On 2012-10-12, Michael A. Terrell wrote:

The projector bulbs in the old RCA TP66 film chain were mounted in a
vertical line. If you used the bottom lamp, and let it switch the to
spare on top, they had a short life of a little over 20 hours. If you
ran the top lamp, with the spare at the bottom, the life was over five
times longer. The projector used a motorized track, with a relay in
series with the filament. When the filament opened, the relay dropped
out and turned on the motor. In either position, it would run to look
for the other bulb when the one in use failed. I would pull the bad
lamp and move the good lamp to the top at the next film change, then put
the new lamp in the bottom socket. I averaged over 130 hours per lamp,
that way.

Are you saying that 20 hours resting above the working lamp knocked 100
hours off the lifeime? in other words, I
f you did the opposite did that reduce the
life of every lamp to 20 hours.

Or was it 130 hours above the working lamp that reduced the life of
the spare by 100 hours?

It seems surprising that the lamps were so readily damaged by
environmental heat


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