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I used a Toro transformer which puts out 28 volts ac and powers up the toro sprinkler system. i suspect that other brands also use 28 volts. I have attached a photo of mine and you can read the part number. 

But, you only need such a power source if you Kollsman uses an electronic averager which was an upgrade made in the mid 1980's. If you have the original clockwork averager then you can power the light bulbs with small batteries since they do not require the large amount of current demanded by the electronic averager. If you try to run the electronic averager with three 9 volt batteries wired in series then it only lasts for about 15 minutes. 

If you have 28 volt bulbs in your sextant then go to Fry's (no Radio Shack any longer) and get the 9 volt battery clips and wire three in series. A better solution is to replae the bulbs with either 12 volt or, even better, 6 volt bulbs and I have posted the type of bulbs to get. For a 6 volt supply get a four "double A" battery holder. For 12 volts get two of them or wire in a lighter socket plug for your car. See links below.

gl

https://NavList.net/m2.aspx/Sextants-for-use-land-LaPook-sep-2006-g1212

https://NavList.net/m2.aspx/sextant-for-use-land-LaPook-sep-2006-g1211

https://NavList.net/m2.aspx/Kollsman-periscopic-sextant-mount-LaPook-jan-2015-g29903

https://NavList.net/m2.aspx/Kollsman-periscopic-pendulous-sextant-LaPook-sep-2008-g6215

https://NavList.net/m2.aspx/Backyard-Sextant-System-LaPook-jul-2015-g32061

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