International projectionist (Jan-Dec 1947)

' jh^KUhiUh^H ^^^^^^Fs^^H POWER ^Bfr '" 'w 1 I ; Kg) orr . TRIATIC m m "; '•' ■Ml ° !' ' " * * p O.^. / ' CAPACITY i ho 80 f i O ' 1 | I °UTPUI -' +90 V. HB f ■* *^ '" n -yrV » QJ ';•• *'* © J PROBE GAIN input A ■^^w Extreme compactness, largely made possible by the development of miniature tubes, marks the RCA Triatic Signal Tracer. it will be indicated as follows: (1) Positive d.c. voltage: eye will open (shadow angle increases) . If the probe is removed from contact with the circuit being checked, the eye will return to its original position. The time taken for this return will be an indication of the voltage at the test point — the longer this time, -the higher the voltage. (2) Negative d.c. voltage: eye will ■close (shadow angle decreases, edges may overlap). Return time after removing test probe from centering is indication of the voltage at the test point. (3) A.C. voltage: the eye will open and close rapidly, producing a blurred image. Except at low voltages, the width ■of this blur will not indicate the amount of voltage present. Power line a.c. will, of course, have a constant voltage; audio frequency signal will fluctuate thus producing a flickering shadow. Using Probe Circuit in Conjunction with Audio Amplifier When extremely low a.c. voltages are to be located with the probe circuit, it will be necessary to amplify them. In this case the signal tracing probe lead is connected to the amplifier input jack, and the amplifier output connected to the probe jack. The gain control of the audio amplifier is set approximately onequarter open as a preliminary adjustment and thereafter regulated as required. The presence of a.c. voltage on the probe will be indicated by a rapid opening and closing of the electron eye, re sulting in the shaded or blurred edges of the image. Since some hum voltage will be picked up by the exposed probe tip, the amplifier gain control should be kept at the lowest possible setting that will give an adequate indication on the electron eye. The presence and amount of any such hum voltage can be determined by grounding the probe tip on the instrument case while watching the electron eye. The change, if any, in eye deflection will indicate the amount of stray voltage. Measuring Capacitance The selector switch is set to one of the three capacitor test positions, low. medium or high. The low range is for capacitors from ten micro-micro-farads (0.000010) to 8000 micro-micro farads (0.008 mfd.) ; the medium range from 0.001 to 0.8 micro-farads, and the high range from 0.1 micro-farad to 80 microfarads. The capacitor to be checked is con nected to the tip jacks located on the front panel. The capacitor measuring bridge is balanced by rotating the large knob until the electron eye shadow is at maximum opening. The unknown capacitance will then be indicated by the position of the pointer on the scale which corresponds to the setting of the range switch. A high power factor, or leaky capacitor, will produce a blurring of the edges of the electron eye shadow at balance of the bridge. The poorer the capacitor, the greater the blurring. Miscellaneous Application To use the Triatic Signal Tracer as a photoelectric cell supply, connect the case of the signal tracer to the negative side of the phototube circuit and conneot the anode side of the photocell to the +90-volt tip jack located on the front of the panel. This circuit will supply a well filtered d.c. potential of approximately 85 volts to one photocell, or (Continued on page 33) Historical Development of Sound Film By E. I. SPONABLE Twentieth Century-Fox Film Corporation V. DEVELOPMENT OF SOUND EQUIPMENT BY FOX-CASE CORPORATION SPONABLE surveyed the Fox West Coast studios October-November 1927 with a view to converting them for sound work, and drew up designs for the first unit. The building of these studios was held up by Fox, owing — among other reasons — to the estimated cost of $250,000 being too high. In November 1927 Case suggested "noise reduction" in an affidavit dated November 28, 1927, quoted below: "It is of great advantage when photo graphing sound-on-film to have the ground noise level as low as possible between words or sounds when there is nothing on the film in the form of modulation to cover up the ground noise. A method of doing this has suggested itself to my mind as follows : If the recording light which itself is modulated or by another method is modulated mechanically is only eliminated while modulation is not going on in the circuit, this would mean that when no modulation is present the light would be reduced to a minimum automatically or might even be put out entirely. "This would mean that between modulation or between words or between sounds the negative sound record would be unexposed or white upon development. This, on the positive, would be reversed or black, thereby reducing any ground noise that there might be between words or sounds. The method of accomplishing this could be the same as is at present used in the transoceanic telephony where it is essential that automatically t J. Soc. Mot. Pict. Eng., May, 1947, p. 407. only one sending station is in operation. "As soon as active modulation ceases in one direction and starts in the other direction, the modulation passing in the circuit actuates a relay mechanism to instantly put into action this sending station. In other words, in our simple modulation circuit any alternating or pulsating currents would actuate a mechanism to bring the recording bight up to the brilliancy desired for the best operation of the system and while no modulation was passing, the light would automatically be reduced to the point where no record would appear on the film. "This is signed and witnessed at 9:40 A.M., November 28, 1927 and I am now going to call up Dr. McKenzie at the Western Electric Company and inform him of this idea so that it can be put into operation, if they so desire, on their mechanical method of recording sound." /s/ Theodore W. Case During the last of 1927 and the first (Continued on page 30) ; INTERNATIONAL PROJECTIONIST • November 1947 23