IMPROVEMENTS FOR THE ELMO GS1200 XENON PROJECTOR DESIGNED BY UGO GRASSI.

Elmo GS1200 Xenon projectors are considered the best Super-8 projectors commercially available, as the far superior Fumeo and Beaulieu models (especially the Fumeo) were always sold in specialist or professional markets. 

Elmo GS1200 Xenon

I have a love/hate relationship with the GS1200 projectors, which leads me to own three units: a halogen model from the latest series, a rare PCom, and the extraordinary Xenon version. 

Elmo GS1200 PCom 

One might assume that the world's leading expert on Elmo GS1200 Xenon projectors would be Japanese or German, but no, it's Italian, a former Italian senator, Professor Ugo Grassi, who has just published an article about some modifications to improve the switch on of the Xenon lamps on the GS1200,  which he gave me permission to reproduce here:

For many years the Elmo GS‑1200 has been my fetish object, my Zen garden where every element must reach aesthetic and functional perfection.

It is precisely the machine’s intrinsic imperfection, combined with its enormous potential, that creates a challenge whose very pursuit brings me serenity and calm.

I have disassembled, serviced, and rebuilt dozens and dozens of Elmo GS‑1200 units, including many Xenon versions.

Over time I have accumulated various spare parts and lamps, and I even had the opportunity to buy some brand‑new original Toshiba lamps (the so‑called NOS). These are short‑arc xenon lamps, similar for example to the Osram XBO series, although in a reduced, “proprietary” 250‑watt format. These lamps are ignited by a high‑voltage discharge that ionizes the gas inside the bulb.

In the world of professional film projection it is well known that some lamps strike immediately, while others take a few seconds. Even though these lamps are extremely precise components, their ignition behaviour can vary noticeably even among “fresh out of the box” units.

This is why some fire up at the very first pulse, while others seem to “struggle” for a few seconds under the igniter’s blows.

1. Electrode Geometry

In short‑arc lamps, the distance between anode and cathode is critical.

Micro‑variations: Even with very tight manufacturing tolerances, a fraction of a millimetre in spacing or in the shape of the cathode tip can change the breakdown voltage required to ionize the xenon.

Emission points: The discharge always seeks the path of least resistance. If the cathode tip does not present an immediate “preferred point” (a trigger point), the train of high‑voltage pulses must persist until the gas reaches a plasma state.

2. Xenon Pressure and Purity

The xenon inside an XBO lamp is under extremely high pressure (about 8–10 bar cold, rising to 30–60 bar during operation).

Gas distribution: At ignition, the gas density between the electrodes may vary slightly due to ambient temperature or the lamp’s orientation.

Jitter effect: If the gas mixture does not ionize instantly in the central channel, the igniter continues sending high‑frequency pulses until the main arc stabilizes under the DC current from the rectifier.

3. Coupling with the Igniter

It is not always the lamp’s fault. The projector uses an igniter that generates pulses from 25 kV to 45 kV.

Pulse frequency: If the igniter is not perfectly matched to that specific batch of lamps, you may hear the classic prolonged “ticking” before the lamp finally catches and transitions to steady operation.

I never studied electronics formally, so everything I’ve learned about the projector’s circuits comes from raw, hands‑on experience.

The first modification concerns a small resistor in the ignition circuit, R704—an apparently insignificant component that is actually decisive in determining the cadence with which the igniter attempts to start the lamp.

Working on different units, I noticed that changing the actual value of this resistor very clearly alters the behaviour of the igniter. I first realised this when I found a 100‑ohm resistor installed instead of the standard 220‑ohm one, and everything suggested it had been set that way at the factory.

With lower values, the train of high‑voltage pulses becomes denser; with higher values, the pulses spread out and the ticking becomes slower and more deliberate. By ear, it also seems that in the first case each individual pulse is less “intense,” while in the second each discharge is stronger but less frequent.

I won’t attempt an academic theoretical analysis—that’s not my field—but the empirical fact is crystal clear: R704 controls the rhythm with which the circuit attempts ignition.

On some hard‑to‑start units, adjusting R704 toward lower or higher values (100 - 320 ohm) by a trimmer finally allowed easy ignition. But not all stubborn lamps responded to this alone: sometimes the lamp would start immediately, other times it needed two or three discharge sequences, each lasting a few seconds.

The second modification concerns a much cruder yet fascinating component: the air gap—the igniter’s spark gap.

Anyone expecting something sophisticated will be disappointed. It is essentially a small cylinder containing two metal points separated by an air gap. Nothing more.

The points operate in ambient air, and for this reason not only their spacing matters, but also small construction differences, surface condition, oxidation, even the mechanical “quality” of the piece.

And here a surprising but consistent fact emerges: the distance between the two points is not the same in all units.

Some spark gaps have closer points, others farther apart. Again, the consequence is immediately noticeable.

Closer points produce faster, more regular discharges; wider spacing slows the rhythm and, beyond a certain threshold, introduces clear irregularities.

The intuitive reason is simple: with a smaller gap, the air breaks down more easily; with a larger gap, the circuit must “charge up” more before overcoming the dielectric.

Usually these small differences are irrelevant for lamp ignition. Usually…

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This modification is far more delicate.

You must open the igniter—an easy operation, since it is closed by a nylon cover held by three plastic screws.

Once opened, you discover that the components are not accessible because they are embedded in insulating resin (likely silicone).

The only visible component not submerged in resin is the air gap.

If you want to “play” with the spacing of the points, the original must be removed.

To do this, you sometimes need to carefully remove part of the resin to free the two contacts (two small metal tabs): one connected to a rigid braided wire, the other to a flexible lead emerging from the resin.

Once the two contacts are desoldered, the air gap must be extracted from its mounting base, keeping in mind that the two tabs pass through slots in the base.

At that point, you must insert the handmade air gap, ensuring that one of the points is adjustable so you can test different distances.

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At this stage it is important to emphasize that I do not know why these modifications work.

And yet they work—and they work well—without endangering the circuits.

ELMO GS1200 ACHILLES HELL

My Elmo GS1200 Xenon

I have a love/hate relationship with the Elmo GS1200 mainly because there is always a new place where it damages my movies or suddenly fails technically in one place or another. However, once repaired, I always end up using my Xenon GS1200 again, in its xenon versionwith special arms for 700 meters, or my GS1200 PCom for some sound recordings. I thank Senator Ugo Grassi for the notice, with photographs, of the true Achilles heel of the GHS1200.

Photograph by Ugo Grassi

You are "playing" with your gs1200. You think how clear the stereo audio is, how bright it is with its Xenon lamps, when suddenly the rear coil stops spinning. Or the front one no longer turns. Or the main motor no longer starts, or the film rewind doesn't even start...

Photograph by Ugo Grassi

The real Achilles heel of the GS are the two command relays. The contacts are covered with a silver/nickel, silver/cadmium oxide or silver/tin oxide metal alloy. This alloy is consumed with every spark. If you clean the contacts the projector will start working again, but the defect will return very quickly because the spark will strike the "bare" metal.

New ones command relays can be ordered HERE

Photograph by Ugo Grassi

ABOUT CLAW POSITION IN SUPER-8 (FOR CAMERAS AND PROJECTORS): LOOKING FOR PERFECT STEADINESS WITH SUPER-8 FILM

When Super-8 was presented, one of sales arguments to convince that part of the filmmakers who defended the better image stability of other motion pictures small gauges, was the standardisation of the claw position both in camera and projector.

In the original specification matching claw position in camera and projectors, the film is moved downwards by the claw. In the picture, the perforations are numbered -1, -2, -3... above the window gate, and +1, +2, +3 below the gate.

The design of the Super-8 cartridge is such that the camera claw is such that the camera claw must enter the perforation at -3, pull the film down and then leave the perforation at -2. The whole point of the Super-8 specification is that, in the projector, the claw should be in the same position relative to the gate as in the camera, entering perforation -3. 

The argument in favours of this standardisation is that, if the perforations are unevenly spaced along the film, it will still be possible to project a steady picture, because the same perforation is being used to position the frame in the gate both in camera and projector. But, is this matching really worth while? 

Fumeo projector double claw before pull down: frames + 1 and + 2 (photo from IB Cinema archive)

NOT APPLICABLE TO SUPER-8.

In order to get good steadiness in film projection, a first essential is that the perforating of the film should be done with with accuracy and precise uniformity of spacing, otherwise, it would not be possible to obtain a steady projected picture.  When the 16 mm gauge came along, in 1923!!!, this  in general was perforated accurately, and the majority of 16 mm users were always well satisfied with the steadiness of their pictures,  regardless of the claw position in the camera or the projector. 

It was not until the 8 mm double-run film-stocks became popular for amateurs (over 9.5 mm or even 16 mm), in inmediate post II W.W. years, that complaints of serious unsteadiness began to be heard -and one reason for this trouble was that some of the double-run film-stocks then available were in fact 16 mm film which had been re-perforated to add additional perforations in between the existing 16 mm ones. 

Fumeo 9145 xenon projector (2.200 meters reels)  with claw after the window gate

In the 50´s some of the 16 mm being re-perforated was ex-war stock  which had been stored for some time and which had shrunk. Then, the spacing between "new" and old successive perforations would be alternately long and short. If this stock was shot with the typical double 8 camera, which the claw ends its pull-down at +2, after reversal processing, when the film was run in a projector in which the claw ends its pull-down at +3, the result was the picture on the screen will not be steady. 

Thus, we see that certain 16 mm film reperforated to Double-8 mm can be unsatisfactory if the claw positions in camera and projector do not match. 

But is this a valid reason for standardising on matching positions for Super-8 equipment?

Fumeo projector double claw after pull down: frames + 2 and + 3 (photo from IB Cinema archive)

The answer is no. Unlike Double-8, super-8 film cannot be made by adding additional perforations to 16 mm, because the pitch is different (16 mm has 40 frames per foot and Double-8 80, but Super-8 has 72 frames per foot), and there seems little possibility of badly-perforated Super-8 stock coming onto the film market. 

The accuracy of perforation of film-stocks from manufactures as Kodak has always been very high, and there really doesn´t to be much point in making Super-8 projectors conform to the camera standard. So, matching claw positions in Super-8 cameras and projectors is not necessary. 

ZC1000 double claw after pull down: frames + 3 and + 4 (photo from IB Cinema archive)

THE BEST SUPER-8 PROJECTORS HAS THE CLAW BELOW THE GATE. 

It may be noted that not all Super-8 projectors have conformed with the standard claw position, notably the prestigious Fumeo, Microtechnica and Heurtier projectors, all of which have the claw below the aperture (Fumeo Super-8 projectors are +1 + 2 to down +2+3, and  Fujica ZC1000 is  +2 +3 to down +3+4). From a technical point of view, it is always better to "pull" the film from below the window gate than to "push" it from above. Professional projectors in 16 mm or 35 mm always use the perforations under the gate window, with claw or Maltese Cross.

Shooting in 2023 with my ZC1000N near Mount Erebus, in th South Pole, at -35º Celsius

WHAT ABOUT S8 CAMERAS WITH PERFECT STEADINESS?

• Why do Super-8 cameras have the claw pull down before the gate?, unlike most other film formats, including Single-8, which uses the same 8mm S-type film. This is because to the coaxial design of the Super-8 cartridge and its poor drag for film advance. With these cartridges, if the claw is below the gate,  it would cause unesteady images and jams, as they discovered during the development of the Super-8 cartridge.

But most of Single-8 camera models, not only from Fuji, but from Canon and Elmo too, also have the claw below the window gate. I have projected these 8 mm type S films shot with Single-8 cartridges for years on projectors with claw over the gate,  as the Fujicascope SH30, Braun Visacustic or the Beaulieu Studio, among others, always with perfect steadiness. In one of these stantardized projectors, films shot with the Canon 518SV in Single-8 version provides a more steady picture than the one obteined using same model for super-8, despite the fact that the latter has the standardized claw position matching with non professional projector.

Canon DS8

I have filmed a lot, during the last 4 decades, with two cameras, according to my results, able to give me the best steadiness ever obtained with projected revesal film original: both models has the claw below the gate. One is the Fuji ZC1000 (S8 film in Single-8 cartridge), the other one is the Canon DS8.

Canon DS8 claw after the window gate

• I wrote this article in the hospital, at the request of Italian Senator Ugo Grassi

In next video, Fumeo 9135 Xenon Stereo Super-8 projector being used with an anamorphic print of "El Cid" (Lone Wolf edition, LPP poliester, Castilian track) in a 6 meters wide screen: 

More information: ZC1000N