Projection engineering (Jan-Dec 1931)

Page 24 PROJECTION ENGINEERING New Developments n d News of the Industry ELECTRAD AMPLIFIERS When measured by the multiplicity of its uses and advantages, no other development of modern times compares with the power amplifier. First produced as a radio accessory, it has outgrown radio by leaps and bounds, and now occupies a distinct field of its own. Wherever sizable audiences must be reached, wherever widely distributed oral communications or musical entertainment are desired, the poweramplifier, with its accessory equipment, wipes out distance and provides the outlying listeners with a front-row seat. Electrad amplifiers are distinctive because of their simplicity, compactness, higher gain and great distortionless output with a minimum of input voltage. The LoftinWhite direct-coupled circuit is used, which requires fewer parts and yet performs more efficiently, with finer quality of reproduction. Electrad, Inc., 175 Varick Street, New York, has a new bulletin describing this new line. ▲ CARBON SAVINGS Examine the stubs in the carbon waste can in your projection room! Compare them with a full length carbon! Then look at your carbon bill ! Each stub can be burned down to a two inch stub with the GoldE 30 per cent carbon saver. The projectionist merely inserts the burnt end of the carbon stub in the saver, twists it into the taper, self tightening thread, locks it with the anchor screw, rolls on a flat surface for trueing. When carbon burning time is noted the stubs can be so graded as to make their use economical to the last degree. NEW DISC RECORDS A new method of recording by means of which twice as much music can be put on a phonograph disc as formerly was announced in August by the Durium Products Corporation. Described as the greatest development in recording since the introduction of the electrical system, the new process, known as the Micro-Channel process, will permit the playing of an entire piece of concert music without touching the phonograph to change the record. The improvement is effected by reducing the thickness of the walls between the needle grooves. Records manufactured by this method are made of Durium, a synthetic resin which is extremely tough and at the same time flexible. Special fibre board is coated with a shell of Durium five one-thousandths of an inch thick, on which the recording is made. The finished record can be scaled across the room, placed flat on the floor and hammered, or bent almost without injury. Because of the durability of Durium, the needle grooves are placed very close together, with twice as many grooves or channels to the inch as in ordinary records. Exhaustive tests show that notwithstanding the reduced wall thickness they can be played about three times as often as the old-style record. The first commercial application of the new method will be a standard-sized disc containing five minutes of music, or twice the capacity of the ordinary record. DUBILIER TUBULAR PAPER CONDENSERS In keeping with the trend towards individual condensers inserted in the pointto-point wiring, in place of expensive condenser blocks in cans, the Dubilier Condenser Corporation, 4377 Bronx Boulevard, New York City, announces a new line of tubular paper condensers. The Dubilier Type 706 is an outside wound or non-inductive standard paper section wound on the standard mandrel and surrounded by several turns of heavy craft paper. Pigtail leads permit of ready wiring in any circuit. The tightly wound paper covering provides ample mechanical and dielectric strength. An attractive label is printed on the paper wrapping. Among the outstanding features of the new unit are extreme compactness and convenience. The unit represents solid condenser in the absence of a can or container. Due to thorough impregnation of the completely wound section and its cover, together with the special means whereby the paper wrapping shrinks tightly over the section, the resultant unit is fully protected against moisture and mechanical effects. The leads are securely held in place and cannot be pulled loose without destroying the condenser. The ends are fully insulated, so that only the leads themselves present "live" parts. Dubilier 706 units are available in various capacities from .0001 to J^ mfd., and in d-c. working voltages from 200 to 600 volts. CRYSTAL CUTTING HEAD A cutting nead particularly suited for recording metal records is announced by the Astatic Microphone Laboratory, Youngstown, O. The cutter uses a Rochelle Salts crystal as the driving element. The frequency response of the cutter is unusual, increasing with frequency. Almost any desired response may be obtained by simple electrical networks. The impedance of the cutter is quite high and may be coupled directly to the plate of the power tube without matching. The action of the crystal in the circuit is much the same as a good condenser. Other applications of these crystals include microphones, phonograph pickups, loudspeakers and as drivingelements in oscillographs. CELL COUPLING CABLE G-M Laboratories, Inc., 1735 Belmont Ave., Chicago, announce the perfection of a new cell coupling cable for use in sound equipment. This cable has five times the capacity reactance of standard microphone cable so frequently used in sound equipment, and in addition, is highly nonmicrophonic. The use of this cable reduces the attenuation of high frequencies, eliminating to a large degree the frequency discrimination of most photoelectric cell amplifiers. This results in increased brilliance of reproduction of voice and instrumental music, so noticeably lacking in many typei of sound equipment. Those interested in this cable may obtain information by asking for G-M bulletin No. 134. RCA-PHOTOPHONE, INC. With the initial manufacturing order for 500 units of special size sound reproducing equipment being rapidly absorbed by the unprecedented demand from exhibitors in both domestic and foreign fields, E. O. Heyl, vice-president and general sales manager of RCA Photophone, Inc., announces a duplication of the first manufacturing order to take care of the requirements of the commercial and foreign departments for the remainder of the year. "We had no idea that our initial order would be absorbed so quickly," said Mr. Heyl, "but immediately after we announced the introduction of our new all a-c. operated special size equipment for theatres up to 500 seating capacity, the response was quite surprising. While we are making installations in many new theatres and in some that had not as yet given up their silent apparatus, the majority of our installations are replacements. The small exhibitor realizes that he no longer can attract patrons to his theatre unless he can guarantee satsfactory sound and our new special size apparatus is designed expressly to meet his requirements. "