International projectionist (Jan-Dec 1947)

TEST EQUIPMENT FOR THEATRES (Continued from page 14) from reaching the volume control or the grid of the first tube; the input connection can, therefore, be attached directly to the amplifier plate circuit. An output jack, capacitively coupled to the plate of the output tube, facilitates the use of headphones if desired. Power is supplied by a built-in power supply operating from the 120-volt, 60-cycle A. C. line. A jack on the front panel is connected, through a resistor-capacitor filter, to the integral power supply, and will supply anode voltage to one or two photocells'. This voltage may be connected, by the simple throwing of a toggle switch, through a 1-megohm coupling resistor to the amplifier input jack. This connection permits the amplifier to operate directly from a photocell without any other electrical connections whatever. Manifold Tests Possible These features permit the use of this device for many tests, such as: (1) Focusing optical systems, adjusting lateral guide rollers, or balancing push-pull photocells on one sound head while the other is in normal operation ; (2) Checking one sound head for proper operation, normal photocell output quality, film, exciter lamp, and photocell defects, hum or vibration pickup, etc., while the other sound head is in normal operation ; (3) Stage by stage tracing to locate sources of noise, distortion, intermittent operation, or low gain; (4) Testing auxiliary devices, such as microphones, phonograph pickups, etc., for normal operation; (5) An emergency substitute for the normal photocell anode supply, and the first stages of theatre sound systems, in which failure has occurred; (6) Talk-back from stage to projection room when installing equipment (when used with a microphone) ; (7) In conjunction with a photocell, to find out whether room illumination supply is D.C. or A.C. (With a photocell and test lamp, to determine whether an unknown power source is D.C. or A.C.) If A.C, hum will be heard from the loudspeaker; if D.C, no hum will be heard, but clicks may be produced by interrupting the light which falls on the photoelectric cell. The Triatic Signal Tracer also includes a circuit probe tester incorporating a resistor-capacitor circuit and the electron-ray tube 6U5/6G5. This circuit provides a means of rapidly checking an amplifier or similar circuit to determine the approximate voltages present, their polarity, and whether they are direct or alternating. Only one range is needed, which is not subject to burnout or damage on voltages ordinarily found in an audio-frequency amplifier. This range extends approximately from 2 to 500 volts. D.C. voltages are indicated by the opening or closing of the electron-ray tube shadow, depending on polarity; the voltage is estimated by noting the time taken (after the probe has been removed from the circuit being tested) for the resistor-capac.tor to discharge enough to allow the electron-ray tube shadow to return to its normal position. This is accurate enough for rapidly checking circuits in case of trouble, when it is merely necessary to determine whether or not the voltage present is somewhere near its normal magnitude. The alternating-voltage indication is a blurring of the edges of the electronray tube shadow, the result of the rapid opening and closing produced by the applied alternating voltage. Since alternating voltage cannot charge up resistor-capacitor circuits to any permanent value, voltages are indicated by the width of the blurred area. All necessary cables, plugs, and cords are furnished with this equipment. These are placed in space provided in the bottom of the cabinet. In addition, a bracket is provided on the back of the special VoltOhmyst for carrying its own plug leads. . . . To Help You Give The Best Show In Town In DeVRY's new Theater Projectors — incorporating both picture mechanism and soundhead in one single unit — you get the wealth of knowledge and experience gained in the vast laboratory of war production. You get design refinements, resulting in simplicity of mechanism and elimination of unnecessary parts — to make maintenance economical and servicing easy. You need to see them in action to realize the rocksteady, flicker-free screening of the new DeVRYS ... the high fidelity of their true HEADQUARTERS FOR DRIVE-IN THEATER 5 TIME WINNER DcVRY alone has been, awarded five consecutive Army-Navy "£V for Excellence in the production ^SS§H "' Motion Picture Sound Equip to-life sound, from the softest whisper and the warmest tone to the weirdest shriek or the roar of a mighty organ. ... No perceptible flutter, hum or wow! Top-flight performance for either black-and-white newsreel or Technicolor feature. Priced to enable any theater to afford NEW equipment. DeVRY's famed ' G-T projectors now available Its war contracts completed, DeVRY's famed "G-l" Projector is now in production — quickly available. Before you buy projection equipment, mail coupon to DeVRY. PROJECTION AND SOUND EOUIPMENT. DeVRY CORPORATION, Dept. 1P-D2 1111 Armitage Ave.. Chicago 14. Illinois Please send details about the NEW DeVry 35mm Theater Projectors . . . Amplifiers and Speaker Systems. Name Address Capacity INTERNATIONAL PROJECTIONIST February 1947 25