Radio Digest (Apr 1925-Jan 1926)

20 RADIO DIGES T— Illustrated April 18, 1925 A. B. C. RADIO COURSE (Continued from page 19) value. The brushes are placed in such a position that they make contact with the segments connected to a particular loop while the loop is moving from a 45degree position on one side of a plane parallel to the magnetic field to a 45degree position on the other side of this plane. This results in the brushes changing from the segments connected to one loop to the segments connected to the other loop each 90 degrees that the loops rotate. The electrical pressure between the brushes will then have the form shown by the heavy line in figure 25. The variations in the pressure can be reduced by increasing the number of loops and segments in the commutator. The loops of wire and commutator correspond to what is called the armature of a generator. The magnetic field is usually produced by an electric current rather than by a permanent magnet. An armature of the type described above is called an open-circuit armature because the loops are only useful when the commutator segments of that loop are in contact with the brushes. When Fig-are 26 the loops of wire are all interconnected in such a manner that they are all useful in producing an electrical pressure the armature is called a closed-circuit armature. An armature of this kind with six loops or coils is shown in figure 26. In figure 26 the loops are wound around an iron ring which provides a mechanical support for them, and also a better conductor for the magnetic lines. An armature of this kind is usually called a ring armature. Most of the armatures are of what is called the drum type, that is, the winding is placed around an iron core which has a drum shape and both sides of each turn are on the outside of the drum. If a current be sent through an armature, like the one shown in figure 26, from an outside source, such as a storage battery, the armature will rotate in the magnetic field and the machine will be a motor. The direction of rotation of the armature of the motor will be opposite to what it was for the generator if the magnetic field and armature current COME TO THE Radio Exposition ST. PAULMINNEAPOLIS April 25th to May 2nd See and hear the latest in Radio Dance on America's greatest dance floor to the music of COON-SANDERS Original Kansas City Nighthawks and PAUL BIESE'S ChampionVictor Recording Orchestra The = Radio Exposition Company 1030 N. E. Marshall St. Minneapolis, Minn. are both in the same or both in the opposite directions for the motor to what they were for the generator. The left hand or motor rule may be used in determining this relation. This rule is applied in the same way as the generator rule except you use the left hand. (The alternating current circuit in regular electric machinery is analogous to that of Radio reception and its simple explanation relative to the electric dynamo will be easily understood by the beginner in Radio. — Editor's note.) HOW TO OPERATE SET (Continued from page 18) Antenna Compensator settings. The setting of the compensator which produces the highest reading on the Antenna Wave Length dial is the correct compensator setting for the antenna being used and will not need to be changed unless the receiver is used on a different antenna. It will not be necessary to adjust the antenna compensator again unless the antenna is changed. To tune the Federal 141 proceed as follows :_ First, set 4 so that pointer is at extreme right, 3 to the extreme left and 2 at about 10 on the dial. "With 1 at any point between 5 and 90, rotate 3 to the right until a click is heard in the phones or loud speaker. Turn 1 slowly until a station's carrier wave is accurately located. Turn 2 slowly until the click is heard again. This time the click will be followed instantly by the music or voice. Improvement in quality and volume, if necessary, may be obtained by accurately adjusting 1 and 2 by means of the verniers 1A and 2A and by carefully advancing 3 a trifle toward the right. A carrier wave is represented by a whistle. This whistle is not loud, but is distinct and will, as 1 is rotated, vary from a shrill note to a low weak tone and then back to the shrill note. Always stop the dial at that point where the whistle is lowest in tone; never in the shrill tones. The exact center of this low pitched tone is the correct position for 1. If a powerful station is near by, greater selectivity may be had by moving 4 toward the left and then tuning for the desired station. When operated as above, Federal Type 141 gives surprising results in distance, volume, selectivity and tone quality. By writing the .settings of Dials 1 and 2 on the log card which is furnished with the receiver, the corresponding stations may be tuned in again by returning The "Goode" Two-o-One A Le Ton d'argeat Postpaid QUARTER AMPERE AMPLIPIEB — DHTBCTO» RADIO TUBE GUARANTEED SATISFACTORY AH "GOODE" Tube* Sold Direct to the Consumer — No Dealer Profits ONE — "Goode" d»i jjq Detector-Amplifier v * «0»7 THREE — "Goode" e f\{\ Detector-Amplifiers O.UU (AH postage prepaid) The "Goode" Two-o-One A Tube itnplllos or detect!. It In a quarter ampere, Ire volti, standard bate flllvered tube. Mend express or postal money order — New York draft — or pergonal chock to — The Goode Tube Corporation Incorporated Owensboro (Dept. A) Kentucky the dials to these positions. In this case 3 should always be started at the left and rotated to the right until the desired volume is obained. Always make accurate adjustments with verniers 1A and 2A. (The radically different Super-Zenith VII will be presented next week with circuit diagram and photograph of the internal assembly. Correspondence from readers indicates unusual interest in this Zenith receiver which, due to its variable coupling radio frequency transformers, is a distinct advance in the progress of tuned radio frequency amplification. — Editor's Note.) FOUR FILTER SUPER (Continued from page 17) circuit jack, which is at the extreme right end of the panel. Test for Fixed Condenser Unfortunately, fixed condensers cannot well be tested while connected in the set, and to determine whether any of the condensers are defective it will be necessary to remove them from the receiver. To test fixed condensers after they are taken from the set it is only necessary to touch the two terminals from our battery and head phones to the two sides of the condenser and, if there is a "short" within the condenser, the same click will be produced as is noted when the two terminals are connected directly together. If the condenser is good, there will be a very faint click, but it may be readily distinguished from the strong click produced when the condenser is omitted from the circuit. Grid condensers may be tested while still in place in the set by removing the grid leak cartridge and touching one side of the test system to the G terminal on the socket and the other side to the condenser connection away from the socket. It is very easy to connect the oscillator coupler in such a way that oscillations are not produced, and one suggestion, if signals are not heard, is to carefully check the connections to this coupler to be very sure that the connection from the P terminal of the oscillator socket goes to the lower end of the center coil, the upper end of this center coi^ to go to the plus 45 B binding post. The lower end of the top coil should be connected to the rotor plates of the oscillator variable condenser and to the negative filament bus wire; the upper end of this top coil must be connected to the G terminal on the oscillator tube socket and to the stator plates of the condenser. It is conceivable, but not likely, that none of the 8 tubes London, Madrid Newcastle, Aberdeen— that'sjust a few of them AGAIN Elgin Super-Rein■L *-artz leads -all others! Every trans-Atlantic report investigated was found to be ABSOLUTELY authentic ! Many happy owners of Elgin sets again tuned in the European stations. ELGIN The Ford of Radio " will give you the selectivity and distance it has given others. And you can save $50.00. Let us tell you how — FREE Mail the coupon TODAY for the complete working drawings of the famous Elgin SuperReinartz, the set that gets the distant stations. They are free — no obligations, just a stamp for postage, please! tear out this coupon — „«•■ ■---■ s !"StndtVafon1f9«fS \ ■ S»»"VRe IT $0 00 orchis set. I en » ! Xse a SmP for Postage. , I close » J J I I Name I ■ I i AddreS8 ISZZ^m***^ J are ready oscillators on 45 volts, so if, after all other tests fail, oscillations are not produced, the upper end of the center coil should be disconnected from the plus 45 B binding post and connected to the plus 90 circuit. This can best be done by connecting it to the wire which goes down through hole 30 from the intermediate amplifier unit, at the point where this comes out on the underside of the sub base. That is the nearest point at which the plus 90 circuit comes to the oscillator coupler. Condenser Variations Most of the loops on the market are designed to work with .C005 mfd. variable condensers, but it may be that either the loop used has too many turns or the condenser is of slightly greater capacity than .0005. If either is the case, it will be found that KSD and KYW come in at about 80 on the loop dial, and if this proves to be so in actual use, the inner turn of the loop should be removed. This will bring the two stations mentioned at a higher point on the dial and will probably put them about where they should be, at 92 or 96 on the dial. If, on the other hand, the condenser is a little "light," that is, does not come up to full .0005 mfd. capacity or, if the loop does not have quite enough turns, it will be found that with the condenser at 100 on the dial you are unable to get above stations at 485 or 500 meters. If this proves to be the case, another turn should be added at the inner end of the loop, which will move stations down the dial and should bring in KYW and KSD. If one turn does not prove enough, a second turn should be wound at the center of the loop. The same facts apply to the oscillator grid coil and the oscillator variable condenser; if the higher wave length stations come in below 88 or 90 on the oscillator dial one or two turns should be removed from the grid coil of the oscillator coupler, which is topmost coil, while, if one is unable to get above 500 meters with the condenser at maximum setting, one or two more turns should be added to this top coil. If all variable condensers had exactly the same maximum capacity of .0005 this adjusting would not be necessary, but it happens to be the case that many condensers only go up to .00046 while many show, on test, a maximum capacity of .00053. fihwio* iundeisUndmdA iassembk cu-cuiisi iopetate sets &t f improve leceptiod §/, -"pHIS book, pre '/A '////, X pared by the i '//// technical staff of Vl/i II h Radio Digest, is l/lfi (m for the millions of S ml, listeners who want ////. U to know the what, '////. I whys and hows of '/m their receivers — 'M what is inside, llli why it is there, and I m how to operate it "Ij. for best results. '//// The New Badio Book is ///// given free with a year's 'ff/l. subscription to Badio Mj[, Digest. Tills wealth of WA information, carefully I , classified, can be yours 'ff/l 'ff/l within a few days if you ff/l, ffffi will use the coupon. Wit '////. m mi in in m. hi m 'in m in. mi 'III in, m Ilil RADIO DIGEST 510 N. Dearborn St., Chicago, III. 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