Re: Allan Woods-Projection lamps? ( digest 1585)

[P3D Bob Howard <bobh@xxxxxxxxxxxxxxxxxxxx>]

RE: Allan asks why all the varities and how would you choose?

Allan..the varities exist because of history..to fit all the projectors
past and present. In the beginning toy projectors used even frosted lamp
as you used in home lampstand. But good projectors are especially motion
picture projectors had to get a lot of light at the gate, so this needed
large wattage lamps with concentrated filaments that could be focused by
condeser system. These evolved (for 110-130v lamps) into the T-10 and
T-12 (meaning tubular and diam in 1/8th inch..so T-12 is 1-inch across).
These except for the B&H tanged lamp, had a bayonet socket to be sure
the filament was in a prefocused position. (The B&H base was so you had
to buy their initially). These lamps had a cc-13d filament. CC meaning
coiled coil..to concentrate the turns of tungsten wire. and these
'coils" arranged in a square pattern of 7 and 6 coils, one set filling
the gaps of the other. This made a high intensity grid that was the
light source. Life about 25 or 50 hours. Smaller projectors often used
a bayonet base like auto lamps or flashbulbs in a globular buld and with
a tight cc filament much like the headlamp filament.
With the advent of halogen lamps and quartz bulbs. (Halogen refering to
the gas to inhibit tungsten evaporation..and quartz to withstand heat
and make a bulb smaller and much nearer the filament)it wsa possible to
mount these bulbs in little reflector with prefocused base design to
match projector lampshouse designed for them. Used too in the color
enlarger heads that flood a filtered mixing box with light. So these
bulbs are the ones to chooose unless you are looking for a replacement
for an old projector. In the late forties, you had to order a bulb by
specifiying the base, bulb shape, and filament besides wattage and
voltage design. While on ASA committee. I suggested that since you could
buy a radio tube as a 6J6 without a lot of description, why don't we
catalog lamps that way. And they soon did. BobH
(So you may find a lamp shown as a KEH I just made up those letters.)


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