Radio mirror (Jan-Oct 1923)

October 6, IS RADIO DIGES 7— Illustrated Building Up Fixed Condenser Values Five Different Series and Shunt Combination For the experimenter who wishes to use the larger size variable condenser in the circuits now popular requiring small condensers, the following stunt will prove valuable. The capacity curve of the large WORKSHOP KINKS? EARN A DOLLAR— THERE are many little kinks worked out at home that would aid your fellow Radio worker if only he knew about them. There are new hook-ups, new ways of making parts and various unique ways of operating sets that are discovered every day. Radio Digest is very much interested in obtaining such material. Send them in with full details, including stamped envelope, so rejected copy may be returned. The work must be entirely original, not copied. RADIO KINKS DEPARTMENT, Radio Digest, 123 W. Madison St., Chicago SWITCH CONTROLS THE CAPACITY v&l I 43P/.ATE VARIABLE .OOltlFP or , "2 3 J ooosnpo. » A,B, <3/vE 5 A3 B, 6lV£S AjB2 6ive% fr$%3 CVUC5 -#HI — If .OOI OOI .0O05 -&-\\ POI .OOI -# OOI .0DO5 OOI ^£2L-ZTooos = 00025 Mfp = .0005 nf-o =s .OOI UFO. = .0015 tiro .002$ riFo Connecting Testing Sets That Use Vacuum Tubes When the construction of a receiving set empolyiriK vacuum tubes either as detectors or amplifiers is complete, the filament or A battery should first be connected up to be certain that all thi nections to the tubes and control rh< are correct for filament lighting. The plate or B battery should always be com last so as to eliminate the possibility of having the tubes burnt out through improper connection of the B battery to the filament terminals. — Peter J. M. Clute. Schenectady. N. Y. A single circuit set will pick up almost as many stations as a more complicated one, but it may. happen that it does not pick up one station at a time. in the transformer. If the case, binding posts, vibrator and the various equipment are still in place, save them. Many things not needed at first will become of value later. Separate the coils to make two independent coils. Take the primary winding — the larger wire around the core — out of variable may be reduced all along the scale by using a small fixed condenser in series with it. Thus a .001 mfd. variable may be made into a .0005 by using in series with a .001 fixed condenser; or it may be changed to .0002 by using a .00025 fixed condenser. This method of reducing the capacity of a variable somewhat distorts the capacity curve; i. e. reduces the upper part of the scale in greater proportion than the lower part, but this is especially desirable with condensers of the type of the Connecticut variable. In the diagram two fixed condensers of .001 mfd. and .0005 mfd. are used with a 43-plate variable so that five different series and shunt combinations are possible, varying from a maximum capacity of .00025 mfd. when all are in series, to a maximum of .0025 mfd. when all are in shunt. Switch A is used to obtain the series combinations, switch B being left in the first position (to the left). "With A in the third position, the variable only is in the circuit. The fixed condensers are shunted across it to increase its capacity by moving switch B to the second and third positions, switch B being left in the third position (to the right). It will be noted that switch B has two blades. The condensers used should be mica insulated and of guaranteed capacity. — Russell Skeeters, Des Moines, la. Audio Frequency Transformer Pick up from your neighboring garage ■a. few Ford coils. These coils are divided SECONDARY PRINAR.V into two small coils each about 1% inches long which constitute the secondary. These two coils and the cores are used both and keep the core — the bunch of annealed wire — in the center. If you want to know how many layers are on a coil count them. It's good practice. On most coils there are 35 and 37 layers. If we have a 35-layer coil and desire a 10 to 1 ratio it is necessary to have a 30 to 3 coil. First, five layers of the coil are pulled out of the inside and the ends are brought out free. Remove 30 layers from the outside of the remaining coil and bring the ends out free. It will now be easy to place the smaller coil into the larger one. "Wind enough tape around the smaller coil to make it fit snugly into the larger coil. Bring the ends from the large coil out at one end and the ends from the small ^^d^C On Approval For 30 <t Zobel-Stein laboratories 322 9TST.BRQ0KUN.N.Y.S0UIH26S0 -Improved Ground Clamp Equipped with Fahnestock Patent Wire Connectors Easily Attached No Soldering. For Radio Use Only At Your Dealers Fahnestock Electric Co. Long Island City, N. Y. METALECTR1C SOLDERING IRON (The All-Metal Instrument) A Solution to the Small Soldering Problem of the Discriminating Assembler. Unbreakable Construction — Economical Operation on any Electrical Circuit — Interchangeable Tip. $5.50 From your dealer or write Post Electric Co., Mfrs. Dept. 509, 30 East 42nd St. New York City coil out at the other end and keep in mind which is which. The larger coil is the secondary and the smaller the primary. Wind the core with enough tape to fit well into the inside of the small coil. If you want a closed core transformer, the usual kind, bend back the ends of the core as shown in the illustration; it will serve the purpose admirably. If you want an open core type leave the core as it is shown. — Edwin Foist, Phoebus, Va. Keep Rust Out of Receivers The diaphragms of certain types of telephone receivers sometimes become rusted after long use and even the pole pieces themselves become slightly covered with rust which will interfere with the vibration of the diaphragm. When this is noticed, remove the cap and wipe the magnets and diaphragm with a soft cloth dampened with sewing machine oil. Care should be used not to bend the circular disc. Testing Crystals The more ambitious of experimenters wlil find it an interesting and instructive pastime to test out crystals of different kinds of sensitiveness. While thousands of crystals and combinations of crystals have been tried out, a new combination may accidentally be discovered that will bring results well worth the trouble. iiiiiiiimiiitmiiiiiiiiiiiiHiiiiimiiHiiiiiiiinii MISSING WHAT YOU GET V"OUR set is probably bringing in DX stations you never hear because your rheostat cannot control your filament action. The Fil-Ko-Stat gives infinite adjustment and enables you to magnify the weak stations and bring them in strong and clear. full resistance M g Ohms, adjusted to J ALL TUBES. "Avoid the use of inferior powdered carbon rheostats." 2 At All Dealer: in High Grade RADIO SUPPLIES rRO-STAT Matie and Guaranteed by Dx Instrument Co.. Hanisburg, Pa, Sole International Distributors. Radio Stores Corp., 218 W. 34. N. Y. City Do you wonder how we can do it ? A great many radio men have wondered bow for example we can offer a genuine Automatic Electric $10 head set for $3.65. The reason's simple enough. When we buy we don't merely place an order for a dozen or so. We buy big! We buy out a complete stock or the entire output of a factory. We bought 40,000 of these Automatic Electric head sets. We got a special price by paying spot cash for the lot — and that's how we can offer these $10 head sets for The Automatic Electric head set embodies style and design proved by use and experiment to be the best. Coil wound with about 6500 turns of No. 40 enamel coated copper wire. Di' rect current resistance approximately 1600 ohms. Impedance and average music and voice frequency (800 cycles) is 21,000 ohms. 3^ *$965 WATCH FOR OUR BIG SALE ON WESTERN ELECTRIC V.T.-2's We Just Bought 10,000 of Them from the Navy HONEYCOMB COILS 1,500 Turns $1-50 1,250 Turns 1.50 1,000 Turns 1.25 750 Turns 1-00 250 Turns 7S 150 Turns 60 100 Turns 50 75 Turns 40 50 Turns 40 35 and 25 Turns .40 CAPT. SCHOONHOVEN REINARTZ COILS $1.95 COCKADAY COILS $1.95 U. S. A. SIGNAL CORPS, AVIATION TYPE 194-W WESTERN ELECTRIC PHONES Each Phone Cap is covered with large, soft rubber ear cushions, and an aviation leather helmet goes with each set ! These are the only phones to pass the Government specifications for sensitiveness and loudness, the requirements called for in aircraft reception. Special at $7.95 SINGLE CORDS SUPERSENSITIVE MICROPHONE TRANSMITTER $2.45 VARIABLE CONDENSERS $7.00 val., 43-pL Vernier. . .$3.95 $6.50 val., 23-pl. Vernier... 3.45 $6.00 val., 11-pl. Vernier... 2.95 $1.75 val., 3-pl., Vernier 1.15 $4.30 val., 43-pl. NOW 1.75 $3.70 val., 23-pl. NOW 1.45 S3 JO val., 11-pl. NOW US $2.2S val., 5-pl. NOW 1.25 FRESHMAN VARIABLE GRID LEAK AND CONDENSER W-00 figValue DOC ELECTRIC SOLDERING IRON ONE YEAR GUARANTEE $2.45 THE LARGEST RADIO STORE IN AMERICA" /I? MAIL ORDERS, ALL MDSE. GUARANTEED BY US TO BE OF FIRST QUALITY 509 South State St., Dept. D 10-6. CHICAGO, ILL. ALL -SMXV5E Iffc LARGE OR SMALL, SHIPPED TO YOU \ PROMPTLY IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIMIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIHIIIIIIIIII IHIIIIIIIIIIII