Vintage McAlister Fresnel Mod (pics)

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ostrograd
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Vintage McAlister Fresnel Mod (pics)

I've had an old 1K movie light sitting around for awhile, probably from the 1960s. It still worked, though with a 750W lamp in it was way too bright for around-the-house use, not to mention some serious heat generation. You can find these on Etsy converted to a standard E26 screw base so you can stick a regular household bulb in there, but doing that seemed a bit boring, like neutering the light in some way. I figured it'd be a fun project to convert it to LED while making only minimal changes to the fixture itself. I wanted to turn it into a nice decorative light, one bright enough to use a reading or task light, but not overpowering. Here's what I came up with.

Parts list:

  • 8 x Nichia Optisolis 3500k
  • 2 x Virence VR21P4 MCPCB
  • 5 x copper penny
  • Philips 750W 120V EGR lamp (existing)
  • LuxDrive BuckPuck 700mA LED Driver
  • TRACO Power 15W 12V 1250mA Encapsulated AC/DC Power Module

The original lamp looked like this:

750W EGR lamp

My plan was to cut it open, take out the filament, and replace it with a 2-sided LED module. Then I could use all the existing wiring in the fixture, just step it down from 120V AC and add a driver somewhere in the middle, since I wanted to keep the original beefy electrical cord and switch. A 2-sided LED module because the original lamp is omnidirectional so the fixture has a parabolic reflector sitting behind it to reflect some of that light back out the front. Not the most efficient setup, but might as well duplicate it as closely as possible for authenticity's sake.

 

Lamp mod, side view

The heatsink is 5 copper pennies bonded together with Arctic Silver. The middle one I filed down on the sides and bottom, then drilled a few holes in various places to allow the two MCPCBs to be wired in series. Then bring the power up the same way it came in the original lamp.

So it pops into the fixture same as always.

modded and mounted lamp

modded lamp from above

Now the only thing left was to rewire things a bit so I had the proper voltage and current being sent to the lamp base. Fortunately I found a very compact AC/DC transformer and since the rear spot/flood adjustment lever had gotten broken off years ago, there was a natural spot to stick the transformer and the driver. Much better than having a manly light like this plugged in via some wimpy wall wart Smile

This is inside the back of the fixture, looking down.

power supply

Plug it in, flip the switch, and it works. Not super bright, but good enough for its new role as a decorative light fixture, once I find a vintage stand for it. Makes a fun reading light. The beam profile is nothing to write home about, but it's passable, and the spot/flood adjustment works fine.

And you have to admit, this fixture is a sweet bit of industrial design, all around.

Edited by: ostrograd on 09/21/2019 - 22:32
Lightbringer
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Hjeh, nice bit of nostalgia, I gotta say. LOL

Any fan in there or anything to cool down the LEDs? The pennies would provide thermal mass, but heat’s still bottled up with an air-insulator keeping it in place.

Figure 2W per LED, times 8 LEDs, is 16W cooking them in-place. Be careful. Shocked

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

ostrograd
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Thanks for looking!
It should only be one quarter of that, right? Typical Vf of those LEDs is 2.8V, then on each board they’re wired in parallel, so that’s 175mA per LED. Meaning 1/2W per LED, and 4W total. It does get rather hot though, so you’re probably right. I’ll measure it with a thermometer Monday, but tonight’s very subjective measurement is that touching the heatsink doesn’t result in an immediate burn, though I wouldn’t enjoy holding my finger on it for too long either.
The fixture itself has plenty of ventilation, but there’s no active cooling going on for sure.

Tweakmeister
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Very cool thanks for sharing!

Lightbringer
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ostrograd wrote:
It should only be one quarter of that, right? Typical Vf of those LEDs is 2.8V, then on each board they’re wired in parallel, so that’s 175mA per LED. Meaning 1/2W per LED, and 4W total. It does get rather hot though, so you’re probably right. I’ll measure it with a thermometer Monday, but tonight’s very subjective measurement is that touching the heatsink doesn’t result in an immediate burn, though I wouldn’t enjoy holding my finger on it for too long either.

Ah, that’s the key, then. When you mentioned they were wired in series, I thought (powered from mains) that they were all wired in series, 4+4.

ostrograd wrote:
The fixture itself has plenty of ventilation, but there’s no active cooling going on for sure.

Heat should be pretty manageable, then.

Sounds like a fun project. LOL

09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0

Cereal_killer
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Wow that things cool!
How did you manage to cut a hotwire bulb cleanly without it exploding?

 RIP  SPC Joey Riley, KIA 11/24/14. Now I am become death, the destroyer of worlds.

Lexel
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that thing with some sort of mini water cooling would be great to drive more powerful LED

ostrograd
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Lightbringer wrote:
Ah, that's the key, then. When you mentioned they were wired in series, I thought (powered from mains) that they were *all* wired in series, 4+4.

Sorry, what I should have said was, the boards are wired in series, but then on each board the LEDs are in parallel. Like this, if you'll indulge me some ASCII art:

   |
  / \
/ | | \
X X X X
\ | | /
  \ /
   |
   |
  / \
/ | | \
X X X X
\ | | /
  \ /
   |

Cereal_Killer wrote:
How did you manage to cut a hotwire bulb cleanly without it exploding?

I was worried about that, but it turned out not to be hard. I used a tile saw—the water-cooled kind—with a toothless diamond blade for cutting glass (Bosch DB769). If you go slowly it makes a nice clean cut.

Lexel wrote:
that thing with some sort of mini water cooling would be great to drive more powerful LED

Yeah, after I'd ordered the parts Clemence came out with a 36-LED board that's not a whole lot bigger. I may try a second version with that sometime. It would indeed be sweet. With a better heatsink of course Smile

Marc E
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That is niiiice Smile