Miniture 12v bulb types ??? military aircraft instrument 'p' lights?

Question

i need to change the bulb in a dashboard 'p' light i'm using, to a higher wattage but i can't find who make them, or what size they are! They were original used on aircraft instrument boards to light the gauges and switches and consist of a small post aprox 10mm diam x 25mm high with a small window slot cut into the top with a red lens in to produce a red glow across the surface there mounted on. the bulb is 6mm in diam and 15mm long with smooth sides and a single terminal on the base, therefor earthing through the metal body of the post.

Anyone have any idea what these bulb types are called or who make them?

Answer 1

I had a look in the Maplin catalogue.

I think the bulb you describe is Order No BT51F.

They only have this one, 28v 40mA  (Therefore 1.1W).

28v is right for avionics kit.

Answer 2

If you remove the bulb from the post you should find a number stamped on it. Most of these bulbs were made to a military standard and even commercial bulbs still use them. The number will help you find the size and rating of the bulb. They are made by many manufacturers like GE, Micro Lamp, Gilway, Chicago Miniature Lamp, etc.

Unlike bulbs for your house lamp, you won't find that these are 60W or 100W varieties. They are rated by voltage, current, MSCP (mean spherical candle power, i.e. how bright they are) and life (how many hours they are designed to operate).

I believe that many of these types of light posts used T-1 3/4 flange based subminiature lamps. If you have a 12V or 14V system, the bulb may have the number "330" stamped on the side. This was the most common 14V lamp of this type, and also the brightest. Other possible lamps of that size and voltage range would be 382, 394, and 8918.

If you want brighter bulbs you will need to find a totally different type of lamp or use more than one of these lamps. These small lamps were not designed to be very bright, and most aircraft used at least two of them to light a single instrument.

Answer 3

Doesn't ring a bell but have a look through these:-

http://cpc.farnell.com/jsp/search/result...