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    Re: Bubble Sextant
    From: Ken Gebhart
    Date: 2008 Jul 14, 17:43 -0500

    Just a note on filling vapor bubble chambers.  The Tech manuals
    require a vacuum chamber in order to degas the xylene of air before
    introducing it into the chamber.  We found that filling the chamber
    with airy xylene then turning the diaphragm to make a bigger bubble
    works somewhat well.  Doing this 3 or 4 times, and introducing more
    xylene each time will result in a bubble that may be a little hard to
    remove from the field of view when desired, but is acceptable.
    
    Ken Gebhart
    On Jul 11, 2008, at 12:40 AM, engineer wrote:
    
    >
    > The British Mk IX is about 200 grams lighter. and is  my favourite
    > because all the controls come readily to hand, it is easy to use and
    > read and you have a reasonable chance of getting one that works. With
    > the exception of the averager on the Mk IX A, the works of the Mk IX
    > series are accesible and usually easy to fix. The bubble assembly is
    > also easy to refill.
    >
    > My A7 has a vapour pressure bubble chamber which, if empty when you
    > get it is very difficult for the non-specialist to refill. Many of the
    > WW II US instruments suffered from "complification" and some used 4
    > prisms, heavy and expensive to produce. The AN 5854-1's
    > averager(strictly, a median device)is temperamental and hard to fix if
    > it has suffered corrosion in storage. The AN 5851(Navy Mk 5)is heavy
    > and clunky and initial setting of its averager needs care. The A10-A
    > is perhaps the handiest instrument to use, provided the electrical
    > marking system is in good order. It is not impossible for
    > a reasonably handy person to fix the system, once it has been
    > understood. The A10 uses the Mark I finger to operate the marking
    > pencil. That leaves rarer instruments, like the A8-A and the Navy Mk
    > IV. The latter was plainly not a success and if you find one, the
    > averaging system will tax the average person to fix. The A12 is a
    > favourite of many people and was designed to be cheap to produce(some
    > of the others cost almost the price of a small home to produce). The
    > arc and vernier on mine are poorly cut, but if you can get one free
    > from corrosion and in working order it would be a good one to start
    > with.
    >
    > The Achilles heel of nearly all the bubble sextants is the bubble
    > chamber. For practical purposes, you cannot refill a vapour pressure
    > chamber. Happily, most of the later bubble sextant produced used a
    > different system with an air reservoir; and these are fairly easy to
    > refill. The MA series are, alas, expensive and do not often come on to
    > the market.
    >
    > Bill Morris
    >
    > On Jul 11, 1:54 pm, "Gary J. LaPook"  wrote:
    >> My fravorite is my MA-1 which isn't a bubble sextant but a pendulous
    >> mirror type and my second favorite is the MA-2 with a bubble. If you
    >> want a light, simple sextant get a Bendix A-7, it is the lightest
    >> bubble
    >> sextant I have.
    >>
    >> gl
    >>
    >>
    >>
    >> glap...@pacbell.net wrote:
    >>> Here is a link to a site with discriptions of many types of bubble
    >>> sextants:
    >>
    >>> http://home.earthlink.net/%7Es543t-24dst/airnav/index.html
    >>
    >>> gl
    >>
    >>> On Jul 5, 3:19 am, glap...@pacbell.net wrote:
    >>
    >>>> You should also check the files section of the Yahoo sextant
    >>>> group for
    >>>> more information on sextants.
    >>
    >>>> http://groups.yahoo.com/group/Sextants/files/
    >>
    >>>> gl
    >>
    >>>> On Jul 3, 5:14 pm, bubi352  wrote:
    >>
    >>>>> I am new to this group and new to celestial navigation. I
    >>>>> currently
    >>>>> work as an airline pilot and fly extensively over water at
    >>>>> night. I
    >>>>> have developed a keen interest in determining my position the old
    >>>>> fashion way.
    >>
    >>>>> Could someone tell me which bubble sextant I should buy?
    >>>>> What should I be looking on a bubble sextant?
    >>>>> Where can I buy one?
    >>
    >>>>> Thank you in advance.
    >>
    >>>>> Bubi- Hide quoted text -
    >>
    >> - Show quoted text -
    > >
    
    
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