A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robert Swartz
Date: 2015 Dec 28, 22:09 -0800
All WWII U.S. bubble sextants that have an external battery case and cable plug w/ center pin work as follows:
Bendix and B&L sextants: Center pin carries +3V potential. Outer ring carries -3V potential from 2 D cells. Instrument frame is negative (chassis) ground.
If you have voltage out of your battery case (verified w/ a meter) but no lights--oftentimes you have poor or no ground conductivity
due to corrosion in the instrument or screws holding parts together. Clean corrosion and voila--lights (of course check bulbs and switch).
A-10A sextants use a battery case w/4.5V potential from 3 D cells which drive the solenoid of the mechanical averager and have a resistor for 3V lighting.
A-10 sextants use 2 D cell 3V lighting--Both are frame (chassis) grounded.
The post WWII Kolllsman series of sextants use 28V aircraft power for lighting and are not supplied w/ battery cases. They are supplied w/power cables that plug and securely screw
into recepticles on the sextant and aircraft.