Film-Tech Forum ARCHIVE: Help me fix a 1940's spotlight.

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Posted by Michael Rourke (Member # 1142) on 04-20-2002, 10:43 PM:

One thing I have been itching to get working since I have started working at the Fremont is the Motion Picture Accessories Co. spotlight and color wheel circa 1940.

The bulb had gone out long ago and it is the weirdest looking thing I have ever seen, I have little hope of finding a replacement, but here is the info anyway: GE Globe type bulb, (large) 2 pin base, 3200 degrees Kelvin, 120V 2MIG48/18. The bottom says K KBO 74, it's 9 inches in length and 18 inches around at it's largest point. The filament would be best described as a "ladder" consisting of four seperate elements (rungs). I have NO IDEA what the wattage of the bulb is so that puts a damper on things.

I emailed several bulb sites that claimed to have obsolete bulbs but I got a lot of head scratching.

Also, there is a receptacle in the back of the spot that you plug a cord into and then into a wall outlet, the receptacle has one vertical hole and one horizontal??? Is this 220V? The receptacle then leads 2 sets of 2 wires, white and black, the white go to the bulb socket, and the black go to the motor to turn the color wheel. If the plug is 220V why is the bulb 120V? The cord for the spotlight is long gone and there aren't any similar outlets in the booth.

Someone suggested converting it to Xenon, but it's so simple right now..couldn't I take out the bulb socket and replace it with a newer one and run AC? That makes more sense to me.

Of course, if any of you wonderful people know where I can get the original type of bulb, or have any info on the company Motion Picture Accessories Co. that would make things much easier.

Thanks, just for reading this crap.

Posted by Stan Gunn (Member # 554) on 04-20-2002, 11:30 PM:

I would be inclined to fit a more available lamp. Maybe around 2kw
I think would do, from the sound of it the effort would be worth it.

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Posted by John Anastasio (Member # 607) on 04-21-2002, 08:57 AM:

The socket was built that way for safety reasons. You couldn't use anything but the cord that came with the lamp...so you wouldn't have someone trying the run a 2K lamp with an old extension cord. I'd just wire a new cable directly to it. Get a heavy duty 20 amp appliance cord from Lowes or Home Depot. That way you can ground the metal case as well. You might have to use heat-resistant bronze wiring on the interior, depending on how hot it gets inside. It's available from theatrical supply houses. 2-pin lamps are easy to find. I've got sixteen Rank 2K Fresnels in my studio that use them. The new lamps are much smaller and much more efficient. The only problem I can foresee is that the filament may be in a different spot, leading to a focus problem.

Posted by Bill Carter (Member # 156) on 04-21-2002, 12:05 PM:

Try calling Mole-Richardson in Hollywood, at (323) 851-0111. They might be of help in identifying and finding the right bulb. That type of bulb tends to be common in studio lighting instruments, and there are quite a few "2-pin" incandescent types still in fairly common use.

Posted by Bob Peticolas (Member # 328) on 04-21-2002, 12:40 PM:

Michael,

That plug on the spotlight is 120V, 20 amp. Normal household outlets have two parallel sockets for 15 amp circuits. Commercial outlets sometimes are wired for 20 amps and will have a straight slot and a "T" shaped slot. Then when you have a device that requires 20 amps, the plug will have the pattern you described to prevent it being plugged into a less than 20 amp circuit.

A contractors supply store (or even Home Depot or Loews) should have a 20 amp power cord that you could use with the right ends. But, I would aggree with changing the plug out to a modern 3-wire to get the grounding protection.

It sounds like it was a 2kw lamp. Putting a modern quartz bi-pin replacement in should work fine, but you may have to modify the location of the mounting to get it to focus right.

Good luck,

Bob

Posted by Gordon McLeod (Member # 33) on 04-21-2002, 12:56 PM:

Most modern quartz lamps have a single coiled filement in them not a planar type that most of the older fixtures were designed around
Don't be suprsed if it doesn't focus all that well
gordon

Posted by Michael Rourke (Member # 1142) on 04-21-2002, 04:12 PM:

Sorry, there might be some confusion.

The bulb is not a tube like for a halogen worklight, it's a globe with 2 pins at the base.

I wonder if you guys are picturing a box spot with the folding flaps on it? This spot looks more like a carbon arc lamphouse with a decorated plate just after the lens and a motorized color wheel in front of that plate.

The bulb fits in the socket and the circular reflector then screws onto the socket just behind the bulb.

Oh, if only I had a digital camera! Suffice to say this thing is really cool and there is a guy in Arroyo Grande that RUNS the same thing and the SOB doesn't even know where to get the bulbs because he's never had to change it! They don't make 'em like that anymore.

Posted by Gordon McLeod (Member # 33) on 04-21-2002, 05:23 PM:

Two big pins on the base are usually called mogual bipost
If it has a large round globe then it would be a "g" serries lamp
Again the problem of retrofiting a different lamp is the optics usaly have a problem evenly gathering the light from the small coiled filament of modern quartz lamps
A xenon would probably also have a problem as well as it is so compact
A possibility would be a HMI or CSI lamp
they have a large plasma discharge and can be run using a choe type ballast
Thorn used to make a range of 1K CSI and CID lamps and ballasts

Posted by Steve Kraus (Member # 476) on 04-21-2002, 11:31 PM:

It's possible that the large globe bulb is no longer available but a direct halogen (quartz idode / tungsten halogen, whichever term you prefer) replacement is. This would be a small bulb mounted on a ridiculously large base that matches that of the old style bulb.

Gordon: Doesn't it become easier to gather light from something approaching a point source? For example, consider how little use low pressure sodium has compared to high pressure sodium despite the former's significantly higher raw efficency. Much more awkward to design good reflectors for their large envelopes.

Perhaps the problem will be that the light is focused *too* well, producing a hot spot and will need to be defocused.

Posted by Michael Rourke (Member # 1142) on 04-22-2002, 12:29 PM:

Well, I think I will replace the socket, rewire the plug and run an HTI bulb.

Of course if they decide to put a slide projector in this screen it will make all my effort for not. I know slide projectors have their place in our business because of the revenue they produce, but on the 40's house with the neon ceiling and murials all over the walls I don't think people will appreciate it. I was hoping to play Jump Swing on the Non-Sync, and run the spot/color wheel between shows to add to the ambiance, but MovieTunes and NCN slides will have to do.

Posted by Gordon McLeod (Member # 33) on 04-22-2002, 04:37 PM:

Most of the reflectors were faceted to reflected and condense the large panar filament