Kinematograph year book (1944)

210 The Kinematograph Year Book. A. Cotton, Ltd, — War conditions have made it impossible to meet all demands for the famous t: Solar Blue r: mirrors; but special permission was eventually obtained for the resumption of manufacture, and supplies were again available to exhibitors through their suppliers. Limited quantities of white mirrors are also available. Excellent facilities exist for the repohshmg, on specially designed machinery, of mirrors of all types and also for resilvermg, CONVERSION PLANT. THE inotor generator is now almost superseded on A.C. mains by various forms of rectifiers. The general principle employed is the thermionic valve. The mercury rectifier has for years been used for supplying projector arcs, and another type in wide use, particularly for lighter loads, is the oxide-cathode. The advantage of both these types is that they require practically no maintenance other than, in the case of the mercury rectifier, the usual attention to ths fan motor. Another type in increasing demand is the metal rectifier, which employs copper-oxide, a development of which, before the wrar, was the introduction, as an alternative, of selenium , which has the advantage that it can be run at a much higher temperature than copperoxide. There have been fewT developments during the year, although Hewittic's Econotrol is more compact in form than when first introduced. Users of oxide-cathode equipment appear to have little complaint of tbe efficiency of the substitutes for the type 1738 and 1749 valves, which were introduced at the end of last year. The threatened shortage of rectifying valves, however, led to the demand, since well maintained, for the installation of an inductor with A.C. arc, as an alternative, either for immediate use or as a standby. Most of the specialists in rectifiers are developing their equipment. British Thomson-Houston Co., Ltd.— The B.T.-H. hot-cathode type utilises three mercury vapour valves (two valves are used for single-phase supplies), and can be supplied for continuous ratings up to 120 amp., suitable for 75-amp. arcs. In the case of three-phase equipments, two valves will carry the load for a short period, should one valve fail, warning of which is indicated by a special device. The B.T.-H. glass-bulb rectifier can be supplied for any rating required in kinemas. Generally, a single-bulb equipment is used, but for increased safety-factor a twin-bulb equipment can be supplied, having two bulbs operating in parallel or with the second bulb as stand-by. Crypton Equipment, Ltd. — -War conditions have naturally affected the activities of all manufacturers, but this is particularly so with the Crypton Equipment, Ltd., who, apart from problems of w<ar production, have been forced by enemy action to establish a completely new factory at Bridgwater, Somerset. The many difficulties arising from the re-establishment of production have since been satisfactorily overcome. Plans are in hand which will ensure the firm having a very attractive range of modern equipment available for the trade immediately peace trading conditions return. Electric Construction Co., Ltd. — The low running costs of the Electric Construction Co.'s high efficiency double-bulb mercury arc rectifier commends this equipment to the exhibitor. Each unit feeds one 45volt 65-amp. direct without stabilising resistance. Each bulb is of the 6-arm type, only three of them being normally in use. This arrangement, it is claimed, provides complete " standby," as, if necessary, both arcs can be run from one bulb by using all six arms. Hewittic Electric Co., Ltd.— The past year has been notable for a heavy demand for Hewittic " Econotrol " rectifiers, the needs of the Forces having endorsed the well-established excellence of this equipment. In its latest form the " Econotrol " rectifier is even more economical and at the same time more compact than when first introduced, and it is the constant endeavour of Hewittic, by steady development, to maintain this equipment's leading position in the field of cinema rectifiers. Hewittic battery charging rectifiers have also been developed during the past year in new, compact and easily installed types, and there is no direct current demand in the kinema which cannot be most effectively met by one or other of the Hewittic types available.