Projection engineering (Jan-Dec 1931)

Page 20 PROJECTION ENGINEERING 262. Should all m.g. sets be grounded, and, if so, why? 263. How should the commutator be kept clean? 264. How tight should the brush tension be on the commutator? 265. What will cause a bearing to run hot? 266. When would you consider a m.g. set to be heating excessively? 267. How do you replace old brushes and fit the new ones to the curvature of the commutator? 268. Give two or more reasons why brushes on a m.g. set will spark. 269. What are the causes for brushes sparking, and what are the remedies? 270. What is a motor generator? 271. What is meant by the armature? 272. Give the chief causes which will make your motor generator vibrate. 273. What is a transformer? 274. Give some of the advantages of mazda equipment. 275. What will cause the bulbs to blacken, and what is the reason for the height of the glass bulb? 276. What is a prismatic condensor? 277. When using a prismatic condensor, will the condensor be closer to the aperture than if you use a piano condensor ? 278. Using a small diameter projection lens, which condensor combination (prismatic or piano convex) will allow more light through the lens? 279. Can a prismatic condensor be used when running slides ? 280. Describe how to start a mazda lamp in operation, and tell what happens at each step. 281. How close should revolving shutters be to end of lens barrel? 282. What would you use for a focussing card on a projector with a rear shutter ? 283. Show how you would adjust the lamp and mirror to get a correct focus. 284. Give approximate distance between (a) center of mirror and filament, (b) filament and condensor, (c) condensor and aperture, (d) lens and revolving shutter. 285. When using a cinephor condensor system, is accuracy in the focal distance of much importance, and why? 286. What is the mirror image, and where should it be focussed? 287. What is meant by filament image ? 288. How many filament coils has a mazda lamp ? 289. When the mirror image is not properly focussed, what will be the appearance of the light on the screen? 290. Can a cracked mirror be used pn mazda? What will the effect be on the screen? Can a cracked condensor be used? 291. How can you overload a mazda lamp, and will you derive any benefit from so doing? 292. What will usually result from overloading a mazda lamp ? 293. What is meant by the term "sound picture" ? 294. At what speed must a sound picture be projected to get correct reproduction ? 295. What results are apparent in the reproduction when the projector is run at a lower speed? 296. What results are apparent in the reproduction when the projector is run at a higher speed? 297. How can the speed of the projector be varied on Western Electric or Northern Electric equipment? 298. At what speed does the turntable revolve? 299. Define a sound track film. 300. Define a disc film. 301. Why does the needle on the disc record travel from the center of the disc to the outside? 302. On the Vitaphone disc, is the actual sound record on the bottom of the track or groove, or is it cut into the walls of the groove? 303. What is meant by "drift" of the reproducer arm, and why is it used? 304. What might happen if the clamping weight is not secured on the disc, and the projector is in motion? 305. What is the "mechanical filter" on synchronous sound equipment? 306. What usually results from turntables not being level ? 307. How often should a disc be used? 308. What is meant by a scratch filter? 309. What is surface noise? 310. How often should a disc be cleaned, and what should be used? 311. How often should a needle be used? 312. Suppose the needle continually jumps out of the groove, and on putting on a new disc the jumping continues, what would cause this, and how could you remedy it ? 313. What effect on reproduction may a warped disc have? 314. How and where should discs be stored in the projection room? 315. How could you test a disc for warpage ? 316. What should you do with a disc that is badly scratched? 317. On disc film, what is the "start mark"? 318. Why is the "start mark" used? 319. On disc film, why is each foot marked on the side of the film? 320. Define "footage marks". 321. Of what help to projectionists are the "footage marks" ? 322. Do Technicolor films have footage marks? 323. Suppose you were projecting a Technicolor print and the film broke, piled up at the upper sprocket, and due to the brittleness of Technicolor was badly broken up, how could you put it in synchronism again? 324. Define synchronism. 325. What type of film must be used to replace any film removed, due to breaks, or for any other reason ? 326. Tell how to splice a sound track film. 327. Which of the lines, the white or dark ones, make the actual sound from the film ? 328. What is the difference between "variable area" and "variable density"? 329. What film producers use "variable density"? 330. What density does R.C.A. use in recording? 331. What is known as "motor-boating" ? 2,2,2. What is the cause of motorboating ? 22,3 How can "motor-boating" be overcome ? 334. What effect on reproduction may a poorly made sound track splice have? 335 Why should a sound track splice be painted out? 336. What causes surface noises on sound track film? 33J. How should sound track film be cleaned? 338. What effect may a heavy scratch on the sound track have on the sound reproduction? 339. What effect may oil on the sound track have? 340. What type of paint should be used on sound track splices, and why? 341. How could you tell if any footage had been cut from a disc film if it suddenly went out of synchronism ? 342. How would you proceed to restore it to sychronism ? 343. Is the start mark on disc film of any importance ? 344. What are storage batteries used for? 345. What apparatus do the "H" batteries supply with current on Western Electric or Northern Electric equipment? 346. What tubes do the "F" batteries supply ? 347. What tubes do the dry "B" batteries supply? 348. What bad effect will a defective "B" battery have on sound reproduction? 349. How often should wet batteries be charged? 350. How can you tell when batteries need re-charging? 351. What is "specific gravity"? 352. What is the use of a hydrometer? 353. What is "electrolyte" in storage batteries ? 354. What may happen if there is dirt or water on battery tops ? (To be concluded in July issue)