Projection engineering (Jan-Dec 1931)

Page 28 PROJECTION ENGINEERING LIGHT RELAY AND LIGHT SOURCE UNITS Complete, ready-to-use light relay and light source units of extreme simplicity, ruggedness and reliability, are announced by the Radiovisor Division of the Burgess Battery Co., 202 E. 44th St., New York. The units are designed around the novel Burgess Radiovisor Bridge or light-sensitive cell. The Burgess light relay units are available in both a-c. and d-c. models for use on usual power supplies. The units are in the form of an aluminum housing with window, containing a circular platform on which the bridge, tubes and other components are mounted. The a-c. unit comprises bridge, two 427 type tubes serving as amplifier and rectifier respectively, power transformer, filter condenser, resistors, by-pass condensers and power relay. The d-c. unit comprises bridge, one 427 type tube serving as amplifier, voltage reducing and other resistors, by-pass condenser and power relay. The unit housing is held by a wall bracket ring, permitting necessary adjustments to line up the window with the actuating light source. When provided with the Burgess vacuum contact, the light relay can control a circuit handling up to 1,320 watts. A PAM PUBLIC ADDRESS SYSTEM The Midget, the new Samson portable PAM address system consists of a PAM 71 speaker amplifier, MIK 71 microphone amplifier, and a dynamic loudspeaker compactly and permanently fitted into a small carrying case. All of the accessories — microphone, cords, plugs, etc., — are stored in separate compartments of the case made especially for the purpose. For gatherings up to 500 people the Midget PAM address system offers exceptionally high-quality equipment at an extremely low price. It has a wide variety of uses. The Midget is manufactured by the Samson Electric Co., Canton, Mass. ▲ VISITRON SALES SHOW MARKED INCREASE Sales of Visitron photoelectric cells made through National Theatre Supply branches, have recently increased more than fifty per cent, according to G-M Laboratories, Inc., of Chicago. The increase is attributed to the known fact that many exhibitors are now getting their projection equipment in proper order for Fall business, and to a general realization of the importance of the photoelectric cell as a necessity to better sound performance. Although properly constructed cells have a very long life expectancy under average conditions of operation, they should nevertheless be inspected and tested periodically for output and operating efficiency, inasmuch as they are vital to correct talking picture presentation. The importance of making a thorough examination of sound equipment in preparation for the coming season cannot be over-emphasized, and of all parts of the sound equipment there is no more vital part than the photoelectric cell. A NEW PHOTOELECTRIC CELL The development of the Weston photronic cell, with its amazing performance characteristics and its utter simplicity of design marks a sensational advance and fulfills the need for an ideal type of photoelectric cell. Notwithstanding the superiority of this Photronic Cell, it is exceptionally low in cost as is also its auxiliary apparatus. Its discovery now places photo cell equipment well within reach of every amateur experimenter. Electronic in its character, the Weston photronic cell employs a highly light sensitive disc which transforms light energy directly into electrical energy without the use of any auxiliary voltage whatsoever. Its response to light variations is instantaneous and sufficient current is developed to directly operate relays without the use of auxiliary apparatus or any battery. It delivers about one microampere per footcandle of light intensity. When exposed to direct sunlight the output is approximately 5 milliamperes. The. cell resistance varies from about 1500 ohms for 10 foot-candles light intensity to about 300 ohms for 240 foot-candles intensity. As far as is known, the life of the cell is practically unlimited and a continuous current flow does not harm it in any way. Since it does not contain any liquid nor require vacuum or gas, there is nothing to get out of order as it is not subject to physical or chemical change and it has a constant output. It can be exposed to direct sunlight without deterioration, has no dark current since its energy is derived directly and only from light ; no drifting, hence no circuit adjustments are necessary; no fatigue and it is non-microphonic. The photronic cell is enclosed in a handsome moulded black Bakelite case fitted at the bottom with two connection prongs which fit into the standard UX radio tube socket. It is rugged in construction and is so simple in design that there is nothing to get out of order. The case is 2*4 inches in diameter and 1 inch in thickness. ▲ CLAROSTAT SPONSORS DUAL VOLUME CONTROLS OF IMPROVED DESIGN In line with the trend towards increased compactness in the design of radio parts, Clarostat engineers announce an improved type of dual volume and constant impedance controls. These latest additions to the Clarostat line, include in their construction all the advantages which have popularized the older model Clarostat dual controls. The new models, however, contain special features which greatly increase their efficiency and utility. A new coupling arrangement results in a very sturdy unit and eliminates all chance for lost motion between the ele ments. An electrostatic shield is provided between the two potentiometers. This is often of considerable value in preventing undesired coupling between the two circuits. The new Clarostat dual controls are much smaller than previous models and project only 1% inches behind the mounting panel. These controls are available with any combination of resistance elements, with standard or reversed taper, either with or without the new built-in 110-volt switch recently announced by the Clarostat Company. A DUNCO INTRODUCES LOW COST LIGHT SENSITIVE CELL UNIT Much has been expected, and much has been accomplished by the light sensitive cell, but, until now, its full application has been rather restricted due to the high cost of these units — usually a hundred dollars and over. Now, however, Struthers Dunn, Inc., 127 N. Juniper Street, Philadelphia, have announced the Dunco light sensitive cell unit which lists at $30, less tube. This unit is housed in a case 6x5x3" overall, having an aluminum finish. It operates on standard voltage, 110 volts, 60 cycles, although special sets, both a-c. and d-c. can be built to order for voltages other than this. The Dunco uses a standard 112-A tube. As is the case with any light sensitive cell unit, the new Dunco unit will operate at practically any distance, being limited only by the distance that light can be thrown. Either reflected or diffused light will operate the unit, which is adjusted at the factory for operation requiring a ten-watt lighted lamp being placed one foot away. This is without the use of any reflecting device. The unit, however, can be adjusted for more sensitive operation. A INTERNATIONAL PROJECTOR MARKETING NEW PORTABLE Acme 35 mm. portable projector and sound-film reproducer, designed primarily as a portable unit, but equipped with a complete professional optical system for use in moderately-sized auditoriums, and in small theatres where a picture of the maximum size of 12x16 feet is desired, is being marketed by International Pro jector Corp., 90 Gold St., New York City. Entire assembly weighs about 100 pounds. This new equipment, simple in operation yet sturdy in construction, consists of a portable motion picture projector and sound reproducing equipment of fundamentally new design. The condensing system consists of the Bausch and Lomb Cinephor PM-15 and PM-25, and projection lens mounts are so constructed that any type of lens may be used. This means that the full-size, No. 2 or Series II lenses may be readily accommodated in any focal length. The sound reproducing equipment is said to have received equal consideration in its construction. The exciter lamp socket is rugged and the optical system is sturdy and rigidly mounted. No tension shoes or springs, in the sound reproducing gate, are used at the sound take-off aperture. The film after leaving the sound gate feed sprocket is passed over a roller and tension is applied at this point. The amplifier used with the Acme portable equipment is the product of RCA Photophone, Inc., and is completely operated. It is mounted in a carrying case and weighs approximately 40 pounds. A system of changeover switches has also been developed for use in connection with two of these new Acme projectors so that a sound-on-film program may be projected with equal ease and with the same results as obtained in a modern theatre, the company declares.