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Show k s s s i (Billed by Q. Douglas Wardrop. Editor of Radio Merchandising;.) The greatest thrill that a radio fan can get is to bring in a distant station sta-tion on a set that he built himself. This thrill Is greater if the set can run circles around any other set as far as selectivity Is concerned. The purpose of this article Is, therefore, there-fore, to bring before the fans a concise con-cise description of a set that is easily constructed at home and that will give satisfaction as far as distance and selectivity se-lectivity are concerned. In addition the volume this particular set delivers is something to marvel at. Most of the equipment for the set will probably be found in the fan workshops. work-shops. If not then the money in- L.f '.- -.- G : j rfss rai L --.--'-a ondttd ' pJgJt r, ? . "-. ! C"- - - a Meiinrorof f J 83iem6fy' Wtrrfjjc and shaft constuctton I I X 1 How the Windings Are Placed on Stator and Rotor. vested In the following parts will not be ill spent : One composition tube 4 Inches In diameter by 2 Inches wide. One composition tube Inches In diameter by 1 Inch wide. One composition tube 4 Inches In diameter by 1 Inch wide. One composition tube 3 Inches In diameter by 2 Inches wide. One .001 mfd. variable condenser. Vernier If possible. One .0005 mfd. variable condenser. Vernier If possible. One .00025 mfd. fixed condenser. One vacuum tube, preferably a UV200, but any tube will work. One rheostat to fit tube. One socket to fit tube. One grid leak, 2 meg. One one-quarter pound spool of No. 26 S. C. C. wire. Seven binding posts. One 7 by 12 inch panel. Four dials. Four 2 Inch lengths of -brass tubing tub-ing Vi inch in diameter. Strip of 5-10-lnch brass. One 2-foot length of flexible wire for pigtail connections. 'Phones, batteries and some small nuts and bolts. The first step In construction Is the winding and assembling of the coils. Upon the largest tube, 4 by 2 inch, 40 turns are wound in this manner. man-ner. At the extreme edge of tube 4ssmbr cf Ouprrs fit t Showing Details of Couplers and Shaft Arrangement. the wire Is fastened and 20 turns are wound on. The exact center of the tube Is then found and a space of 8-82 Inch on either side of this middle mark is left. The wire is then carried car-ried over this space and the winding wind-ing continued for another 20 turns, which will give 40 turns on the tube, going in the same direction and with a space of B-16 Inch left between each 20 turns In the center of the tube. This Is for the primary. The Secondary Tube. The next tube to be wound Is the 8 by 1 Inch tube. This tube Is wound with 20 turns In all with the same spacing as the above tube has In the center, namely 6-16 Inch. This Is for The 4 by 1 Inch tube Is then wound with 20 turns and the S-16 inch spacing spac-ing in the center is again carefully adhered to. Tills is also for the secondary. sec-ondary. The last tube, 8 by 2 Inch, Is wound with 40 turns with the space In the center left as per usual. This last winding is for the tickler. Fig. 1 shows the winding and spacing. spac-ing. The 4 by 2 inch col! and the 8 by 1 inch coll form one pair of windings. The 4 by 1 Inch tube and the 3 by 2 Inch tube form the second pair, that Is, the second half of the secondary and the tickler. The larger tube In each pair Is called the outside tube or the stator and the smaller tube Is called the Inside tube or the rotor. In the exact center of each tube a quarter-Inch hole much be drilled through both sides. These two holes are for the shaft of the rotor and should therefore be directly opposite one another. The brass strip Is now preparer! to become part of the set. First a 4-lnch piece of It Is cut Ttrnn, referring to Fig. 2, it Is bent In the shape shown on the stator coll. A hole Is then drilled In each eDd for use In securing the couplers to the panel. In the center of the strip a H-Inch hole is drilled for the shaft to go through. At a distance '4 Inch above and below this hole two small holes are drilled for fastening fas-tening the strip to the tube. The tube Is also drilled for the fastening i bolts. The next step Is to cut two strips j of brass 1V4 inches long and cut a: 'A-inch hole In the center, un either; side, that is above and below It, n small hole Is drilled for fastening.' This strip Is then placed inside of the secondary coll, 3 by 1, and formed to fit the Inside of the tube as! shown In Fig. 1. The remaining 7 Inches of strip j Is prepared In the same manner as; the one above with the exception of forming the last two strips which are: formed inside the 3 by 2 Inch tube-Instead tube-Instead of the 3H by 1 Inch tube. Each tube Is then drilled for the fas-, tenlng bolts. In Fig. 2 the couplers are shown, assembled. To do this it is necessary neces-sary to first put on the brass strip that holds the stator coll to the panel. Then the strips tlnat go inside of: the rotor tubes are fastened to their, respective tubes. The first rotor shaft Is the rear, one. This is placed In the proper position, and with about a half inclv extending from the outside of the stator. The brass tube and the brass strip Inside the tubing are soldered together. The other shafting is then placed-In placed-In its position. The most practical manner man-ner to do this Is to place the coupler on a panel and measure the distance the rod must project from the panel to take the dials used. Then solder the rod and the strip together. The Pigtail Connections. Next In line comes the pigtail connections. con-nections. These are shown In Fig.' 2. Four 6-inch lengths of the flexible flex-ible wire are cut from the original: piece and two pieces are nsed for each coupler. Two pieces are forced through each, brass tube and the ends are soldered' to the ends of the rotor winding. The other ends of the pigtail connections-are connections-are used to connect the rotor to the external circuit. The panel layout of the set should have the couplers at the top of the1 panel and the condensers underneath the couplers. Each condenser Is underneath un-derneath the coupler it controls. The primary coupler will, of course, go at the left edge of the panel so as to be near the aerial and ground posts. In tuning the set It Is well that you-do you-do not condemn It too soon, as Its- iir fr J i 1 jl 6 . 6- 6 I Diagram of Connections to Be Used With Selective Receiver. extreme selectivity Is often discouraging discour-aging until one becomes familiar with! the tuning tricks. It is possible to use regular varlo-couplers varlo-couplers In this circuit, but the results re-sults will not be as good. The con- densers should also be of the best.' If dry cell tubes are to be used ex-i perlment with the plate voltage until I you have found the best point. Shielding will sometimes aid If any capacity effects are noted; -the sec--ondary condenser will probably be the one needing the shield. The tickler-control tickler-control Is very critical and should be; watched carefully In tuning distant stations. It may be set at the bestj point for a certain band of frequen-j cles, but when a station Is received,! there Is. a possibility of losing It lfi the tickler Is turned too quickly. New! York Globe. |