Radio Digest (July 1924-Apr 1925)

20 RADIO DIGES T— Illustrated January 31, 1925 DEMONSTRATING RADIO (Continued from page 17) phans towards sensitivity and quality. Their claim is that the tendency is too much towards sets of sensitivity and not towards sets that give outputs of really good tonal quality. reduce the voltage across the terminals of the output transformer so that the feedback will not be so strong. This resistance is variable, consequently, the amplifier may be adjusted for best reception. The theory of this amplifier is that the signals are first fed through push pull and then fed back, the tubes operating in parallel. i r J15-45VL ©A6V.© © "C" 0 OUTPUT 67-100 V. ©"B" ©" Tig-are 3 Figure 4 The filament arrangement, it will be noticed, is out of the ordinary. In the filament circuits, the tubes are connected in series in groups of two. This gives the same amperage through them, but requires a higher voltage across the A battery line. The total current draw for these six tubes is .18 amperes. Each tube requires across its filament terminals a drop of only 3 volts, but 3 volts of battery is not sufficient since the voltage of a cell diminishes with use. With tubes in series, and allowing 1 V2 volts for drop in the cells themselves, due to internal resistance and deterioration, the line voltage should be only 7% and only five cells, will be required. With the usual arrangement, to obtain the same battery life operating the same number of tubes, six dry cells are necessary. The series arrangement, then, results in a considerable gain in A battery economy. Storage Battery Pressure Another advantage of this filament arrangement is that a 6-volt storage battery may be used. When the battery is nearly discharged, the ouput may not have the desired volume, but 6 volts is permissible for a storage battery since there is not an appreciable dropping off in the terminal voltage due to internal resistance and deterioration of the battery. Storage batteries, as previously mentioned in this series, when fresh from the charger often test over 7 volts. There has been developed within the past few months an audio frequency amplifier from which good results may be obtained experimentally. It is shown in figure 3, except in this figure there is added a resistance Ri. Its function is to BLUEBIRD Radio Tubes Distinctly New AND EFFICIENT, satisfying every radio fan's wish in performance and price. Our direct sales plan enables U3 to sell at this low figure. "Bluebird" assures increased range and undistorted volume. Type 400 — 5 Volts. I Ampere Detector Tube Type 40IA — 5 Volts, .25 Ampere Amplifier and Detector Type 499 — 3-4 Volts, .06 Ampere Amplifier and Detector Type 499A— 3-4 Volts, .06 Ampere with Standard Base Amplifier and Detector. Type 412— P/2 Volts. .25 Ampere Platinum Filament Amplifier and Detector. All Standard Types . . .$2« TYPE 402 5 WATT TRANSMITTERS.. ..$3.00 EVERY TUBE GUARANTEED to work in Radio Frequency. Especially adapted for Neutrodyne, Reflex and Super-Heterodyne Sets. Shipped Parcel Post C. 0. D. When Ordering Mention Type BLUEBIRD TUBE CO. 200 Broadway NEW YORK CITY As usually operated, this amplifier is rather unstable. Vacuum tubes that are now on the market were originally designed for straight amplification only. There are a few Radio men in the country who have the apparatus for experimenting with vacuum tubes. In figure 4 is a hint. It is a push pull [ TRY US! I Radio Dealers! We are exclusive Radio Jobbers and DO NOT RETAIL, Howard — Crosley Liberty — Day-Fan Receiving Sets Complete line of parts. We Sell to Dealers Only. Write for Catalogl TAY SALES CO. 6 N.Franklin St., Chicago Index Your Set with RATA a© E EX NOTHING else lilce it. By writing in your dial readings, RADEX is automatically cross-indexed five ways. Lists every broadcasting station in the United States, Canada, Cuba and Mexico. Gives stations by cities, dial readings, wave length, frequency and call letters. Any station can be instantly referred to. Your set automatically calibrated by dial readings. Looks like a big dollar's worth — but sells for. a half. New 1925 edition now on sale at dealers or direct from us. Dealers and salesmen write for proposition THE RADEX PRESS 213 Euclid Arcade Annex CLEVELAND, O. tube. There are two plates and two grids, a pair on each side of the filament. The action during operation is merely to make the electronic flow shift from side to side. Connections to this tube are shown. Its double grid construction is not to be confused with that of the Solodyne tubes which were recently offered to the American public for the first time. (CONCLUSION) SIX TUBE HET-DUO-GEN (Continued from page 19) and on further stations, the points at which the stations will be found will be quite critical, and a vernier arrangement of some sort will be found to be an absolute necessity. As with other sets it will be a matter of patience and careful tuning to get your first list of stations logged, after which the others will be more easily located. The center dial is to be used as a volume control, turning the condenser towards the maximum position for more sensitivity and volume. The position of the primary coil of the filter, in its relation to the secondary coil, will have the following effects on the operation of the circuit: "When placed as close to the secondary as possible, the tuning on the dials will be somewhat less critical than when moved further away along the rod. In others words, the selectivity can be adjusted to your particular requirement, according to your distance from local stations. You will find that at each position in which you may try the primary coil, the setting of the special regeneration control condenser will have to be changed for best results in each position. When the primary winding is closely coupled to the secondary, more capacity is required to produce feedback to the oscillating point; while, when loosely coupled, or moved further away (with resulting sharper tuning), less capacity is needed. The sensitivity of the second detector is controlled by the amount of regeneration produced and, while not critical in adjustment, best re The Crystalstat The Ideal Reflex Detector but equally suitable for crystal sets The Crystalstat embodies the following features: A supersensitive crystal in an air tight enclosure. A brush cat whisker of gold tinsel strands. A micrometer adjustment by means of which the most delicate adjustment may be had. The multiple contacts of fine gold filaments prevent howling and gives light but sure contact. The crystal is our wonderful Star-ite, the pick of the Earth's best crystal. The Crystalstat attaches through one 5/16" hole in the panel so that only the control knob shows on the face of the panel. Packed in one dozen lots for dealers Ask your dealer to supply you or you may send for one C. O. D. with your money back if not completely satisfied. DEALERS and JOBBERS please get our catalog of crystals and detectors and our liberal distributing proposition. SPECIAL ^ INTRODUCTORY PRICE For a limited time only, and to introduce this new and superior Storage "B" Radio Battery to the Public, we are selling it for $3.50. Regular Retail Price is$5. 50. Yousave $2.00 by ordering NOW. A finer battery cannot be built than the World Storage "B" Battery (12 CELLS-24 VOLTS) To ten million homes with Radio Sets—and to countless millions of prospective buyers— this WORLD Storage **B" Battery brings a new coi caption of battery economy and perform, anee. Here is a battery that pays for itself in a few weekswill last for years and can be recharged at a negligible cost. And you. save $2.00 by ordering now. ASuperior Battery lS&liS&7U& Has heavy duty 2 1-8 in. x 1 In. x 1-4 In. plates and plenty of acid circulation. Extra heavy glass jars allow ready observation of charge and prevent leakage and seepage of current. It holds i is chance, while idly, at constant voltage. You will find this battery a boon to long distance reception. It. does away with a great many noiaea so often blamed on static " Mail your order today. SEND NO MONEY Just state number of batteries wanted and we will ship day order is received. EXTRA OFFER: 4 batteries In series 196 volts), $13.00. Pay Expressman after examining batteries. 5 per cent aiscount for cash lu full witb order. Send yoiir order NOW and save {2.00. WORLD BATTERY COMPANY A Maker* of the famous World Radio "A" Storage Batterp ^ 1219 S. Wabash Ave., Dept. 76 Chicago. IB. SAVE $2.00 BY ORDERING NOW! suits will be obained when working both detectors as near the oscillating point as possible. "When adjusting to this condition a distinct thud will be noted when the two tuning dials are rotated to a resonant point for a particular wave length. To use the third stage, move plug to last jack. No doubt you will immediately be greeted by a tremendous howl which is the result of overloading the third tube by reason of the three audio stages used. If so, to eliminate this howl, it is only necessary to adjust the high resistance unit at the right hand end of the sub-panel to the point where the howl disappears. (CONCLUSION) Antenna Circuit If your primary circuit does not tune sharply do not become discouraged, for this is due to the high resistance of the antenna circuit, and beyond making sure that you have a good ground connection, there is little that can be done about it. Wire for Various Uses Wire for winding inductances comes in many sizes and different insulations. There are single and double cotton-covered wires, usually listed as s.c.c. and d.c.c. respectively. And single and double silkcovered wires — s.s.c. and d.s.c. There is also a wire with an enamel covering. All of these wires may be used for coils, but with slightly different results. The size of the wire depends upon its use. In the wire guage that is used for copper wire, the higher the number the smaller the wire. For coils that are to be inserted in the aerial circuit, the size should be preferably between 18 and 22. In the secondary and other circuits, the' size may range from 20 to 26. Smaller wire than this would reduce the efficiency. ROICE Radio Tubes Economical and Powerful CUT your tube expenses In HALF. Here's "Roice," an efficient and durable tube that gives longer service and greater satisfaction. Powerful; increases range and volume with maximum clearness. We sell direct only. You save by this plan; that enables us to sell "Roice" at this low price. Type 00 — 5 Volts, I Ampere Detector Tube Type 0IA— 5 Volts, .25 Ampere Amplifier and Detector Type 99—3-4 Volts, .06 Ampere Amplifier and Detector Type 99A — 3-4 Volts, .06 Ampere with Standard Base Amplifier and Detector Type 12— I </2 Volts, .25 Ampere Platinum Filament Amplifier and Detector Shipped Parcel STAt"BD $Q50 Post C. O. D. TYPES £g Type 02 5-watt Transmitters, $3.00 All Tubes Guaranteed to give best results in Radio Frequency. Also for high-powered circuits such as Neutrodyne, Reflex and Super-heterodyne sets. When Ordering Mention Types ROICE TUBE CO. Newark, IT. 3". 21 Norwood St. Make BIG MONEY! ^-IN RADIO— ^ We Need Men— Can You Qualify? Ozarka representatives make real money because they give real values and deliver a real service. For instance, there is a4-tube Ozarka Instrument for loud speaker operation, giving wide range of reception at $39.50. Our men demonstrate Ozarka Instruments and Install. The Instrument makes the sale easy by its performance. We train you to know radio and our methods, make you worthy to wear the Ozarka button as our accredited representative. Previous experience is not necessary. In fact we prefer to doourown educating. If you have a clean record, are industrious, and have saved up a little cash, here's a real opportunity, if you can qualify for an exclusive territory. We already have 2247 representatives. Territory going fast. FREE, LARGE Illustrated BOOK WRITE Today for illustrated book No. 101 that gives the entire Ozarka Plan. Don't fail to give the name of your county. OZARKA, Inc. 841 Washington Blvd. CHICAGO A Tube Sets A* *ow $39*°