[Milsurplus] Arc Lamps for projector sets

[J. Forster]

On the topic of carbon arc lamps, I believe it is easier to make an arc
lamp to run on DC than AC.

The DC electrodes are different, positive and negatice. The AC electrodes
are the same for both.

I think movie projectors use DC to avoid strobing effects, because the
projector has a shutter that is closed while the film advances. In the US
that is 24 per second, and has common factors w/ 60 Hz.

Even using filtered DC there is some strobing and the projector has a
mechanical differential to adjust the shutter phase.

-John

====-



> Way back, when I was still in high school, I worked in
> a theater which used carbon arc lamps but we had
> a motor generator which provided the DC for the arc lamps.
>
> I am almost positive the lamps were made by Peerless and
> very similar to:
>
> http://www.flickr.com/photos/combatcamera44/6103931423/in/photostream/
>
> 73
> Sheldon
>
> On 4/30/2012 5:57 PM, Richard Solomon wrote:
>> Most of the Movie Theatres in Downtown Boston used DC for the Arc Supply
>> on
>> their projectors. Copper coated Carbon rods were used.
>>
>> BTW, anyone remember the War Surplus store next to the old Radio Shack
>> on
>> Washington Street ? Just outside Scollay Square.
>>
>> 73, Dick, W1KSZ
>>
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