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    Re: Bubble sextants on e-bay
    From: Jean-Philippe Planas
    Date: 2007 Jan 2, 22:45 -0800
    Thank you very much Ken for these information.
    JPP

    Ken Gebhart <gebhart{at}celestaire.com> wrote:
    JPP,
    I don’t know that, but whatever it was- a newly manufactured sextant probably met the requirement with ease. The problem occurred over time (not usage) when the lubricant absorbed into the pewter-like material of which the axle was made.  This left a semi dry surface which the (too) small spring holding the worm gear against the sector gear was unable to overcome.  The A-10/ A-10A sextants became notorious as the “backlash” sextants.  When they were used often, they were great sextants. But if they sit around for a few years they will begin to freeze.  Needless to say, almost every sextant for sale on ebay , or a private seller has been subject to this condition.

    Backlash on any sextant should not be a big problem if you always remember to take the reading in the same direction.  However it is a bother to do.

    Ken


    On 1/2/07 3:53 PM, "jean-philippe planas" <jeanphilippeplanas---.com> wrote:

    Just a question for Ken. Does he know what the initial A-10 or A-10A backlash specifications were? Or what is acceptable for a rebuilt instrument?
      
    JPP

    Ken Gebhart <gebhart{at}celestaire.com> wrote:
      

    Alex and others,

    I agree with Robert about the MK IX being good. We used to sell them for a
    while. My high school aged son overhauled them without any problems. There
    were 2 models: an A model which had no averager, and a B model which had a
    large cylindrical averager sticking out the forward end. The wind-up
    averager is really of no use unless you are shooting from an airplane, so we
    just sold the A model. When these ran out, we simply lopped off the
    averager of a B model with a hacksaw, and voila- it became an A model We
    probably have 50 to 100 of these left over in a self storage unit. I would
    be glad to sell some of these for, say- $50 each (which is mainly for the
    effort of digging through them to find the decent ones). For that matter,
    we also have piles of A-10s, A10As and AN 5851-1s too. I probably will never
    do anything with them, so if someone wants to come to Wichita with a
    trailer, I can make you a deal on the lot.

    The A-12 sextant used C size batteries whose covering was a cardboard sleeve
    (during the war). The design was to remove the sleeve and insert the
    batteries. You can still peel off the jacket of modern C cells, and insert
    them. They won't look pretty, but they work ok. If you like you can cover
    them with masking tape.

    Do not under any circumstances buy an A-10 or A10A on ebay (or from anywhere
    else for that matter). Not only are the bubble chambers probably dry and
    hard to fill, but 99% of them are frozen internally, due to poor lubricating
    design. Total disassembly is required to fix this problem. Even if you get
    the 1% that works, it will probably have horrible backlash.

    The AN 5851-1 (also known as the Navy mark V or the A-14) has the raduim
    lighting mentioned earlier, but the paint containing the radium has
    deteriorated over the years such that the radium light cannot get out very
    well. Most of them have 50% deterioration requiring well dark adapted eyes
    to shoot stars at night.

    Lastly, Alex, you prefaced your analysis of CN usage with the phrase "I
    think" Therefore, I can't say you are wrong. However, if you could stand
    in our booth during a boat show, and hear the favorable comments from
    passersby (in contrast to 10 years ago), or see the many people that come to
    our seminars, I think you would feel differently. Celestialis


    On 1/1/07 1:11 PM, "alex" wrote:

    >
    > Dear Robert,
    > Thank you very much for a lot of useful info.
    >
    >> If you are looking for a bubble sextant, there are only two that I would
    >> recommend without hesitation and in this order:
    >>
    >> British MK IX A
    >
    > Do you have any experience with AN 5851-1 (a.k.a. A14) recommended
    > by others? And its development A15 with variable-time averager?
    >
    >> You should purchase it from a reputable
    >> dealer who knows sextants and who has hopefully overhauled the unit you
    >> intend to purchase.
    >
    > I have not seen an e-bay dealer yet who sold an air sextant without a
    > disclaimer
    > that he does not know how to use it. My experience with e-bay so far
    > confirms
    > your example with 10 coins falling heads.
    > Of the 8 items I bought on e-bay so far, except books, 3 had hidden
    > defects and 3 were
    > badly damaged in the process of delivery (and I was never able to
    > collect any insurance).
    >
    >> As for where to find them, there are several dealers out there. Two come to
    >> mind: our own Ken Gebhart and Robert E. White &Sons of Boston
    >> Massachusetts.
    >
    > Robert White's web page does not seem to mention any air sextants.
    > And I did not know that Ken sells any used equipment that is not
    > listed in Celestaire catalog.
    > Ken, how to find out what antique items you have for sale?
    >
    > Alex.
    >
    >
    >







    JPP

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