||This MA lamp represents one of the earliest styles, with production of discharge lamps having commenced barely ten years earlier. It employs a crude arc tube frame mount and the style of the packaging is a type which was phased out before 1950. The date code of 25 can therefore be translated into its manufacture date being January of 1944.
To make the MA lamp sufficiently efficient to be commercially viable, a glass having a very high softening temperature was required, and the aluminosilicate glasses were developed by the lamp industry specifically for this application. This lamp employs BTH's Chesterfield C14 grade which was the first of the aluminosilicate glasses. Its softening temperature is marginally lower than for later glasses, hence the rated life of this early lamp is quite short. It delivers 18,000 lumens and the lifetime is 3,000 hours. Later lamps had improved glasses and life was trebled with only marginal loss of efficacy.
The arc tube here is fabricated from a blown bulb, originally dome sealed at one end and having a constriction just before the open end. The main electrodes are supported on a moly t-piece, one of which was hand sealed into the dome end along with an auxiliary starting electrode and the exhaust tubulation. A second electrode was then sealed into the constriction at the open end and the cullet glass removed. To minimise thermal losses, both ends of the arc tube have been coated with a heat-reflective platinum paint. Electrodes take the form of a thoria pellet double-wound inside a tungsten coil. It is interesting to note the lamp voltage, 148V written on the stem in indian ink. The screw cap has been lubricated with graphite for easy replacement.