Hello Bubi,
I'm a new contributor to the group as well, but as I've been restoring and using British Air Ministry Mk IX series bubble sextants for about 8 months I thought I would respond to your query.
I have no experience of any other bubble sextants, but I have bought four Mk IX series instruments (three of them from ebay) and have got two of them working well on the ground. When they work, and especially if have retained their factory calibration settings, they are excellent instruments. (Beware though. Any Mark IXA you buy will almost certainly need some restoration work. Given the sorts of conditions in which ebay Mark IXs reached me, it's worth mentioning here that I found list-member Bill Morris's ('engineer') illustrated restoration manual invaluable, in describing how to strip the instruments down and perform a wide range of repairs, and the author's after-sales email support is exemplary. It is aimed principally at users of the common Mark IXA model, the first in the series to have a clockwork averaging device essential for use in the air, but the author has recently written an Appendix covering the earlier, pre-1941, Mark IX instrument.)
Like any sextant, buying Mk IXs on ebay is a very risky and sometimes costly business, and I had to purchase three ebay sextants to make two that work. Fortunately, these work extremely well, and I've had a huge amount of fun with them. Whenever I buy one I always ask the seller to confirm that 1) both mirrors are good, 2) all knobs wheels and levers move and 3) that (if a bubble can't actually be formed) the bubble chamber has at least some of its liquid left in it. (The latter because, when fully dried out, over time the sealed chamber glasses may become opaque on the inside; and while it isn't all that hard to refill and reseal the units, their glasses are extremely difficult to open. clean and reseal without special equipment and skills. My first ebay one was like this, and it stayed unusable for a long time!)
It is interesting to read of your background in aviation: as part of my learning-process in using the Mark IX, I asked for help, and was contacted by more than 20 ex-RAF navigators (covering the service period 1942 to c.1980) who trained on these instruments and often used them, most of them post-war. I was told that while they were hardly ever used by Bomber Command navs on operations, Coastal and Transport Commands found them indispensable, especially on long ocean and desert trips.
Hope this helps!
Ian Payne
> Date: Thu, 3 Jul 2008 17:14:21 -0700
> Subject: [NavList 5658] Bubble Sextant
> From: benjaminriecken@hotmail.com
> To: NavList@fer3.com
>
>
> 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
>
>
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