Kinematograph year book (1939)

282 The Kinematograph Year Book. lamp reaches full operating brilliance as rapidly as the ordinary domestic incandescent lamp. In operation, the discharge is perfectly stable and the luminosity evenly distributed. Taking only 1 k.v.a. from a D.C. power supply, its economy in running costs is immediately apparent, while the use of D.C. completely eliminates the flicker which would be caused by the " beat " between shutter and lamp if it were operated from an A.C. supply. The low temperature of the lamp means a complete absence of the heat, fumes and dust inseparable from a carbon arc, and therefore less wear and tear on the film and greater comfort for the projectionist. Moreover, since the lamp requires no supervision, the latter is left entirely free to concentrate on the running of the show. This feature, together with the extreme compactness of the lamp and its holder, makes it possible to locate the assembly close to the film gate, and in practice the projector and its light source are mounted on a circular plate, which can be rotated about its horizontal axis to adjust the vertical angle of the throw. The space usually taken up by the lamphouse is thus left clear to accommodate the spool boxes, which are arranged in line behind the projection unit, and the complete assembly is mounted on the side of a cabinet which contains the photocell amplifier, driving motor and so on. The horizontal dimension is about the same as that of a typical projector employing an arc lamp, but the vertical dimension is so small that it is possible to mount two projection units, one above the other, on top of the amplifier cabinet. The latter, which is a strong rectangular metal construction, houses the amplifiers, their power supplies, controls and monitor loudspeaker. The fact that all speech wiring is contained inside the cabinet makes for excellent screening and short speech connections, eliminating any tendency to line loss, cross talk, instability and hum. All the wiring and components are immediately accessible simply by removing the cover plates on the back of the cabinet, which exposes the complete layout in a matter of a few seconds. This efficiency arrangement occupies only about half the floor space required by the usual pair of projectors, and since it is completely self-contained, there are no controls or equipment to be mounted on the wall of the operating box. Thus the complication and expense of installation are reduced to a minimum. The equipment is delivered with all the internal wiring already in place, so that the only connections to be made are the outgoing pair to the loudspeakers and the incoming power supplies — a total of three pairs only. PROJECTORS AND PROJECTION EQUIPMENT. British Thomson-Houston Co., Ltd. — B.T.H. projectors of the latest design are available in two types, the first being the standard model, utilising the highlysuccessful fireproof spoolboxes, while the second type incorporates normal spoolboxes. In both equipments the projector mechanism is the same and embodies the well-tried system of reflector cooling. Despite the increase in arc-lantern efficiencies with consequent increase of heat in the beam, developments have proved it possible to make the picture gate even cooler. These projectors also include a special built-in changeover device fitted at the back of the equipment — the ideal position. The device is sufficiently robust to withstand the heat of the arc lamps indefinitely, and thus forms an additional safety feature. The success of the B.T.H. 50-ampere arc lantern and also of the low intensity arc lantern has necessitated little change in design, and only a few minor modifications have been made. A newcomer to the range of arc lanterns is the Type 4i F " equipment, which utilises automatic feed with copper-coated high-intensity carbons. This is designed for currents between 40 and 50 amperes and for use in smaller theatres requiring high-intensity results.