends;
    interesting topic
    my trumpet teacher give me a 229 Strad bell. from 70's. Its excellent. im waiting for a 25A leadpipe, anf buy at ebays a Bundy II trumpet to install the pipe, bell and short the slides. The reason its how much cut all.
  8. TotalEclipse

    TotalEclipse Piano User

    Mar 2, 2005
    Brisbane in OZ
    I was wondering if anyone had tried to make a Bb to C Ambassador conversion using a cornet valve set? A sort of larger bore.....
    If you have to shorten some of the bell it must be bigger than 0.460" bore at the cut line.
    Just a thought

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