International projectionist (Jan-Dec 1947)

successive cycles, the algebraic average value of which is not zero. A pulsating current is equivalent to the sum of an alternating and a direct current. Rectifier: A device having an asymmetrical conduction characteristic which is used for the conversion of an alternating current into a pulsating current. Such devices include vacuumtube rectifiers, gas rectifiers, oxide rectifiers, electrolytic rectifiers, etc. Reflex Circuit Arrangement: One in which the signal is amplified, both before and after detection, in the same amplifier tube or tubes. Regeneration: The process by which a part of the output power of an amplifying device reacts upon the input circuit in such a manner as to reinforce the initial power, thereby increasing the amplification. (Sometimes called "feedback" or "reaction.") Screen Grid: A grid placed between a control grid and an anode, and maintained at a fixed positive potential, for the purpose of reducing the electrostatic influence of the anode in the space between the screen grid and the cathode. Secondary Emission: Electron emission under the influence of electron or ion bombardment. Sensitivity of a Phototube: The electrical current response of a phototube, with no impedance in its external circuit, to a specified amount and kind of light. It is usually expressed in terms of the current for a given radiant flux, or for a given luminous flux. In general, the sensitivity depends upon the tube voltage, flux intensity, and spectral distribution of the flux. Static Sensitivity of a Phototube: The direct current response of a phototube to a light flux of specified value. Superheterodyne Reception: Superheterodyne reception is a method of reception in which the received voltage is combined with the voltage from a local oscillator and converted into voltage of an intermediate frequency which is usually amplified and then detected to reproduce the original signal wave. (This is sometimes called double detection or supersonic reception.) _ Television: The electrical transmission of a succession of images and their reception in such a way as to give a substantially continuous renroduction of the object or scene before the eye of a distant observer. Tetrode: A type of thermionic tube containing a plate, a cathode, and two additional electrodes. (Ordinarily the two additional electrodes are of the nature of grids.) Thermionic Emission: Electron or ion emission under the influence of heat. Thermionic Tube: An electron tube in which the electron emission is produced by the heating of an electrode. Total Emission: The value of the current carried by electrons emitted from a cathode under the influence of a voltage such as will draw away all the electrons emitted. Transconductance: The ratio of the change in the current in the circuit of an electrode to the change in the voltage on another electrode, under the condition that all other voltages remain unchanged. Triode: A type of thermionic tube containing an anode, a cathode, and third electrode, in which the current flowing between the anode and the cathode may be controlled by the voltage between the third electrode and the cathode. Tuning": The adjustment of a circuit or system to secure optimum performance in relation to a frequency; commonly, the adjustment of a circuit or circuits of resonance. Vacuum Phototube: A type which is evacuated to such a degree that the residual gas plays a negligible part in its operation. Vacuum Tube: A device consisting of a number of electrodes contained within an evacuated enclosure. Vacuum-Tube Transmitter: A radio transmitter in which vacuum tubes are utilized to convert the applied electric power into radio-frequency power. Vacuum-Tube Voltmeter: A device utilizing the characteristics of a vacuum tube for measuring alternating voltages. Voltage Amplification: The ratio of the alternating voltage produced at the output terminals of an amplifier to the alternating voltage impressed at the input terminals. Capsule-Size RCA Phototube RCA's new electron tube, designated 1P42, is the smallest phototube ever offered commercially. About the size of a .22 calibre long rifle cartridge, it has a maximum diameter of only % inch and an overall length just under 1 13/32 inch. It is activated by light entering through a tiny window at its larger end. Comparing favorably with larger phototubes in sensitivity, the tiny new tube is expected to find many applications in business and industry, particularly in devices and machines where the size of former phototubes has been a problem. In multiple-circuit control devices, the new tube makes possible either smaller devices or more circuits in the same space. STRONG COPPER OXIDE AND TUBE TYPE RECTIFIERS L . A . The modern means as an ideal powe lamps. Low original, o costs. Quiet opera Distributed thro theatre supply de THE STRONC 87 City Park Av The World's La Project of converting A.C. to D.C ' supply for projection ar aerating and maintenanc tion. ugh leading independen criers. i ELECTRIC CORP e., Toledo 2, Ohi< rgesf Manufacturer o 'on Arc Lamps c e t > f MONTHLY CHAT (Continued from page 5) is required by law to display conspicuously a sign stating in large red letters the legally-imposed limit of occupancy. New York theatres, film and legitimate, were bagged via the strictest regulations imaginable many years ago. Iowa is admittedly in bad shape on this proposition, but it has company in several other states with deficient or no safety laws. It is ironic that a Labor organization, smeared with the "selfinterest" tag, has to fight this battle on behalf of the paying patrons of the world's fifth largest industry. Nor is it reasonable to expect that even a State Association can muster the strength to overcome the ignorance, the prejudices and the politicianing of a group of lawmakers. What is needed in such instances is the powerful pressure that can be exerted only by such organizations as the National Fire Prevention Association, the General Office of the I. A., and the Society of Motion Picture Engineers, all of which outfits have a vital stake in the establishment and maintenance of standards. The S. M. P. E. might be expected to respond to an appeal from Iowa projectionists with the same alacrity as it did to the recent suggestion that it acquaint exhibitors with recommended practices relating to equipment. Of course, politicians are immune to any amount of proof or persuasion that doesn't stem from an aroused public opinion. And molding public opinion is usually an expensive job, certainly beyond the resources of a small projectionist group. The fact that the Iowa boys seem destined to be knocked down for the fourth consecutive time in an unselfish effort to contribute something to the industry should lend emphasis to their poor-relation status in motion picture technological circles. Their cooperation is earnestly solicited in effecting "advances" in the art — provided some manufacturer is the beneficiary — but there is never an acknowledgment of their assistance when they need a lift. We repeat what we have reiterated through the years: projectionists should be banded together in their own national technological group which would ensure it a respectful hearing on all matters affecting the craft, whether it be a matter of state legislation, the correction of projection room defects, or the attempted imposition of any practice adversely affecting craft welfare. Prolonging Life of Pad Roller Arms For pad roller arms of Ml-1040 and similar soundheads using single rollers, periodic interchanging of upper and lower arms is suggested. These arms sometimes become sprung due to repeated lifting, by the outside end of the roller shaft, with a "heavy hand". However, they are sprung in an opposite manner; and periodic interchanging will generally be effective in maintaining the proper relation between sprocket and roller at both ends. 36 INTERNATIONAL PROJECTIONIST March 1947