Radio age (Jan-Dec 1925)

56 RADIO AGE for December, 1925 The Magazine, of the Hour for if our I & battery eliminator REX answers the eliminator i, problem. The B Batteryeliminator equipped with Magnatron Rex tubes works day in and day out . — ■ silently and economically. MagnatronRex is the product of long research by the oldest exclusive manufacturers of thermionic valves in the country. It has been designed primarily and only for eliminator work. Magnatron and Excellence have come to mean one and the same thing. Impartial laboratories and radio engineers throughout the country have certified this. Their reports explain why Magnatrons in your set will make it function better. Your dealer has the Rex as well as the other Magnatrons. Ask him today! They list for only $2.50. Write for your FREE copy of "Pot Pourrt . — ■ a snappy review of mirth and music \ to Dept.A , Connewey Electric Laboratories, Magnatron Building, Hobo\en, 7s[ew Jersey. West Coast supfliedjrom complete stocks carried by PACIFIC RADIO LABORATORIES 256 So. Los Angeles St. Los Angeles, Calif. Dealers — if you want the best products, the fastest shipments and the most liberal discounts, write on your letterhead for our catalog L1003. Wakem£M?Laugh' FKEE -STAMPS 616 beautiful copper etched American, Canadian, and European stamps, each with the call letters of a station, FREE with Ideal 48-page Radio Stamp Album and Log. Also contains complete list of stations both alphabetically and by call letters. As you hear new stations, just put the proper stamps in your album. Album and stamps become a permanent and interesting record of the stations you receive. Tou and your children will enjoy it. Complete album, 8"xll", heavy board covers, SI plus postage. SendhMoney Just pay postman after album and stamps arrive. We prepay postage if you prefer to pay with order. MONEY REFUNDED if not DELIGHTED. Send order today— NOW. Postal will do. IDEAL CO.. Dept. 2029, 366 Wrigley Bldg. Chicago RADIO AGE ¥ Tuning Your Radio By Chart Curves (Continued from page 21) lengths as follows: Take a sheet of paper eleven inches square. Rule off a one-inch margin on the lower and left-hand edges, and in the larger space draw faint intersecting lines a half inch apart, as in Figs. 1 and 2. Number the bottom horizontal line 0, the one-inch line above it 10, the two-inch line 20, and so on up to and including 100 to correspond with the numbers on the tuning dials. Now number the lefthand vertical line 200, the one-inch line to the right 240, and two inch line 280, and so on up to 600, to cover the meter wavelength range of the broadcast receiver. Suppose the first station recorded has a wavelength of 326, and the dial settings which brought it in are 32, 30 and 28 for dials No. 1, 2 and 3 respectively. Take a rule and place it parallel to the vertical lines so as to pass through a point on the lower line between the 320 and 360 points, which will coincide with the 326 meter position. Place dots at the edge of the rule at the dial positions 32, 30 and 28. These dial positions are found by consulting the dial position figures in the left hand margin of the paper; after finding the line marked 30, the location of dial positions 32 and 28 can be estimated. The Dial Settings IN a similar way, make dots representing the dial settings of three or four other stations whose wavelengths range up to 550. Some way of distinguishing the dots should be employed such as marking the dial No. 1 dots red, the dial No. 2 dots blue, and the dial No. 3 dots black. Now draw a smooth curve line passing through all of the dial No. 1 dots. Draw a similar line passing through the dial No. 2 dots, and a third passing through the dial No. 3 dots. With these three curves drawn, it is a simple matter to bring in any station whose wavelength is known. For instance, if the desired station has a wavelength of 400 meters, lay the ruler down on the curve chart on the vertical 400 meter line. The points on the horizontal lines at which the ruler intersects the three curves will indicate the positions to which the dials must be turned in order to bring in the desired station by means of this home-made curve chart. Thus the radio fan who desires to tune in various stations, whose wavelengths are known, can do so conveniently by preparing a curve chart for his particular set. The next set which we will discuss is the super-heterodyne, which is one of the most complicated sets in its mechanical construction but is one of the easiest to operate. There are usually three controls, one of which is for adjustment of the battery current to the vacuum tubes. This adjustment should be made as usual. In this case use a low setting to start with. The other two controls serve to select the stations, one of them tuning the loop circuit while the other tunes what is called a "driver" or "oscillator." These sets are usually designed so that when signals are to be received the positions of the two selectors will be very nearly but not quite the same. The principle on which this set operates is that the frequency of the "driver" (Turn to page 58) Tested and Approved