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This topic comprises 2 pages: 1 2
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Author
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Topic: Wenzel Pro 50 restore/rebuild
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John Schulien
Expert Film Handler
Posts: 206
From: Chicago, IL, USA
Registered: Nov 1999
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posted 12-26-2002 01:57 PM
I spent some time on my lamphouse over the weekend. It's a Simplex High 19000 series arc lamp that was long ago converted to use giant DTJ mogul bulbs. Those bulbs are getting tough to find, they are pricy when I can find them and they don't last very long. Besides, the way the socket was installed (basically bolted to the ash pan), I had no way of adjusting it to focus the light spot, and as I received it, the lamphouse put out very, very little light.
Whoever did this hack conversion on the lamphouse removed most of the carbon arc parts in the process. The entire front jaw, arm, and magnet assembly is gone. I had a conversation with a fellow who thought I should restore the lamphouse to use carbons, but there are too many parts missing. Plus, I'm installing this projector in the basement of a 1920s era frame house, which I have no desire to burn to the ground.
The light bulb was the first problem. The second problem was the mirror. The mirror is a back-surface mirror, and the silvering was pitted and flaking. I went through the entire process of stripping away the old silver, cleaning the glass with nitric acid, and re-silvering the mirror. Unfortunately, the problem was that the back glass surface of the mirror is pitted with a crazing pattern, and when I stripped the silver off, I was left with the same crazing pattern in the glass. When I resilvered the mirror, I was left with essentially the same problem as before, except that the flaking problem was fixed.
I found a company that professionally restores mirrors. I got an estimate of about $400.00 to regrind and resilver the mirror. This would bring the mirror to like-new condition. That's over my budget. I just reinstalled the mirror, moved on, and actually, as you'll see, the mirror works nicely, even with the surface damage.
About a year ago I had a bulb burn out in my 16mm projector. I paid too much for a brand new bulb, which promptly burned out a month later. In a fit of pique, I went to ebay and purchased every CTT/DAX bulb I could find, at an average price of about $4.00. I found 20 of them. They seem to be one of the most commonly available projector bulbs. I decided to refit the lamphouse to use these bulbs for two reasons.
First, they are commonly available and turn up as surplus regularly.
Second, unlike the mogul bulbs, these bulbs have an internal back reflector. The mogul bulbs cast light out in all directions. Only the light rays heading in the direction of the mirror (and the negligable amount of light that travels straight from the filament to the gate) are put to use illuminating the film. This means that over half of the light is wasted. I positioned the light bulb facing backwards, towards the mirror, so the light that would otherwise be wasted (by illuminating the inside front of the lamphouse) is instead reflected back into the mirror. In practice, using the bulb with an internal reflector in place of the mogul bulb nearly doubled the light output from the lamphouse.
I wanted to be able to adjust the bulb position in all directions -- forward and back, up and down. Left/right wasn't such a concern -- I just wanted to get that right the first time. I also wanted to minimize the profile of my mechanism so that it wouldn't block too much of the light coming back from the mirror.
I took advantage of the one part of the original carbon arc mechanism left in the cabinet -- the forward travel arm. I cut a piece of hollow bar stock, and drilled three holes in it. One to attach it to the travel arm, the other two to attach the socket. I purchased a new CTT/DAX style socket from Bulb Direct, and mounted it to a small rectangle of aluminum. I drilled holes in the aluminum plate to match the holes in the hollow bar stock, and created an adjustable riser using two bolts and stiff springs.
Here is a picture showing the entire assembly, and the state of the mirror as well. The lamphouse is running at low power on a variac for this picture. If you look inside the bulb, you can see the reflector.
I can adjust the filament height with the bolts and springs. I can adjust the filament distance from the mirror using the travel arm control on the back of the lamphouse.
Once I had assembled everything, I tested it by positioning a piece of white board at the aperture distance, and started adjusting things to make the spot as small as possible. I was able to focus the light beam down to about a two inch spot. I know that I'm not achieving the full potential of this lamphouse, because the lamphouse was originally designed to focus a spot of light, not a grid of light.
In this case, the sweet smell of success was burning paper. Yep. the piece of paper I was focusing the beam on caught fire. That's when I was pretty sure that things were going to work out. As things stand, the lamphouse puts out enough light to nicely light a six foot screen, which is exactly what I was trying to do.
Here's an image showing how the light cone converges on the projector fire shutter. The lamphouse is running at low power on a variac. Notice how little stray light there is in the front half of the lamphouse.
Once I resolve my intermittent problems, it will be time to move on to the sound. I have the original amplifier, but it's battered and in poor shape. I suspect I'll be rebuilding it completely.
My test reel is an odd reel from a foreign film with subtitles, so it's been actually quite enjoyable to make the adjustments, and see everything work so far. I have the shutter adjusted so there is no travel ghost, and the picture is completely steady.
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