Pianotech

  • 1.  Yamaha C7 and C7B differences

    Member
    Posted 05-02-2016 23:53

       Does anyone know about the scale differences and angles of the hammers of these two models. The C7B is 1981 vintage . I got a set of C7 hammers from a colleague all prehung but the angles in the bass went just a little to the right and not folloowing the angle of the existing hammers. The existing hammer angle in the tenor starting at note 21 go to the left. Number 22 in the replacement set goes to the right . Following is the number of hammers per section:

    Bass 1-20 Tenor 21-50 Low treble 51-70  High treble 71--88.

    Obviously I am going to have to send samples out to get new H/S/F and the correct angles but would like to know what gives and if there was a changeover to more notes in the bass and a change in angles.

    I had to do a tracing to get a custom made string cover done because the cover maker said a C7 cover would not fit.

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    James Kelly
    Pawleys Island SC
    843-325-4357
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  • 2.  RE: Yamaha C7 and C7B differences

    Registered Piano Technician
    Posted 05-03-2016 00:02

    If you wanted to substitute a lot of labor for a lot of money, you could use Jurgen's invaluable hammer head extracting pliers, the tapered reamer in the tap wrench handle, and the Titebond molding and trim glue, and rehang what you've already got, only at the correct angles this time, plugging and reboring those which are too far off to adapt.

    It probably doesn't sound worth the time and effort, but a set of hammer is a set of hammers, if you fix the hammer boring you get the existing shanks for free instead of having to buy new, and experience is worth something. I've done some things like this just to correct my own mistakes.

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    Susan Kline
    Philomath, Oregon

    Original Message


  • 3.  RE: Yamaha C7 and C7B differences

    Registered Piano Technician
    Posted 05-03-2016 06:40

    I can't give you explicit details on the C7B, but can tell you that the C7 model has floated in lengths from 6'10' to 7'4" as they tweaked their scale over the years. The length will determine the bass string angle scale which goes to the heart of the bass hammer angles. 

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    Tom Servinsky

    Original Message


  • 4.  RE: Yamaha C7 and C7B differences

    Posted 05-03-2016 07:09

    A few degrees in rake should not matter as long as the strike point encompasses the width of the unison.

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    Regards,

    Jon Page

    Original Message


  • 5.  RE: Yamaha C7 and C7B differences

    Posted 05-03-2016 08:20

    Are you saying that there is a differing number of bass notes between the pianos? You could remove the extra bass hammers at 22+, plug the holes and redrill for the tenor rake. Or, you could remove the lower few hammers and place those shanks at the top end with new treble hammers, if the shanks are the same thickness.

    In any case, verify their correct length. Measure the string height, measure the Hammer Center Height. Subtract HCH from SH, that should be your bore distance. You could also install a few across the compass and bring them to the string and check with a hammer square to see if they would strike properly.

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    Regards,

    Jon Page

    Original Message


  • 6.  RE: Yamaha C7 and C7B differences

    Registered Piano Technician
    Posted 05-03-2016 08:02

    Around the early '80s The C7 switched from 20 bass notes to 23 bass notes. You probably don't want to try hanging bass hammers in the low tenor.

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    Karl Roeder
    Pompano Beach FL

    Original Message


  • 7.  RE: Yamaha C7 and C7B differences

    Posted 05-03-2016 08:33

    Karl's right, the tails on the bass hammers are squared for the bass rake and might not allow for re-arcing for the tenor rake. Loose the lower 3 notes and install whatever you need for the top 3 note in the treble. Just make sure the 'new' set strikes properly and are not pitched back too much.

    I recently replaced a set on a C7. The OEM hammers were pitched back about 3 degrees and were way short of the SH-HCH parameter. They were still understriking by a good amount even in their worn condition. In their new state, they had to be severely understriking. I replaced with a hammer bore as mentioned and 90 degrees to new shanks. The piano sounds better than ever. The shanks are a few mm longer due to the 90 degree pitch while maintaining the Strike Point and work fine with the tails arc'd to 2.75" centered on the shank.

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    Regards,

    Jon Page

    Original Message