Showmen's Trade Review (Jan-Mar 1945)

38 S H O M E N • S TRADE R E V I E W January 6. 1945 ; mm _ How Condensers Are Constructed and Their Electrical Characteristics By Tom McNamara lATSE 505 When we immerse two pieces of aluminum in an electrolyte (a chemical decomposable by an electric current) and pass electric current from one plate (or piece of aluminum) through the solution to the other plate, we form a nonconducting film upon one of the plates. This film is formed on the positive or anode plate. This process is called "Forming the Condenser" and is similar to electro-plating. The purpose of this coating one of the plates (the positive or anode plate) with a non-conducting oxide or film is to insulate that plate so that current will not flow into it. This coating, or chemically constructed dielectric, is much thinner than the thinnest paper that can be obtained. The thickness of the dielectric in such condensers is of extreme importance, and by means of the electrolytic action whereby we create this type of insulation or dielectric for the anode plate, we are enabled to construct condensers for powerful amplifiers which are but a fraction of the size of the older type of such equipment. The development of the electrolytic condenser, as a matter of fact, has made possible the construction of midget radio receivers. Early types of these condensers used a liquid as the electrolyte — the liquid being placed Article l\o. 8 In Fundamentals Of Projection in an aluminum container with the anode centrally located within the container and totally surrounded by the liquid. Figure 1 is the symbol used in indicating an Electrolytic Condenser on a wiring diagram with the polarity of the connecting lines shown to assure proper hook up. Figure 2 shows the construction of an early type electrolytic condenser with the container (A) in direct contact with the liquid borax solution electrolyte (B) which completely surrounds the anode (C) except at the top where it is insulated from the container by a hard rubber, mica or fibre dielectric (D). The container (A) is the negative pole, and the anode (C) upon which the oxide forms extends up through the top of the condenser to provide the positive terminal (E). The anode in this type condenser is an accordionlike affair similar to the bellows of a camera, made of aluminum to provide maximum surface area in contact with the electrolyte within a limited space. The containers are constructed of copper or aluminum. Variation in Anode Design Figure 3 is another form of the Wet Electrolytic Condenser with the anode made of a long strip of aluminum folded back and forth as you might fold up a long strip of theatre tickets. In all other respects the two condensers are alike. Another newer form of electrolyte is the pasty or jelly compound placed in contact with the opposite side of a saturated gauze to establish an electrical contact. This latter type Dry Electrolytic Condenser (see figures 4 and 5) has the same electrical characteristics as the older type with the one advantage of being usable in any position since there is no liquid to spill out and can be smaller in size for comparable capacity with that of the liquid type. In Figure 4 we can see the composition of the dry electrolytic with the positive aluminum foil anode separated from the negative aluminum foil cathode by two jelly electrolyte saturated gauzes. Two additional gauzes are placed under the cathode in such a manner as to contact the other two gauzes thus completely enclosing the negative cathode and positive anode when the layers are rolled into a compact unit as shown in Figure 5. It can be easily seen that this dry electrolytic condenser requires much less space than the older type unit. From the above we can readily understand why it is important to observe correct polarity when connecting these condensers in a circuit as no oxide forms on the negative can or container. The electrolyte is at all times a fair conductor of electricity in either direction. The electrons cannot pass from the electrolyte through the oxide to the anode in sufficient numbers to be of any great concern, but, they can and will pass from the anode through the oxide to the electrolyte and thus spoil our condenser. However, if we are careful to connect our positive pole to the anode of the condensers this reverse flow of current will never occur, because electrons always flow from negative to positive and never in the reverse direction. Electrolytic Condensers have capacities that {Continued on Page 46) CA + CB + CC = C TOTAL C TOTAL CA CB CC NOTE FORMULAE APPLIES ONLY TO CONDENSERS OF EQUAL CAPACITIES