Cabin Slide Projector

[broadgage]

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.

[DonaldStott]

Originally Posted by broadgage

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?

[broadgage]

Originally Posted by DonaldStott

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.

[DonaldStott]

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?

[seymour32]

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.

[Panrock]

Originally Posted by broadgage

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

[DonaldStott]

Originally Posted by seymour32

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?

[Brigham]

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.

[DonaldStott]

Originally Posted by Brigham

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.

[emeritus]

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.

[seymour32]

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.

[Panrock]

Originally Posted by emeritus

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).

Originally Posted by emeritus

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.

Steve

[vidjoman]

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.

[David G4EBT]

Would this fit the bill:

https://www.lampco.co.uk/products/ba...IaAkF8EALw_wcB

'BEE Single envelope JD Ba15d 240V 100W Clear 1100lm 1500h 15x75mm High voltage halogen lamp'.

(£10.79 + £3.96 P&P Vat inclusive).

[G6Tanuki]

Having beenm following this thread with interest, can someone tell me just what a "Cabin Slide Projector" would have been used for?

Was it something used to project slides of maps onto a display for marine navigation pilots or their aircraft-equivalents to view? Or was it something used for entertainment purposes on board yachts?

Inquiring Minds Want to Know!

[emeritus]

Somewhere in the shed I have a circa 1930 General Electric (USA) lighting course manual which explains why lower voltage lamps of the same wattage produce a greater light output than higher voltage ones. It has tabulated data for, I think, 240V, 120V and 50V lamps. I'll see if I can dig it out and post a scan.

[DonaldStott]

Originally Posted by David G4EBT

Would this fit the bill:

https://www.lampco.co.uk/products/ba...IaAkF8EALw_wcB

'BEE Single envelope JD Ba15d 240V 100W Clear 1100lm 1500h 15x75mm High voltage halogen lamp'.

(£10.79 + £3.96 P&P Vat inclusive).

Thanks David but unfortunately this bulb has two contacts on the base whereas I need the older type with only a single contact.

[DonaldStott]

Originally Posted by vidjoman

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.

I've attached a picture of the bulb in question - note the reflector at the top:-

[wd40addict]

https://www.ebay.co.uk/itm/373949194610

[seymour32]

Can the bulb base not be re soldered? or has filament failed ?