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Author
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Topic: Lamp life
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Michael Dixon
Junior
Posts: 29
From: East Bend, NC, USA
Registered: Nov 2009
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posted November 28, 2009 07:55 AM
Apologies if this is an already overworked topic. My Sears 3.9288 std.8 projector, purchased new in 1963, has never required any repair and still runs very well. The DLS lamp is not low cost. One online USA source has the price over $120.00 each, but other sources are available at lower cost. 30 or more years ago, a magazine article showed how to use a double-throw switch and a thermistor to gradually warm up the lamp before going to full voltage/brightness. I made this modification to this projector with good results. I do not recall the exact thermistor used. As most already know, an incandescent lamp has very low resistance when cold. The immediate current (amperage) inrush when energized is considerably greater than the normal operating current and is brutal to the lamp filament. Burnouts often occur at startup. The thermistor, via the switch, is in series with the lamp and a thermistor is very high resistance when cold. Once the lamp is lighted, the switch is thrown to the other position and the lamp assumes full brightness. My Eumig projector, presently not in operating condition, instructions seem to indicate that some sort of lamp pre-warming system is standard on the Eumig.
On a somewhat related matter, lamp substitution charts are available at http://lms.jefferson.k12.ky.us/lamp.html. They have a second page of listing that I could access only by another Google search. Some of these lamps are used in motion picture projectors.
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Paul Adsett
Film God
Posts: 5003
From: USA
Registered: Jun 2003
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posted November 28, 2009 08:47 AM
Michael,
You are absolutely correct, pre-heating of the lamp filament is essential to get good lamp life. On the Eumig and Elmo projectors the lamp gets about 3 volts applied as soon as you switch the projector on (or in the case of the Eumig 800 series, as soon as you plug it into the wall socket). This low voltage produces a dull red glow on the filament, which as you say, reduces the 'shock' to the filament when the full voltage is applied.
I am not familiar with your Sears projector, but $120.00 for a lamp is incredibly expensive. Most super 8mm lamps cost about $15.00 -$30.00.
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The best of all worlds- 8mm, super 8mm, 9.5mm, and HD Digital Projection,
Elmo GS1200 f1.0 2-blade
Eumig S938 Stereo f1.0 Ektar
Panasonic PT-AE4000U digital pj
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