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Other Vintage Household Electrical or Electromechanical Items For discussions about other vintage (over 25 years old) electrical and electromechanical household items. See the sticky thread for details.

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Old 23rd Feb 2024, 2:11 am   #21
broadgage
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Default Re: Cabin Slide Projector

I would suggest a modern halogen headlight bulb with an improvised mounting in order that it may adjusted for optimum position.
These are made by the million and therefore very affordable.
12 volt, 55 watt is probably the most common rating.
Ideally run it at 14 volts as that is the voltage in a vehicle with the engine running and the battery on float charge.

These lamps are robust and generally last several years use exposed to vibration.
I would expect the screen illumination to be better than with the original mains voltage 100 watt lamp.
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Old 19th Mar 2024, 4:23 pm   #22
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Default Re: Cabin Slide Projector

Quote:
Originally Posted by broadgage View Post
I would suggest a modern halogen headlight bulb with an improvised mounting in order that it may adjusted for optimum position.
Can you provide further details e.g. what type of mounting - thanks?
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Old 20th Mar 2024, 9:29 am   #23
broadgage
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Default Re: Cabin Slide Projector

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Quote:
Originally Posted by broadgage View Post
I would suggest a modern halogen headlight bulb with an improvised mounting in order that it may adjusted for optimum position.
Can you provide further details e.g. what type of mounting - thanks?
Depends a bit on circumstances, but I would mount the lamp holder on a length of "all thread" in order that the height may be adjusted.
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Old 22nd Apr 2024, 3:33 pm   #24
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Default Re: Cabin Slide Projector

My ongoing search for a replacement cheap and cheerful ‘sacrificial bulb’ (240V 100W) just to ensure that my repair work has resolved the arcing issues in the lamp base has been in vain!

Not sure what I can do unless anyone knows a source for NOS bulbs?
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Old 22nd Apr 2024, 8:45 pm   #25
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Default Re: Cabin Slide Projector

Hi, if you are looking for a " Test " lamp. how about a standard car indicator bulb, same base 12v 21w. running it on 12v supply although the voltage is lower the current drawn will be higher, so may indicate the success of your repair.
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Old 23rd Apr 2024, 4:48 pm   #26
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Default Re: Cabin Slide Projector

Quote:
Originally Posted by broadgage View Post
I would suggest a modern halogen headlight bulb with an improvised mounting in order that it may adjusted for optimum position.
These are made by the million and therefore very affordable.
12 volt, 55 watt is probably the most common rating.
.
I would expect the screen illumination to be better than with the original mains voltage 100 watt lamp.
Why are low voltage incandescent lamps more efficient at a given wattage than mains voltage ones? Is it because their filaments are thicker and stouter and this permits them to be run at a higher operating temperature - thus they give out more light versus heat?

Steve
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Old Yesterday, 5:17 pm   #27
DonaldStott
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Default Re: Cabin Slide Projector

Quote:
Originally Posted by seymour32 View Post
Hi, if you are looking for a " Test " lamp. how about a standard car indicator bulb, same base 12v 21w. running it on 12v supply although the voltage is lower the current drawn will be higher, so may indicate the success of your repair.

I've tried a 12V 21W car bulb running from my bench power supply and all seems well, no arcing, very bright - no idea how the repaired base will bear up at 240V 100W?
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Old Yesterday, 7:06 pm   #28
Brigham
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Default Re: Cabin Slide Projector

I would think that if the repair can take almost two amps at 12 volts, it will be able to take less than half-an-amp at the higher voltage.
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Old Yesterday, 7:41 pm   #29
DonaldStott
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Default Re: Cabin Slide Projector

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Originally Posted by Brigham View Post
I would think that if the repair can take almost two amps at 12 volts, it will be able to take less than half-an-amp at the higher voltage.
Point taken - good old Ohm's Law says 0.416A.
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Old Yesterday, 10:03 pm   #30
emeritus
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Default Re: Cabin Slide Projector

The lower voltage bulb will indeed have a shorter and thicker filament. The consequence is that, for a given wattage, the lower the voltage, the higher the light output.

In the case of bulbs for projectors, a secondary effect is that the more compact low voltage filament can be a closer approximation to a point source, allowing the optical system to make better use of the light.
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Old Today, 8:37 am   #31
seymour32
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Default Re: Cabin Slide Projector

personally I would very wary about converting to a halogen lamp, as they run a lot hotter due to the "halogen cycle"( over 250 deg C). The original 100w lamp around 130 deg C. All the projectors I have come across with halogen lamps have fans to cool the film/slide gate. There are some bulbs around on auction sites but at a hefty price and not all in the UK.
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Old Today, 12:05 pm   #32
Panrock
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Default Re: Cabin Slide Projector

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The lower voltage bulb will indeed have a shorter and thicker filament. The consequence is that, for a given wattage, the lower the voltage, the higher the light output.
I'd like to be pedantic and try and pin this down, if I may. By the "higher" the light output, do you mean the more "intense" the light source? If so, I'd agree. But surely the total light output would remain the same irrespective of voltage, and be determined solely by wattage and filament temperature (which admittedly could increase due to the greater intensity).

Quote:
Originally Posted by emeritus View Post
In the case of bulbs for projectors, a secondary effect is that the more compact low voltage filament can be a closer approximation to a point source, allowing the optical system to make better use of the light.
Indeed.

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Old Today, 12:51 pm   #33
vidjoman
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Default Re: Cabin Slide Projector

Although I’ve not seen a picture of the bulb I suspect that it’s a tubular glass and the filament is a coiled coil that’s a length fitted to 2 glass strips, one at the top and one at the bottom with the filament going up and down to form a flattened light source. This type was common way back before we got lamps with built in reflectors. There will be a reflector behind to make most of the light shine forward.
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