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Rebuilding of a HOLMES 35mm sound projector

By Ed Jurich

Holmes 35mm projector

The HOLMES was built during WW2 and used for showing movies to our armed forces
It still runs good and gives a fine show with a few improvements

In 1960, while in high school, I worked for a small theater chain on the south side of Chicago. At the time I had no knowledge of the Holmes projector but one day we had a substitute operator filling in and I was up in the projection booth talking to him. I think his first name was Elmer, his last name was Holmes and it was his father that had the Holmes projector company. He was telling me a few stories and it turns out that the reason there is a sound gate and not a sound drum ( stabilizer ) is because Holmes refused to pay RCA royalties. Although there is no drum there is a flywheel on the back side of the sprocket that pulls the film through the gate. This system works pretty well on the 35mm projector but apparently not so well on 16mm with the slower film travel.

THE PROJECTOR was completely taken apart and gone through as described in the following paragraphs. Several modifications were incorporated. The case paint was stripped and repainted with a now discontinued industrial quality RUST-OLEUM epoxy paint that came in spray cans. The case was painted in 1993 and so far has resisted chipping. The projector inside the case is still the original gray.

THE GEARBOX is still original, the only work I did here was to clean out all the old grease and re-pack with new grease. Re-packing the grease was the first thing I did using axle grease around 1991. I replaced the grease in the gear box recently with grease made by the same folks who make Slick50. This grease has Teflon in it and seems to be less oily than other grease. So far I haven't had any oil drip from the gearbox.

THE SOUND ROLLER'S, the two roller's before the sound gate in the original Holmes design are fixed in position. Being fixed, there is no way to keep the film tight through the film path from the sprocket after the intermittent to the sound gate. This causes a couple problems. Depending on the slack, the film rides up some off the sprocket after the intermittent. Also, if there is too much slack, the film jumps off the back end of the roller before the sound gate. The back end of the roller before the sound gate has a spring in it to keep the film positioned properly in the sound gate.
To correct this problem, an adaptor for one of the roller's was fabricated allowing the roller to be spring loaded and compensate for slack in the film.

THE OLD FIRE ROLLER'S for the feed and takeup reels were modified so that thick splices will pass. The original roller's were very close and thick splices would not pass.

TAKEUP ROLLER MODIFICATION added to the projector to absorb the shock from the takeup reel jerking the film from the last sprocket. Different factors such as how loose the takeup belt is or if the takeup reel is full and you are restarting the projector can cause the takeup reel to hesitate for a moment on start-up. This causes the film to slightly slack off the last sprocket and then get jerked as the takeup reel gets up speed. This can snap old brittle film so a spring loaded roller assembly was fabricated and added to absorb any shock from the film being jerked by the takeup reel.

THE SOUND PICKUP has been modified with the old photocell being replaced with a stereo photo-transistor pickup. The photo-transistors are mounted to a small metal bracket that mounts from the back side of the projector, through the old photocell socket hole.

THE PRE-AMPS for the pickup are mounted to the same bracket as the photo-transistor pickup. The photo-transistors double as the sound pickup and first stage of amplification. A second transistor follows the photo-transistors for a total of 55db of gain. The sound output is in the front of the projector like original but with a stereo (3-circuit) jack.
There are two small hand made circuit boards, one has all parts for the photo-transistor electronics and the other has the electronics for the second transistor stages. The circuit board for the photo-transistors is mounted on the underside of the bracket. The circuit board with the second stages is mounted on the top side of the bracket. It is fairly tight but there is plenty of room for the original cell cover to fit over the new assembly.

THE SOUND PICKUP COVER is the original photocell cover. The stereo photo-transistors are positioned at the cover hole. The photo-transistors are about 3/4 inch from the film. The scan beam from the soundtrack spreads as it leaves the film. The separation between the photo-transistors is right for the amount of beam spread at this distance.
Because of the beam spread, a vertical divider is used between the photo-transistor to help keep the left and right channel beams from completely crossing each other. The cover is modified with a hood that holds a vertical divider attached to the cover opening. Because the sound gate needs room to open, the vertical divider is about 2/5 inch from the film so there is some beam spread cross-over before it reaches the divider. The added hood also helps shield the photo-transistors from stray light.

THE LAMP HOUSE has several changes. First I wanted to replace the original 1000 watt bulb with a lamp that was less expensive to replace. Besides the high cost of replacing those old original lamps, the original reflector had no silver left on it. I decided to go with an ELH 300 watt lamp which has a self contained reflector and operates on 120VAC. Although the new lamp won't fill a 20 foot screen, it is plenty bright for the 6 foot picture at home.
Another change to the Lamp House was to get rid of the belt driven blower and asbestos heat shield. I constructed a new Lamp House cover with a built on box fan blower. The new cover is made of 14 gauge steel and much more sturdy than the original. An addition to the Lamp House is the exciter lamp power supply. I wanted the projector to have a self contained exciter supply and sound pre-amp. Since space is so tight, I decided to use a single supply for both the 4V exciter lamp and the 28V sound pre-amp. The large filter capacitors and voltage dropping resistors I mounted on a plate in the bottom of the Lamp House.

THE EXCITER LAMP was changed to a lower current type to reduce the size of the needed power supply. Also, the newer lamp has a thinner filament which provides a thinner scan line for a better high end response. It is a BAK 4-volt .75 amp lamp. Although the new exciter lamp generates less light then the original exciter, the original photocell has been replaced with photo-transistor pickups that require less light. I found that the original exciter lamp socket holds the new lamp good and alignment works well.

THE SWITCH BOX containing the threading light, motor and lamp switches has also been modified. The circuit has been changed and includes single pole switches for motor and lamp, a fuse for the motor and lamp circuits, a transformer & rectifier for the exciter lamp & sound pre-amp and a power cord with a three prong AC plug for ground.
The new transformer is mounted on the back side of the switch box enclosure. Terminal strips have been mounted inside the box for the rectifier circuit and all projector circuits to terminate. The new fuse is mounted inside the box but removing the cover provides easy access to the fuse.
Ground wires run throughout the projector grounding the motor, Lamp House, switch box and projector case.
The original power cord and lamp sockets on the switch box have been removed. A new plate has been fabricated and installed on the switch box in place of the old connectors. Large holes and rubber grommet's provide holes for the AC cord and Lamp House wiring harness.

THE FILM GATE has been modified so aperture plates can be inserted. This is mainly for the newer aspect ratio of flat movies. For older prints the aperture plate is removed and the original aperture is used.
The film gate is made out of hardened steel and a file won't work so the original aperture remains. For cinemascope, the picture will be cut off a little at the top and bottom so it'll be a really wide picture.

THE MAIN DRIVE ball bearings went out on me. When I tried looking for new bearings I could not find exact replacements with the tapered offset. Instead, I purchased standard flat ball bearings and then added flat bearing washers to the main drive gear. I found no real need for the tapered bearings, the flat bearings clear the main drive gear housing fine. The washers I added position the main drive gear for proper mesh.

THE CUSTOM AMPLIFIER is a new 3-channel, 10 watt per channel solid state amplifier. The original tube type amplifier was in very bad shape and with the new stereo pickup a stereo amplifier was needed. The three channels are left, right and sub-woofer used to drive a bass speaker.