Projection engineering (Sept 1929-Nov 1930)

Page Projection Engineering, April, 1930 ELECTRODYNAMIC SPEAKERS For public-address systems and theatre purposes a line of loudspeakers are manufactured by Victory Speakers. Inc., 7131 East Fourteenth Street, Oakland, California. Among the new principles used in the construction of Victory speakers Is the concentration of the field energy and an intensification of the magnetic flux at four points on the top plate with a more pow erful drive to the movable coil; breaking up an otherwise undesirable eddy current set up around the pole pieces. In these speakers there is no shell around the field coil. The outside cover is designed to give perfect ventilation to the field coil which reduces the operating temperature to a minimum. All terminals are grouped in a single bakelite plate on the rear of the speaker. NEW TYPE SUPERIOR RESISTOR A new development by the Superior Resistor Corp., 344 Badger Avenue, Newark, N. J., is their Type AT-50 and BT-10 wire-bound resistor. This unit was designed to meet the demand for a resistor that could be mounted directly on a metal or other panel without the use of a separate insulated mounting. The resistor is wound on the usual Lavite bobbin but has a shoulder turned on either end to form an insulating mounting for the complete unit. It may be secured to the panel by the use of a No. 6 screw. The uses to which a unit of this type can be put will readily be appreciated by those interested in the design of sound-picture projection, television, screen-grid circuits, vacuum-tube voltmeters, radio receivers, etc. Resistance values from .25 ohm to 2 megohms, with an accuracy of 1%, or less if desired, may be obtained. From .25 ohm to 100,000 ohms the bobbin is %-in long by %-in. in diameter and will safely cany % watt. The higher values, up to 2 megohms, are wound on 1%-in. long bobbins and will safely carry 1 watt. From the above it is evident that these resistors will make ideal units for fader and volume controls, grid bias, plate resistors, and in fact will be found to fill a long-felt want for many other purposes than those mentioned above. JENKINS EXPERIMENTAL RADIOVISOR \iminfc tc provide the iverags radic Experimenter with a device affording immediate results in radio television reception, yet permitting of subsequent alterations and additions, the Jenkins Television Corporation of Jersey City, N. J., now announces its Model 100 radiovisor. This device includes scanning disc, motor, lamp and magnifying lens for the reception of standard 48-line. 15 pictures per second radiovision signals. Attachments available in the future will permit of receiving other standard signals. The motor of the Jenkins radiovisor is unique. It is of the Faraday eddy current type, comprising six electromagnets operating in conjunction with a toothed rotor and a copper disc, and operates as a synchronous motor, or automatic synchronism when used on the same a-c. power system as the radiovision transmitting station. A speed control permits of slight variations in speed, so that the scanning disc may be brought to exact speed when operated on a different power system than the transmitter. The operation of the radiovisor is practically silent. The television lamp is contained in an attractive lamp house. By raising or lowering the lamp house, or shifting it either way, the pictures may be properly framed. The images are viewed through a powerful magnifying lens. The accuracy of the scanning disc, together with reasonable magnification, makes for clear, well-illuminated images. The Jenkins radiovisor may be employed in combination with a suitable short-wave receiver and amplifier. A special radiovision receiver, developed by the Jenkins engineers, simplifies the problem of a complete radiovision set in combination with the radiovisor. THEATRE FILM INSPECTION The Film Inspection Machine Co. 630 Ninth Avenue, New York, is now putting on the market a film inspection machine having some new features to meet the new conditions brought about by the sound films. This new model is for use in the theatre or exchange. The use of this machine which is really an instrument of precision, though simple and dependable, will, it is stated, accomplish many very desirable results. A LYNCH RESISTORS Many advances have been made in the design of resistance units since their earliest use, but a most outstanding improvement is the molded end cap which is a feature of the metallized dynohmic type. No longer is there a possibility of relative movement or corrosion in the unit itself, while a maximum contacted area and minimum contact resistance is provided for. These cast metal end caps insure positive electrical and mechanical connections. They cannot loosen since "i'V are actually integral with the resistance element and its protective tubing. The tinned copper pigtail leads, whether flexible or rigid, are molded into the caps and are not soldered or strapped thereto. The cap itself is tapered for insertion in standard cartridge type mountings where interchangeability is desired. By this method a clean, sure contact between resistance element, cap and pigtail is made certain. The resistance element itself is based on the metallized principle which has been universally accepted where accuracy and uniformity are of paramount importance. This metallized resistance element is produced under laboratory conditions which provide a continuous and careful check for accuracy throughout its entire length in the making. Subsequent tests include "flashing" at double the rated wattage of the unit. Because of its design the completed unit comprises many advantageous features. The current travels a short and direct route in passing through the resistor which is non-inductive and without measurable capacity to cause feedback. The special ceramic casing is of sturdy construction and maximum heat dissipation. It will withstand more than average shocks and jars as well as minimize the possibility of damage by crushing. The above features have led to the adoption of the metallized dynohmic type of resistor by leading engineers in many fields, and is but one example of the painstaking research which, constantly carried on, leads to the development of better apparatus. PREVENTS GATE FROM WARPING The Chicago Cinema Equipment Company, 1736 N. Springfield Avenue. Chicago, 111., has completed experiments along lines which makes practicable the cooling of aperture gates, of film, and avoids warping of gates due to heat. DWORSKY FILM MACHINE CORPORATION The Dworsky Film Machine Corporation, Long Island City, N. Y., has issued a new catalog, illus trating their automatic enclosed rewinder, cleanerwiper combination, projection hand rewinder and film renovator. PHOTOELECTRIC CELL AND AMPLIFIER UNIT A photoelectric cell with an amplifier is now sold as a unit by the Westinghouse Electric and Manufacturing Company. The photoelectric cell, often called the "electric eye," is a light-sensitive device. When light falls upon it, voltage having been applied to the cathode, a current passes by means of electron emission from the cathode to the anode. This current is very small, but, when amplified, operates commercial relays. The photoelectric cell has helped to make possible many operations previously considered impractical. It has aided in the perfection of talking motion pictures, television, automatic smoke detection, recording of smoke density, and other accomplishments. For some applications, complete apparatus has been developed and can be supplied as a unit; but for most applications where no standard apparatus is available, the photoelectric cell with its amplifier is sold as a unit to be applied by the customer. The amplifier unit, shown in the illustration, consists of a die-cast aluminum box in which are mounted the necessary coupling 'devices. The top, which is a Micarta panel, is provided with two fourprong bases for mounting the photoelectric cell and the amplifier tube. All of the wiring is concealed, connections being made to binding posts on the top panel. The unit is dust-proof and moisture-proof. The short connections in the unit make possible a very high speed response — between .0001 and .001 seconds. Although four prongs are supplied in the photocell, for mounting in a standard four-prong base, only two are connected — the anode and cathode prongs. The cathode plate or cell window, which is coated with caesium, the light-sensitive material, faces the two large prongs. Industrial engineers and experimenters find this device applicable to tasks now requiring tiresome watching by the human eye. Some of the many applications are: sorting materials, according to color, size and shape; counting items, where mass production requires speed; initiating operations, such as ringing an alarm on a paper machine when a break occurs in the paper; lighting control, for turning on and off artificial lights according to the intensity of the natural light; position indicator, for showing position of doors, moving cars, etc.; light intensity meter, for measuring intensity of light for photography; scanning material to detect flaws or defects: ultra-violet ray meter, for recording the intensity of ultra-violet light; instrument for ascertaining fog height, used with a captive balloon in determining fog height necessary for safe aeroplane height.