International projectionist (Jan-Dec 1940)

This department is a collection of random thoughts and some not so random; fact, fancy and opinion relating to the man behind the man behind the gun — the serviceman. The prime purpose of this section is to promote a closer relationship between serviceman and projectionist based on a better understanding of their mutual problems through an exchange of news and views, kinks and kicks. To this end, contributions relative to any phase of the serviceman's activities are invited. IN many of the larger rooms where the rewind table is located at the further end of the room, the projectionist finds it difficult to check the arcs without leaving the rewind, and frequently this has to be done at the wrong time when checking film. A simple warning signal can be made attached to the relay armature of the arc control. Drill a small hole in the end of the armature where the contacts are located and insert in this hole a clapper from a cheap electric bell; then mount the bell adjacent to the clapper so that on the movement of the armature the bell will be struck. This can be arranged so that the bell will be struck when the carbons are either too far apart or too close, whichever is desired. Or, two different size bells can be mounted so that the two tones can be med for close or open warnings. — H. R. Davidson, RCA, Atlanta, Ga. • • • In case of a lower failure where an Erpi 12-B rectifier is in use, the power supply switch on the unit should be immediately turned to either "off'' or "1" position and not turned to the "2" position until the 314-A tube has warmed up after the power is restored. The use of a "No-Voltage Release" type magnetic contactor is recommended where power supply conditions result in extreme variations and frequent failure of supply voltage. — C. J. Faulstich, RCA, Jacksonville, Fla. • • • In projection rooms where local house phones are used, it is possible to automatically cut off the monitor when phone is used by bringing one side of the monitor voice line to phone and connect contactor in series with same. The contact "make" and "break" is actuated by the receiver hook. — H. E. Frisbee, RCA, Pittsburgh, Pa. • • • The old tough job of using sandpaper and time to seat motor brushes of a motorgenerator set can be eliminated by using a compound called "Brush Seater," obtainable from the Ideal Commutator Dresser Co., 1251 Park Ave., Sycamore, 111., or their distributors. This compound comes in a block 4%"xl%"x%", and can be cut to the size of a brush. The method of using on W.E. m. — g. Erpi sets has been as follows: Install brushes on one side and insert brushseater up each brush holder on other side. Hold seater material against commutator until it starts to cut. Then remove brushes and clean. Repeat on opposite side. The seater compound will not stick to metal. This method is quick and makes a beautiful job on the brushes. After brushes are seated in this method, no arcing or noise has been found to ensue. — H. M. Madison, RCA, Hollywood, Calif. • • • To repair a broken flexible motor coupling, obtain a piece of high-pressure hose with a Vn" hole in it, with four or five layers of fabric moulded in the rubber (this hose used on high-pressure sprayers for citrous trees) and cut a piece the length of the coupling. This is pushed on the motor shaft and soundhead shaft and clamped with proper size hose clamps. This makes for a very neat job and a perfect emergency coupling. — C. L. Swinney, RCA, Atlanta, Ga. • • • A case was recently encountered where uneven take-up action was corrected by using sandpaper to improve the seating of the fibre disc. This was done by removing the take-up and inserting a circle of sandpaper, cut slightly larger than the friction surfaces, between the fibre disc and the adjoining clutch face. The pulley was then rotated by hand, causing the sandpaper to remove all high spots from the fibre and forming a perfect seat. — J. D. Steely, RCA, Pittsburgh, Pa. • • • Western Electric 702 and 705-type fadera can be made to operate very smoothly and quickly by bending up the detent roller arm so it does not contact the detent plate. As the roller arm is not electrically connected, contact resistance will not be affected. — H. I. Huutgren, RCA, Springfield, Mass. • • • Persistent "speeding" of KS-motors which do not respond to the usual treatment of commutators and brushes, may be due to trouble in the 709-C control cabinet. A quick check can be made by measuring the voltage between terminals 3 and 4 on the 709-C with the motor running. If the voltage is less than 100, look to the 29.5 mfd. capacitor, trouble with which may be breakdown of the case. In looking for background noises and interference in sound systems, don't overlook the arc feed control motors. Even modern D.C. lamps are sometimes guilty, if brushes or commutators be neglected. — K. P. Haywood, RCA, Pittsburgh, Pa. • • • If a hum should develop in an equipment using a TA-7276 power unit, due to a partially defective filter condenser in a p.e.c amplifier or 41 amplifier circuit, and no spare is available, the filter condenser in the speaker circuit can be interchanged with the condenser in the amplifier circuit temporarily. The defective condenser will cause far less hum in this part of the equipment, and an emergency may be thus alleviated. — S. B. Epstein, RCA, San Francisco. • • • In the KS-5161 type motors, the oil hole in the front bearing is several inches from the hole in the protecting screen mesh. The difficulty of oiling this bearing without spilling it over the outside can be overcome by first placing a soda fountain straw through the screen into the bearing oil hole and dropping oil down the straw. — W. J. Strieby, RCA, Hazelton, Pa. • • • Every once in a while a sound system failure is encountered which apparently clears itself within a short time. Often amplifier filter condensers are suspected, that is, the possibility of short-circuited condensers healing themselves after the amplifier has been turned off. Here is a good way to check filter condensers in such instances: Remove all tubes except the rectifier tube. Then turn on the amplifier for several seconds, resulting in the filter condensers being subjected to a higher than normal potential. If one is weak, it will probably break down; it can then be detected and replaced. The reason for the higher than normal potential, of course, is that the removal of the other tubes also removes the load these tubes normally impose on the rectifier and filter bank; consequently the potential goes up. Caution: apply this test for only a few seconds, because there is no sense in subjecting the filter condensers to excessive voltage any longer than necessary. — L. J. Patton, Altec, N. Y. City. • • • Here's another stunt to remember. I NOVEMBER 1940 33