Radio Digest (July 1924-Apr 1925)

April 4, 19Z5 RADIO DIGES T— Illustrated 17 A. B. C. Course in Radio Fundamentals Chapter II— The Electrical Circuit By David Penn Moreton THE path in which electricity moves is called the electrical circuit, and it is necessary to have a clear understandingof the fundamental properties of electrical circuits and the various quantities associated with them in order to get a clear understanding of the operation of the many different electrical circuits found in a Radio set. The electrical circuits found in a Radio are of numerous forms, but they all possess, to a very great degree, the same general properties and involve the same quantities. For example, the filament circuit of an ordinary vacuum tube, as shown in figure 4. This circuit is quite typical of all electrical circuits. It contains a source of electrical energy — the storage battery — an energy transforming device — the filament where electrical energy is transformed into heat energy; and the necessary connecting wires. It must be remembered at all times that the electrical circuit is closed on itself and like the circumference of a circle, it has no beginning nor end. When there is a movement of electricity 4. ///2 w — ^ //<y / ) s \ r 'p a? k> / Figure 4 in an electrical circuit, there is said to be a current of electricity in the circuit. The exact nature of electricty is not known, yet the laws governing its action under definite conditions are quite well known, just as the laws of gravitation are known, yet we do not know the constitution of gravity. The laws which explain the operation of the majority of electrical circuits are very similar to the laws which explain the flow of a liquid in a line of pipe or hydraulic circuit. On account of the similarity of the two circuits, and Figure 5 also on account of the laws governing the operation of the ordinary hydraulic circuit being quite obvious, simple hydraulic analogies will be used to illustrate what is supposed to be taking place in the electrical circuit. Direct Current Flow When the movement of electricity in the electrical circuit is in one direction there is said to be a direct current in the circuit. Such a current is produced by a battery or direct-current generator. When the movement of electricity is alternately in opposite .directions, there is said to be an alternating current in the circuit. The laws governing the alternating current are quite different than the iaws for the direct current. The discussion in this chapter will be confined to direct currents and the alternating current and its laws will be discussed later! According to the electron theory of electricity there is a movement of something in the electrical circuit, yet this movement is not identical to the movement of a liquid in the hydraulic circuit. The electron theory will be discussed later. The flow of water in a hydraulic circuit is usually expressed as so many gallons per minute, so many cubic feet per second, or any combination of volume and time units. The movement or flow of electricity in an electrical circuit is likewise expressed as so many units of quantity of electricity in a unit of time. The unit of quantity of electricity is called the coulomb. When there is a uniform flow of electricity of one coulomb through an electrical circuit in each second, there This New Super-Horn Ready to attach instantly— adjustable to any set, controlling accurately the volume of sound. possible by quantity production. At All Good Dealers ">(ot Merely a Loud Speaker" Brings Magic Clearness to Radio THE new Kellogg Symphony Reproducer is a new-type horn recently developed by our experts — based on the magnetic diaphragm principle. It brings to radio a marvelous tone-quality, a beauty you have never heard before. Attaches to any set and can be adjusted for the particular "volume" requirements of the set. At all radio dealers. Ask for it by name. See it, hear it — compare ! KELLOGG SWITCHBOARD & SUPPLY CO. CHICAGO, ILLINOIS Kellogg Symphony Reproducer With every Kellogg Radio part, the Use is the Test is said to be a unit of current of electricity in the circuit. This uniform rate of movement of electricity of one coulomb in each second is called an ampere. Resistance in Circuits The movement of a liquid through a pipe is opposed by a certain amount of opposition or resistance. Likewise there is a certain amount of opposition offered by the electrical circuit to the free movement of electricity around the circuit, and this opposition is called the resistance of the circuit and it is measured in a unit called the ohm. The resistance offered by vari Figure 6 ous materials to the passage of electricity through them varies between wide limits. Those materials which offer a relatively low resistance, such as the metals, are called conductors; while those materials which offer a comparatively high resistance, such as glass, rubber, bakelite, porcelain, dry paper, etc., are called insulators. The terms conductor and insulator are only relative, as all materials will Collapsible Standard of the Radio Industry Loop Aerials The only loops of their kind sold at popular prices. Built by radio engineers — electrically and mechanically correct — beautifully finished and sturdy. A touch and and a new station comes in — or one is cut out. Their selectivity is remarkable. And remember that Lincoln Loops sell at moderate prices. No other loops of their kind or efficiency sell at these low prices. Lincoln 4-point Tapped Loop Built for any circuit where it is desired to vary the inductance of the loop. Exceptionally fine for super-heterodynes. Lincoln Center-Tapped Loop $6.50 For any set employing radio frequency amplification. For certain Superheterodynes requiring a center tap. Write to Lincoln If your dealer cannot supply you, order direct giving your dealer's name. Lincoln Loops are fully guaranteed. Send for literature. We welcome correspondence with legitimate dealers and jobbers. Lincoln Radio Corporation 224 North Wells Street CHICAGO conduct to some degree even though they are called insulators. The electrical pressure — sometimes called the electro-motive force, electricity moving force, voltage or drop in potential — causes the electricity to move in the electrical circuit when the circuit is closed. The electrical pressure is measured in a unit called the volt. There are a number of different ways of producing an electrical pressure, but the two most common methods are by chemical action in the battery and by electromagnetic induction in the generator, both of which will be described later. Many years ago a scientist by the name of Ohm experimentally discovered that there was a definite relation between the resistance of an electrical circuit, the (Continued on page 20) . i i in ■■■ ii i r~r"~rr^>i " FIVE TUBES TWO DIALCONTROL SIMPLICITY, elimination of intricate operation is the great demand of radio users. Radio has graduated into an established industry where users do not expect to know the technical working of radio apparatus any more than they do an automobile, but do demand' perfection in entertainment, consistent operation and comfortable simplicity in selecting and tuning in stations. Meco Radio Receivers answer these new standards as well as the old ones of selectivity, range, volume and clarity of tone. The ideal of immediate entertainment and simplicity of operation, is now perfected in Meco Receivers. 1 Five tubes held under perfect control with only Two Dial s — one dial eliminated. 7 Only one dial to log — the ■^ wave length tuning dial. Meco Radio Receivers have tuned radio frequency action with two stages of radio frequency, and two stages of audio amplification, one detector. The Meco Console Meco Receivers are produced in two models. The cabinet model shown above, retailing at $100 and the Console model in period design, entirely self contained, shown below. You can examine Meco radio receivers at your dealers or he can supply you from recognized radio jobbers. Metropolitan Electric Company Des Moines, Iowa