The motion picture projectionist (Nov 1929-Oct 1930)

42 Motion Picture Projectionist August, 1930 Hints on Equipment Maintenance BECAUSE of the rapid advances, amplifiers today are intricate. Consequently, when troubles occur, they require the services of competent trained projectionists and engineers. Good, reliable test equipment is necessary. In almost every projection room, where sound equipment is installed, there will be found a portable direct current voltmeter and ammeter, which is usually found in the ERPi spare parts cabinet. Any measuring instrument will stand a certain amount of abuse; however, it is advisable to see that they have reasonable care to assure the highest degree of accuracy. Nc matter what the value of the testing instrument may be, it should always be put away in some' location that is free from dust, oil, heat, moisture and excessive vibrations. Projectionists often leave expensive testing instruments in a rewind bench drawer among other things including tools. A container should be provided for testing instruments, which are not in use. There is positively no excuse for the projectionist or engineer abusing testing instruments. Storage "B" Batteries Many of the first Western Electric sound installations are still receiving their plate potential from storage "B" batteries. Storage "B" batteries consist of twenty-four cells. Each cell delivers a potential of two volts and each group of cells deliver, when fully charged, forty-eight volts. The storage "B" battery often becomes unusable owing to one or more cells becoming defective. In such cases, the defective cell can be shunted out by connecting together the two cells on either side of the defective one. This method, of course, decreases the total output of the battery by two volts. Such an emergency method of repair will be satisfactory until the defective cell is replaced with a new one. A defective cell can usually be located by using a voltmeter; every good cell will cause the needle to deflect, but a dead cell will, of course, not cause a deflection. Handling Head Sets Every Western Electric sound installation includes a head set, which is used for testing. Dropping or jarring them tends to destroy the molecular arrangement in the magnet core, with the result that it may become slightly demagnetized. The screw cap on each phone must be kept tight, or rattling and distortion may be the result. Constant use often tends to loosen the caps, so that it is well to examine them periodically. If it is necessary to remove the cap and the diaphragm from the phone units, when installing a new cord, or for any other reason, the cap should be unscrewed carefully and the diaphragm slid off from the magnets, instead of pulled off. Pulling the thin diaphragm off is likely to bend it and then it will not work well, making replacement necessary. Noisy Reproduction On a few occasions, crackling noises in an amplifier have come from a defective resistor. Western Electric amplifiers have many resistors for a certain definite fixed resistance. A defective resistor can be located with a head set, with a "C" battery connected in series. Noisy reproduction is the most common of all complaints with sound reproducing equipments. During long experience with sound reproducing systems 70 per cent of all troubles fall fundamentally into the noise category. It has been found that the noise problems are the most baffling of all to projectionists and servicemen. Noises in amplifiers usually occur during the performance and they are hard to find. Noise can emanate from so many different sources. Sporadic hissing, crackling and frying noises are usually caused by short circuits developing in vacuum tubes. Moon accessories are standard projection room equipment MOON Wall -Type Speed Indicator Fits all Makes Warranted accurate and absolutely dependable at all times. Get one for your room Wall-Type Indicator for Simplex Other Moon Products: Film Measuring Machine De Luxe Speed Indicator Special Powers Speed Indicator Film Mending Machine Moon Auto Rewind All kinds of projection accessories Write for catalogue MOON M. P. ACCESSORIES CO. 222 So. Hamel Drive Beverly Hills Calif.