Radio today (Jan-Mar 1939)

slightly, thereby giving expression to the speech. The sounds created electrically are reproduced over a sound system. While the Voder was built primarily as a demonstration device for the Golden Gate Exposition and N. Y. Worlds Fair, it may have practical uses in providing sound effects. The imitation of a train and the bellowing of a calf are but two of its unlimited sound possibilities. To the radioman this invention should be most significant, for it shows that not only can man reproduce actual sounds, but also that man can artificially create them. As some see it, the Voder foreshadows many of the future possibilities of (radio) tube operated devices. TEMPERATURE VERSUS RESISTOR SIZE AND MOUNTING The determination of the physical dimensions of a resistor to fit a particular application ordinarily involves the consideration of three factors: wattage to be dissipated, maximum temperature allowable, and mounting conditions; plus the consideration of certain graphical data, states the engineering department of Ohmite Mfg. Co. The actual wattage to be dissipated in the resistor is first calculated by means of any of the variations of Ohm's Law such as, Watts =z I2R, where I is the current in amperes and R the resistance in ohms. Next, the maximum temperature which the resistor can be allowed to attain is stipulated. This temperature is generally below the maximum (450° F. above the ambient or room temperature) which is allowed by the N. E. M. A. standards for vitreous enameled resistors. The presence of other nearby equipment often necessitates much lower temperatures. j APPROXIMATE TEMPERATURE RISE OF VITREOUS ENAMELED ^RESISTORS VERSUS CORE WATT RATING (SIZE) IS*1?/ J 00 — — TSL" 0 2', MULTIPLY ACTUAL WATTS BY ABOVE NUMBERS TO OBTAIN NOMINAL CORE WATT RATING. The third step is to consider the mounting conditions of the resistor, i.e., whether the unit is mounted in free air (the basis of the nominal resistor rating) or mounted enclosed so that air circulation is restricted. A reference to the graph illustrated herewith will now tie these three factors together with the graphical data (based on observations of typical re QetThii 80-P<Lqe£o*k Tells Everything About True Dynamic Testing Ordinarily when you buy a piece of test equipment you use it for months before you know what it will do for you. This means you must first make the investment BEFORE you find out if it is profitable. But not so with the Rider Chanalystl We want you to know exactly what this instrument can do for you and how you operate it. We want you to be sure it's a good investment — BEFORE you buy it. So. we have prepared an 80-page (8V2"x 11") book, loaded it with illustrations and written it so you can understand ALL about the Rider Chana You Don't Need An Expert to demonstrate this easy to operate, trouble-shooting instrument. Read this book — go to your Jobbers and lyst and true dynamic and functional testing the first time you read it. This book with hard covers would ordinarily sell for $2.50. We will mail it to you for 25 cents in stamps or coin — a fraction of its preparation cost. We do this for we believe a serviceman should have the real facts on what he can expect of an instrument BEFORE he buys it. We know you will want a Chanalyst after you read this book. Send for it today) Mail only 4>0 FoJy^^s *o\v, Demonstrate It to Yourself / 5sjr?*«i*i*^ coioj Y°rk City The HIDER __ Chanalyst SERVICE INSTRUMENTS, Inc. 404 Fourth Ave ., New York City January, 1939 41