Slide Projectors -- General Questions about upgradability

[DrTebi]

Hello,

I am planning on upgrading a slide projector. It's a Beseler Slide King, which I obtained quite cheap. It works OK, but I believe I can upgrade it to make it much better.

-- Slide Holders --
I think I already figured this out... the original holders were made for larger slides (or plates?), but it was quite easy to attach some masks and spacers to make 6x7 Slides fit very nicely.

-- Lens --
I happen to have a Schneider Kreuznach 250mm f/4.0 lens which was made for a 6x7 projector. It doesn't fit the way it is, but I experimented a bit by removing the projector's bellows and setting it into place temporarily, and, apart from the fact that the image is a bit too small for my room/screen, it works perfectly. I will need to figure out a way to mount it properly, and make new bellows. Any advice would be appreciated.

-- Light Bulb --
The projector came with a 500 W light bulb, which I found a bit surprising, since the projector is rated for 750 Watts, and I have read that some people run it with 1000 W bulbs. These bulbs are still available (new old stock), and I will try a 750 W first. My question is, would it be risky to run it with a 1000 W bulb? As far as I understand, the light bulb runs directly from the mains (aka 120 Volts), so there are no transformer issues. There is however a transformer inside the projector, which I assume is for the fan. This is also the curious thing about it--normally slide projectors have a fan to cool the lamp, but on this projector, according to its position, is seems to be cooling the transformer? Or just blowing hot air out of the case?

-- Cooling --
Since there is plenty of space inside the projector, I am thinking about replacing the original fan with a larger fan with the same CFM or more, in order to get less fan noise but still proper cooling. I am also considering to put a second fan right underneath the slide mounts, which should help to prevent slide buckle with a stronger bulb.

I know I could just leave it as it is... but I think there is quite some potential to make it better, and I like the challenge.

I would appreciate any comments regarding my ideas, or even further upgrade suggestions.

 

[AgX]

-- Light Bulb --
The projector came with a 500 W light bulb, which I found a bit surprising, since the projector is rated for 750 Watts, and I have read that some people run it with 1000 W bulbs. My question is, would it be risky to run it with a 1000 W bulb? As far as I understand, the light bulb runs directly from the mains (aka 120 Volts), so there are no transformer issues.

It may be that the addiditional current is above the rating of the wiring or the lamp fixture.
It may be that added convected or radiated heat of the lamp is more than the slide or the lens can take.

 

[AgX]

There is however a transformer inside the projector, which I assume is for the fan. This is also the curious thing about it--normally slide projectors have a fan to cool the lamp, but on this projector, according to its position, is seems to be cooling the transformer? Or just blowing hot air out of the case?

I can't imagine a transformer to be cooled.

Furthermore low voltage fans should be rare with appliances of that era.

Maybe you mixed up the (mains) fan motor with a transformer?

 

[DrTebi]

Thank you for replying.

I took a closer look, and I did mixup the fan motor with the (non-existing) transformer.
The fan is a centrifugal fan, and it actually sucks air in from the bottom, and blows it towards the light bulb. Air can escape through perforations on the top of the projector. So that makes perfect sense now. I have found a few centrifugal blowers that would fit from YS Tech, these run on 12 or 24 Volt DC though. I couldn't find anything suitable (around 120mm square) in 120 Volts. So I assume I will have to add a small transformer (the fans only need about 1.1 amps). The trouble however is, that I don't know the airflow (CFM) of the existing blower. If I put one in that has less, it would obviously be of no advantage... I will try to take it out and look for specs on the fan.

Regarding the voltage, I haven't thought about the rating for the lamp fixture. I will have to check that, and maybe replace the fixture if necessary. I have checked the slides after longer exposure, and they were hardly warm, so I think the current air flow is very efficient. The distance between the bulb and slide is quite a bit, too, which helps.

Attached a couple of photos of the Slide King. Inside you can see the condenser assembly on the left, in the center the light bulb, and on the right the motor/fan blower. I have already removed the bellows and lens.

 

[ac12]

In general, I would NOT go above the rated wattage of the unit. Especially with a device that is OLD, since you don't know what components have deteriorated, and to what degree. You may need to replace all the electricals, which may or may not be easy to source. And make sure that all the components and wires are rated for the current (10 amps for the 1,000w bulb) + a safety buffer (so maybe 15 amps). If you do not need the additional light from the 750w bulb, using a 500w bulb will be easier on your slides, and the projector itself, with less heat generated.

 

[DrTebi]

Thank you for your advice, ac12.

I am planning on replacing all electrical components. There really aren't that many--the mains connector, the wires, the switch, and the bulb socket. I have already found a bulb socket rated for 10 amps, I think the other components will be fairly easy to source.

Last night I talked to my father for a while, who has been filming and projecting his films all his life. His advice was to use a digital thermometer with a probe to test what the current temperature is during operation, and then test it with a 750 W bulb. That way I can make a decision on how much more cooling I will need. He also recommended to add a grounding wire to the unit, and definitely replace the wires, mains socket and switch; the wires are of the very old type (some type of fabric insulation).

By the way, do light bulbs loose "lighting power" over time? In other words, if I replace the 500 W bulb with a new 500 W bulb, can I expect more light output, or is this only the case for non-incandescent bulbs?

 

[AgX]

Standard incandescant lamps loose light emission due to vapourisation of the metal and condensation at the bulb. One may argue on the effect of this.

Furthermore the colour temperature will rise with the thinning of the filament.

 

[DrTebi]

The first couple of upgrades are done, see attached images.

I bought a new switch, it is, just like the old one, simply a light switch like one that is used for ceiling lamps etc. It's rated 15 Amps at 120 Volts. It was really easy to install, since it has the same thread holes etc. as the old one.

I also installed a new mains socket. This one is rated 10 Amps at 250 Volts. It also includes a ground connection, which I will simply attach to the metal case of the projector. The socket was a bit more work to install, since it is smaller than the original. I opted to cut a little bronze plate to size, so that the original hole would be covered. Everything is properly mounted with screws and nuts.

I haven't done the wiring yet, I will wait for the new light bulb socket. I did however take pretty much everything apart. Most of the wires were in pretty bad shape, except those of the fan, maybe the fan had been replaced at some point. When I got to the bulb socket, I was able to see its rating--it's rated for 1000 W. The original switch and mains socket were rated for 10 Amps, so the only reason I can think of why the projector was not "officially" rated for 1000 Watts on the plate is, that the blower is not made for 1000 Watt light bulbs.

By the way--when I looked for light bulbs, I also found a Halogen light bulb with the same bulb socket. Is there anything that should stop me from trying one? It's rated 500 Watts, 200 hours and has 10000 Lumen... that would be awesome. But I am not sure how much more heat a halogen bulb produces as opposed to one of the original light bulbs.

 

[AgX]

By the way--when I looked for light bulbs, I also found a Halogen light bulb with the same bulb socket. Is there anything that should stop me from trying one? It's rated 500 Watts, 200 hours and has 10000 Lumen... that would be awesome. But I am not sure how much more heat a halogen bulb produces as opposed to one of the original light bulbs.

Yes, the optics.

Your current system should be optimized for the lamp installed. Any other position of the filament, or even the filament size may alter the illumination.

So far the theory...

 

[DrTebi]

So you mean that the "point of light" would be different, and would then not correctly be enlarged by the condenser? The vertical/horizontal position of the filament could be changed without too much effort.

What about heat... do they run hotter than incandescent bulbs?

 

[AgX]

Yes, the filament temperature is much higher, and thus the colour temperature too.

The basic idea behind behind halogen lamps was to enable incandescent lamps to run at higher temperature than feasible so far.

The infrared fraction of the emitted light though is smaller than with standard lamps, but that would be beaten by the higher light output. So the absolute IR Radiation would still be higher.

 

[David A. Goldfarb]

There were other carriers made for the Slide King, so you may hunt around and see if you can turn one up before adapting the standard lantern-size carrier. If you don't already have mounted 6x7 slides, you could also cut 6x7 mounts for a lantern-size projector.

If 250mm doesn't give you a big enough image for your space, why not look for a wider lens before going to the trouble of adapting it? My shortest lens is also 10", though, and I don't know that Beseler made anything shorter, which may mean that it's not going to be easy to adapt a shorter lens without something like a recessed lens mount, but I haven't tried this.

 

[DrTebi]

Thank you for joining the discussion David

I actually have two original ones for the lantern size slides. I already modified one of the carriers to fit regular 6x7 slide mounts (the GEPE ones). I just added a couple of cardboard spacers, and a thin aluminum strip on each side to prevent the slide from falling forward. It works very well.

The thing about the lens is... the Schneider lens is just so damn good, I don't want to use another one. Compared to the original lens that came with the Beseler, it's much sharper and the image is perfectly evenly illuminated. Götschmann makes a 150mm Schneider lens, which would be perfect, but I will have to save a bit of money for it, it's about $700! But if I would buy that lens one day, I could fit it into the same custom mount that I am planning to make.

Can you share your experience with light bulbs? Which one are you using, did you ever replace the original one?

 

[DrTebi]

Hmmm... there doesn't seem to be much interest in this project, but I will post a conclusive update anyway:

I upgraded all electrical wiring (600 Volt 12 gauge wire), cleaned everything and put it back together. The replacement bulb socket was about 1/2" taller than the original, so I left the original socket, which is rated for 1000 W anyway. I also kept the original wires to the fan, which seemed upgraded already (e.g. proper insulation, no fabric etc.).

I received a 750 Watt bulb, and it worked well. The image was definitely brighter, shadow details came out much better. I did however notice and measure quite high temperatures inside the case (~ 150° C) as well as at the slide (~ 40° C). Leaving a slide projected for more than three minutes did also seem to affect the slide (a slight wavy deformation). The slide itself was still sharp and the color/grain etc. unaffected though.

I then tried a 500 Watt Halogen bulb. The model is a Osram BTL lamp 3050k 500w 120v Halogen Light Bulb (I bought it at Dead Link Removed). This bulb works perfectly, it seems to be intended to be a replacement for the original incandescent bulbs, the filament is exactly the same shape and at the same position. Although it is a bit less bright than the 750 Watt incandescent, it seemed to be the right choice overall. These bulbs have a much longer life time than the incandescent ones, and the color temperature seems more adequate as well.

Temperatures were still a bit high, but I then made some changes to the light bulb housing position. I moved the light bulb housing further back towards the blower, and tried my best to center the filament (I added about 1/16" metal spacers under the light bulb housing mounts to lift it up a bit). The intention was to get a more evenly illuminated image, but it also helped to get the temperature near the slide lower.

Now I get the following temperatures:
@ slide, outside: ~ 25° C
@ slide, inside (at condenser): ~ 33° C
@ inside case, in front of condenser (case closed): ~ 71° C
@ inside case, directly at condenser (case closed): ~ 103° C

These temperatures are all lower than before with the original 500 Watt incandescent bulb. The case gets hot, but can still be touched without burning oneself.

Regarding the lens mount:
I managed to get the lens perfectly centered and pretty tight, by simply adding a strip of mouse-pad, which is about 1/4" thick, between the lens and the original lens mount. Once the lens is in, I can fixate it with the screw (which only presses against the mouse-pad), and the lens doesn't move. Focusing is achieved the same way as before, with the focusing knob.

Overall I must say it was all really worth it. The projector feels a lot more safe now with the new wiring, switch, mains receptacle and additional grounding, it is brighter than before, the image is very sharp and evenly illuminated (see images below).

Although I am quite satisfied for now, I am considering to try a 750 Watt Halogen, and I am also thinking about adding a fan near the slides. The extra brightness really makes a difference in any dark parts of a slide.
Another upgrade I am still missing is some form of bellows, since the Schneider lens doesn't fit inside the original bellows. The projector also strays a lot of light through the top of the case, which can be reflected back with a board at about 30° (it looks silly, but makes a big difference).

If anyone finds this projector, I highly recommend getting it, and performing these fairly simple upgrades. Everything cost only about $35, excluding the Schneider lens. The original lens is OK, the Schneider one is perfect but expensive. Another option might be to try an enlarger lens or a 6x7 medium format lens. It requires a bit of experimentation, but the image will be much sharper with a newer, different lens.

Below a few images with short explanations:

Upgraded wiring, 600 Volt 12 gauge wires with custom-made clips (soldered on):








Image of screen with 750 W bulb, before lamp housing adjustment (notice the uneven illumination):


Image of screen with 500 W Halogen bulb, after lamp housing adjustment (notice the even illumination):


Image of screen, same as above, close-up:

 

[AgX]

A note from the pedantic:

Halogen lamps are incandescent lamps too.


Concerning the heat at the slide stage:

You might consider steering a fraction of the cooling air through that stage. I do not know the construction of your projector and to what extend that would be feasible. In best case a few pieces of bent aluminium plate could work.

 

[DrTebi]

Thank you for the reply. I didn't know halogen bulbs are also considered incandescent. I just read a bit on Wikipedia, that helped to understand the difference... http://en.wikipedia.org/wiki/Halogen_lamp

I just happened to come across a web page overview of Leica projectors (http://www.l-camera-forum.com/leica-wiki.de/index.php/Übersicht_über_die_Dia-Projektoren_ab_1970). There I read, that one projector has a max temperature of 55° at the "Image window", which I suppose is the position where the slide is. Another projector has a max temperature of 65° Celcius.

So I think the temperature I am getting with the 500 W halogen bulb is within an acceptable limit. It would get hotter with a 750 W bulb though...

Currently the air is blown basically from the back of the projector towards the front (a cross-blow fan that sucks air in from the bottom of the case). So technically, it does already reach the front where the slide is. I could add a ramp that directs it better upwards. That is how it's done at the lamp housing, there is a small kind of ramp that directs the air up towards the lamp.

Good idea, I will try to find some metal in the garage that fits...