This is from a hand written WWII notebook by the R.A.O.C. York. Written 20-25/10/40.

This chapter is about the Bell & Howell Sound Projector. All the hand drawn diagrams have been digitally remade as close to the originals as possible.

The Bell & Howell Sound Projector.

By R.A.O.C. York. Circa 20-25/10/40

The B. & H. Sound Projector is divided into two parts. The mute head in which the picture is reproduced. The sound head in which the sound is reproduced.

The mute head. No belts, everything is driven from the motor. The motor is universally wound & the speed is fixed. A switch can change the speed from 24 pictures p.s. (Sound) to 16 pictures p.s. (Silent.) Motor takes D.C. or A.C. Voltage. 110v. 1/24 HP. The Amplifier will only take A.C. Current. In front of the motor is the lamp house, containing the lamp. At the rear of this is a reflector which can be adjusted laterally to get correct & even illumination.

The lamp is 100v. 750w. Bunch filament pre-focus type. When removing a lamp, care must be taken to avoid damage, & when replacing the contact no force must be used. Situated in their seating in front of the lamphouse are two condenser lenses. The front lens increases light by 25%. The gate is sprung, & the claws of the Pull down mechanism are situated on the outside of the gate. The rear plate of the gate has a fixed aperture. The front plate is sprung, & the aperture can be moved up & down to centralise the picture.

The object lens is a 2” focal lens & can be adjusted quickly or finely as desired by pulling or turning respectively. A locking screw is provided. The gate lever for opening & closing is situated to the rear of the object lens housing.

The inching knob is situated to the rear of the gate lever. It is for testing of the threading of the film.

The still picture device is operated by a lever to the rear of the inching knob. This lever throws the sprockets & the claw mechanism out of gear from the motor. When this device is in action, a gauge wire shutter drops between the light and the picture in the gate,When the device is not in operation & motor is running, the draught from the fan keeps the shutter up. When the device is applied, the draught is diverted from the shutter & it drops.

A sprocket is mounted above and below the object lens housing. The top sprocket which feeds the film to the gate has a roller & guide to keep the perforations in contact with with the sprocket teeth. The bottom sprocket also has a guide for the same reason. The guides are automatically closed when the gate is closed. A pilot light is fitted above the gate,

The sound head. On the front of the machine is the exciter lamp. 10v.7.5a. 15w. Single coil filament. When in correct alignment, the filament of the lamp is in line with a line on the machine. To adjust the lamp fir height, loosen the 2 seating screws & it can be adjusted. To the rear of the exciter lamp is the exciter tube, which condenses the rays of the lamp to a small bed of light .05” long & .0005” wide. To the rear of the exciter tube is the sound drum. This is rotated by the film passing over it, & has a flywheel on its spindle to ensure smooth turning. Above the sound drum is the tension pulley, which ensures the film is kept tight round the sound drum. When the film passes round the sound drum, the sound track overhangs the edge of it. It is at this point the exciter lamp rays pass through the sound track.

Mounted on the inside of the sound drum is a 45° mirror which reflects the light through the sound track onto the photo-electric cell. The rays from the exciter lamp pass through the exciter tube onto the sound track of the film, the waves of light that come through the sound track are reflected onto the Photo-electric cell by the 45° mirror inside the sound drum. The P.E. Cell changes the light waves into electric impulses which are passes to the amplifier & onto the speakers, & leave the speakers as sound waves. Above the sound drum is the sprocket which takes away the film after it has passed over the sound drum.

To remove the amplifier. Drop the front leg to fullest extent. Remove 4 knurled screws from bottom of machine. Remove connection from exciter lamp to amplifier. When amplifier is removed, cover up the photo-electric cell. After replacing amplifier ensure all valves are tight in their seatings, P.E. Cell is in place & the exciter lamp connection is plugged in.

To set up the machine. Remove machine, speakers, transformer from boxes. Set up machine on stand, erect the screen & place the speakers as near the screen as possible. Ascertain correct mains voltage from motor & set it in transformer. Screw take-up & feed arms into the case. Connect belts to take-up arm. Make all connections to speakers, machine, amplifier & transformer before plugging into mains supply. Switch on mains, & test the motor on sound & silent speeds. Switch off motor when changing from sound to silent speeds. Switch on lamp & make sure it dosen’t light until motor is switched on. Test the draught to see if fan is working properly. Make sure safety shutter is lifted. Focus the light to the screen. (max distance 40ft.) Test still picture device. Switch on exciter lamp & prove correct. Plug in microphone & test amplifier & speakers by speech. Turn V. control on full & see if exciter lamp increases in brilliancy. Place a slip of paper through the rays of light from the exciter tube & listen to the plop plop in the speakers. Thread the test film into the machine. Start machine & adjust volume & tone control. Test still picture device several times & note approximate positions of volume & tone controls.

1. REFLECTOR.
2. LAMP.
3. CONDENSER LENSES.
4. FIXED GATE.
5. FILM.
6. MOVEABLE GATE.
7. LENS.
8. SCREEN.

Fig. VI LIGHT circuit. B&H. MACHINE.

1. EXCITER LAMP.
2. EXCITER TUBE.
3. FILM.
4. 45 MIRROR.
5. SOUND DRUM
6. PHOTO-ELECTRIC CELL

Fig. VII SOUND HEAD. B&H. MACHINE.

		S.	SPROCKETS.
		S.D.	SOUND DRUM.
		P.	PULLEYS.
		R.	ROLLERS.
	SW.	1.	SOUND OR SILENT.
	…	2.	LAMP.
	…	3.	FORWARD OR REVERSE.
	…	4.	MOTOR.
CONTROL.	1.	VOLUME.
	…	2.	TONE.
	…	3.	“MIKE” VOLUME.
		T.P.	TENSION PULLEY.
		O.L.	OBJECT LENS.

Fig. VIII THREADING UP. B&H. MACHINE.

Fig. IX THE B&H. SOUND PROJECTOR.
EX. CASE & SPOOL ARMS.