Radio mirror (Jan-Oct 1923)

14 RADIO DIGEST June g, 1923 1 GOOD PORTABLE SET HOOK-UP \'hSl OR 4^2 V fOliVJD-N ORUV-199 22!iVT045V FOR the fan who contemplates building a very compact portable set the hookup shown as R.D.-84 is recommended. Any of the tubes with low current consumption can be used. Naturally the proper rheostat to be used will depend on the tube and the source of filament current. The antenna circuit includes a variometer and a .001 mfd. veriner variable condenser in series. These two controls of wave length will permit extreme selectivity. The regenerative feature of the circuit guarantees plenty of volume in reception. The circuit is an adaption of the Colpitts transmitting circuit named the "Gibbons." If desired audio frequency amplification can be added in the usual manner. The plate voltage need not be more than 45 and in fact 22% volts will do in most cases. This depends on the tube. Since maximum results are expected, good apparatus should be used and care taken in assembly and wiring. Soldering joints should be properly made. Spaghetti insulation should be used in all compact sets thus reducing the possibility of short circuits to a minimum. As a portable set, U.V.-199 or W.D.-ll tubes are convenient. The latter can be lighted by a single dry cell and the former needs only a large, tubular flashlight cell (yielding 4% volts). The tube sockets should be mounted on sponge rubber or heavy felt batting to eliminate vibrations that breaks the filament, and microphonic tube noises when the set is in use. Short flexible leads to the socket and thence to the regular bus bar wiring will also aid in stopping these shocks. FIRST STEPS IN RADIO (Continued from page 11) the potential between adjacent turns use is made of bank winding. In a 2-bank winding the turns are laid on as numbered in the illustration. Two turns are first put on the tube, the third jumps back on top as shown, the fourth turn, coming back to the tube and the fifth goes back alongside the third and so on. A 3-bank and a 4-bank are also shown. By this means the distributed capacity is reduced to a minimum and a compact coil results. Since this type of winding is not suitable to rnachine (or even hand!) winding the honeycomb and duo-lateral coil was devised. In this winding the turns are spaced some distance apart and cross each other at an angle. Since adjacent turns are well separated and the layers cross at an angle the distributed capacity is effectively kept down while a large inductance is obtained in a small space. Spider Wei) Winding' Instead of winding the turns of an inductance alongside of each other an attempt to wind them on top of one another in a flat spiral resulted in the spider web or staggered coil. Originally this form of winding consisted of a round wood form in which was inserted an uneven number of wood pegs or sticks. The wire was woven around the sticks to form a thin flat winding very suitable for use in tuners using a tickler coil inductively coupled to the secondary of a receiving set. The more modern spider web differs only in that a slotted form is used as a form for winding. Another form of winding that is seldom used but possesses many advantages is the torroidal coil. In this form of inductance the coil is wound on a doughnut Figure 22— Showing How Torroidal Coils Are Wound like form cut from wood as shown in Figure 22. It will be seen that the magnetic field is completed within the coil and such a coil will not act inductively upon another winding. This is a great advantage in some cases particularly where feedbacks in a set causes trouble. Thus this winding would be suitable for tuned Radio frequency amplifiers or for single circuit circuit tuners where inductive feed-back is not employed. Variometer Effect So far we have considered industries that are variable only by tapping the winding at fixed places. In the variometer. however, we have an inductance that can be varied in minute steps. The principle of this instrument is shown in Figure 23. The rotor and stator are represented by straight tubes for the sake of clearness. When the windings are connected in series the same current flows through both coils. In a properly designed variometer the magnetic fields of the stator and rotor are of equal strength. When the rotor is in such a position that its poles are similar to those of the stator (or so their fields Figure 23 — How the Variometer Functions assist each other) the inductance value is at a maximum as will be seen from the illustration where the two fields act together. As the rotor is turned its field does not coincide with the stator field and the mutual inductance is decreased, reducing the total inductance proportionately. When a full half turn is made the fields from the two coils are in opposition and neutralize each other thus reducing the inductance to a minimum. Therefore, it is possible to vary the inductance very gradually for fine tuning. In order to obtain a wide range of tuning it is necessary to have the minimum value of inductance as near zero as possible. For this reason the stator winding should come very close to the rotor so that the neutralization of the fields will be more nearly complete. In practice, about the greatest range is to reduce the inductance value to one-fifth of maximum value. In the next chapter, "Tuners and How to Tune Your Set," we will take up the application of these inductances in the various tuning circuits. (TO BE CONTINUED.) To thoroughly understand the workings of triode tubes, the beginner should read a book on the subject. ADJUSTABLE COIL MOUNTINGS FOR FLEWELLING CIRCUiT Triple Coil Mounting $5.00 List Double Coil Mountings 3.50 List A patented feature locks the coil in place and prevents the coil from being thrown out of adjustment once station is tuned in. Equipped with a' silver finished calibrated dial. Licensed under U. S. De Forest Pat. 1365170 Dealers special write for discounts ASTORLOID MFG. CO., IVtfe #?: Review of Books Ideas for the Radio Experimenter's laboratory. By M. B. Sleeper. The novice will find a wealth of information which will assist him in the designing, constructing and testing his set. Data on laboratory instruments are given. Price, 75 cents. Experimental Wireless Stations. By P. B. Edelman. Simple directions are given in this book for making Radio equipment for the transmission of messages over long distances. Price, $3. Vacuum Tube Receivers. By O. F. Heslar. A book that tells how to make a simple set. How to make a cabinet. It includes a 27 by 36-inch layout blue print. Price, 75 cents. The Armstrong" Super-Regenerative Circuit. By George J. Eltz., Jr., E. E. This is a De Luxe edition of this famous circuit. Profusedly illustrated and fully explained. Fifty-two pages. Price, $1. How to Retail Radio. A new book telling of tested plans and methods and policies for the dealer in Radio. Financing, location, store equipment and arrangement. Price, $2. Radio rirst Aid. Illustrated with working drawings and complete data as to the necessary equipment and cost of constructing from the simplest to the most modern Radio outfits at home. Price, $1. Home Radio — How to Make It. By A. Hyatt Verrill. This book is particularly adapted for the amateur who desires to know how to make Radiophones. Twelve full page illustrations and diagrams. Price, 75 cents. Radio for the Amateur. By A. H. Packer and R. R. Haugh. The underlying principles of Radio thoroughly explained in simple language and understandable illustrations. This book will teach you how to construct and operate a receiving' set successfully.. Price, $1.50. The Radio Amateur's Handbook. By A. Frederick Collins. A new revised edition (T *% GOLD-GRAIN CRYSTAL DETECTORS DEALERS— NewLi8t Attractive Discounts 123 WMadixon Jt.Chicaqo of this book is just out. It m complete, authentic and informative work on Radio. Fully illustrated. Price, $1.50. Ideas for the Radio Experimenter's Laboratory. By M. B. Sleeper. This book tells in a simple way the how and why of Radio apparatus. Comprehensive data is given on such necessary laboratory instruments as the oscillator, wavemeter, direction finder, Radio compass, vacuum tube characteristic measuring set and detailed advice given on the winding of various kinds of standard inductance coils. Price, 75 cents. The book department of the Radio Digest is prepared to send you any of the books on Radio published, whether listed in our Book Review or not. Let us know what book you want, send us your check and we will see that the book is mailed to you. Postage stamps in payment for books not accepted. Send money order or check. Radio Book Department, Radio Digest, 123 W. Madison St., Chicag-o, HI. We Live In Kansas —but we receive programs from Atlanta, Minneapolis, Davenport, Fort Worth, Madison, Los Angeles, Dallas, Kansas City, St. Louis, Denver and San Antonio on Crystal without batteries. Your crystal Bet requires only easy inexpensive changes. Send stamp for further information or $1.00 for copyrighted drawings and instructions. Everything explained. Satisfaction guaranteed. LEON LAMBERT, SOI South VoluUia, Wiohita, Kansas At Last! You Can Buy a Real lVa-Volt Clear Tube The W. D. 12's only Competitor. Functions at 1 to 1.1 Volts. Genuine Platinum Coated Filament. Fits Standard Socket Do not confuse this tube with common Silvered Tubes advertised as 1%-Volt. Detector — Amplifier Absolutely Guaranteed $4.50 MAIL ORDERS FILLED PROMPTLY Cash or Money Order (No Stamps) Dealers write for Quantity Discount TREXO TRADING CO. 200 Broadway (Suite 210), N. Y. City femoattt >-w Radio Head Sets ifti <s* V1' Increase the Receiver's Efficiency & The high efficiency, wide distance-range and perfect clearness of Federal Standard Head Sets are the logical result of 22 years' experience in the making of precision communication apparatus. Federal Standard Head Sets are nationally endorsed by experts. Use them and get PROFESSIONAL efficiency from your radio. Federal makes a complete line of radio apparatus. Write for descriptive literature and price. For sale by leading dealers Federal Telephone and Telegraph Company BUFFALO, NEW YORK Western District Office: 417 South Dearborn St., Chicago, III. Federal Standard Head Sets are made with 2200 Ohms and 3200 Ohms resistance.