Projection engineering (Sept 1929-Nov 1930)

Page 52 Projection Engineering, September, 1929 maximum capacity of 250 watts. It is provided with a long shaft and special bracket, so as to be mounted clear of the panel for proper air circulation, or again for mounting on thick slate panel. Ideal as a heavy-duty line control, variable speed motor control, plate voltage control for transmitters, field control for shunt type generator, and so on. Finished in nickel. Mica and asbestos insulation. Handy bakelite knob. Sturdy and wearproof. NEW PHOTOPHONE EQUIPMENT A new sound installation designed for theatres up to 500 seats capacity and to cost not more than $2,995 installed will soon be placed on the market by RCAPhotophone. The new model will be a dual-system unit, for reproduction of both disc and sound-on-film recording. NEW MAGNAVOX X-CORE SPEAKERS The X-Core marks a further improvement in Magnavox Speakers. It is a very definite refinement and one that provides a positive alignment of the moving coil in the air gap. There are two main divisions of the speaker assembly. The cone head and the field coil frame assembly. The cone bead includes the cone housing, the paper, cone, the moving coil and the X-Core. The field coil frame assembly includes the field coil, the heavy steel case enclosing the field coil, the main core, the input transformer and the speaker base. The moving coil, or driving unit is rigidly and directly attached to the cone, and delicately suspended in the strong magnetic field produced by the field coil and transmitted by the steel case and the cores. Bakelite, proved to be the best because of its durability aud its resilience, is used to suspend the moving coil. This coil is fastened to the cone with a special cement and rigidly clamped with the aluminum retaining ring. The flexible moving coil leads are completely insulated and very sturdy. The air gap in which the moving coil oscillates is between the X-Core and the outer pole and as the X-Core is pressed into a bearing in the outer pole the air gap must be always uniform. This construction simplifies conehead ajpemblies, as the X-Core is included in tire conehead and the screw connecting the main cone and the X-Core is used only to hold the two in magnetic contact. It is evident that coneheads can be replaced with absolutely no danger of the coil rubbing in the gap. It is a distinct advantage to have the conehead removable. It facilitates assembly as well as it does replacement or repair. This is an exclusive Magnavox feature, and with the development of the X-Core makes it absolutely positive and sturdy. POWRAD CONDENSERS Powrad, Inc., of Brooklyn, New York, are marketing a complete line of by-pass and filter condenser blocks housed in metal cans with mounting and soldering lugs both in standard blocks and to manufacturers' specifications. These condensers are conservatively rated and guaranteed in capacity from — 5% to +15%. A unique method of impregnation acquired through six years' of skill and experience in the manufacture of paper condensers have led to the production of an exceedingly rugged product noted for its remarkable working strength and high insulation resistance. Powrad non-inductive filter condenser. POWERIZER AMPLIFIER RACKS AND CONTROL PANELS Amplifier racks and control panel equipment for centralized use in theatres, schools, auditoriums, stadiums and other places where music or voice is to be "piped" over large areas, has just been introduced by the Radio Receptor Coznpany of New York City. This equipment is of the panel or vertical rack type, although made up essentially of the well-known powerizer units. In the case of the two-channel assembly, it stands 6 feet high by 20 inches wide, comprises six panels, and weighs 200 pounds complete. The two-channel amplifier assembly, which is certain to be the most popular for most installations, comprises a PXP-250 powerizer, made up of two units, for each channel. Thus the panel assemblv represents a monitoring loudspeaker and distortion meter for the top panel ; a switch and pilot light for the PXP-250 or power output unit, representing the second panel : a switch and pilot light for the voltage amplifier or PXP-171 unit, representing the third panel ; the fourth panel contains the main switch and throw-over switch from one channel to the other, the a-c field switch for the dynamic speakers and a throwover input switch from synchronous to non-synchronous : the fifth contains the second PXP171 powerizer and its switch : and the sixth contains the PXP-250 and its switch. The assembly is so arranged that -:■:::-.■...■.--■ ■■■■.-:■. -A iiiiiiiillllillliiiiiiiiiiiinii iiiiiiiii:iiii!iii[iii!i[iiiiiiiiiiiiiiiiui milium Right: New Powerizer twochannel amplifier, containing a distortion meter, a monitor ing loud-speaker and all the necessary control equipment. any of the complete units with panel may be removed and another unit substituted, such as a monitor, or a radio set with amplifier and microphone panel, which, of course, would take care of the microphone meter and switch. The power units are the standard powerizers arranged for bracket mounting. All audio wiring Is carefully shielded so that these units are found very quiet in operation. WRIGHT-DE COSTER DYNAMIC REPRODUCERS Wright-DeCoster, Inc., of St. Paul. Minnare in production on their new dynamic reproducer. The field coil of this dynamic speaker contains nearly fifteen pounds of wire, which, in combination with an extremely Wright-De Coster dynamic speaker chassis, low reluctance magnetic path provides a high degree of efficiency. Notwithstanding the fact that only nine watts are necessary for field excitation, and the air gap is somewhat larger than standard practice, there is sufficient sensitivity to produce an output, on a single 171-type power tube which is usually possible only with a 210-type tube. The unit will stand exceptionally high powers, having been used successfully on amplifiers supplying as high as 45 watts of speech energy. Due to special construction of the voice coil, there is little possibility of voltage breakdown between layers. There is usually no equalizer or cut-off filter necessary except on an amplifier in which there is a prevalence of harmonics of very bad wavelength distortion. Prices on the speakers range from $52 to $100, with and without cabinets and in both 6-volt d-c. and 110-volt a-c. types. WRIGHT-DE COSTER TONE MODULATOR Wright-DeCoster, Inc., of St. Paul, Minn., have also introduced a new Tone Modulator which is employed for increasing or decreasing the high and middle registers of Details of the Magnavox X Core Speaker, a recent new development.