Radio Digest (July 1924-Apr 1925)

February 7 , 1925 RADIO DIGES T— Illustrated How to Construct A. F. Transformers Homemade Amplifier for Your Receiving Set The first step in the construction is the two end plates. These are made up of either hardwood, hard rubber or any of the numerous insulating materials on the 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, 510 North Dearborn St., Chicago market. If hardwood is used these should be cut 2 inches square and Vz inch thick. The center core hole should be drilled 7/16 inch in diameter and the two small holes are made with a number 30 drill. It will be noted that the small holes are located differently in the two end blocks. The one side is for the primary and the other for the secondary wires. The edges of these holes should be well rounded to avoid chafing -of the fine wire. The end pieces are mounted on a bundle of core wires. The space between the end plates is 3 inches. Care should be taken to see that these core wires are kept perfectly straight and parallel. It is suggested that the wires be slightly moistened with oil to avoid rust. After the end pieces are properly spaced the core should be wrapped twice around with two layers of waxed paper. This should exactly fill the space between the end blocks in order to avoid short circuiting the wires on the core. For convenience it would be advisable to let the core wires project from one end plate 1 inch. This will permit mounting in a lathe chuck, thus facilitating the coil winding. The supply spool from which the wire is unwound should rotate with a slight friction in order to avoid any tendency of spinning and thus accumulating an unnecessary length of loose wire. Care should be taken not to attempt winding too rapidly. Start slowly and gradually increase the speed as the work proceeds. The primary winding should be wound in smooth consecutive layers until the diameter is 13/16 inch. In calipering this diameter the sharp ends of the calipers should not scratch or damage the insulation on the wire. Avoid all kinks in the wire. In fact a kink should be treated as a break and the two ends should be twisted together, soldered and then wrapped with a thin piece of silk. The wire must be wound on evenly from end to end. This method of winding avoids any comparatively large differences of potential between layers. Afer the primary winding has been completed it should be tested with a milliammeter or galvanometer and a 6-volt battery. The ends of the primary winding should project FOR A LIMITED TIME ONLY Tod can pui-char* tor «>-S» a IS cell 14 *•!■ RABAT SENIOR battery. Saving St-.IO through direct buying. Tbe Jobber and Dealer* profit now U your*. 14 c«U 4* volt els* *7.oo. Rabat Senior Batteries powerful, noiseless and will ha'rmoai/e, with any Radio Sex Separate cells and patented rubber tork prevent' current leakage and clear glass lubes give vision ol the condition of battcrr Heavy duty s3-16 Kt'xZli with Maceered fibbed grid form the backbone of jrdy battery. Shipped completely charged ready for .nuant wtc And you can save $6.10 by ordering now. RABAT JUNIOR BATTERY S2.1? C. O. d. ( IX CELL* 14 VOLT* HO* M A. CAPACITY) Incomparable tn price and performance 'Designed to satisfactorily operate sets equipped with 3 tubes or lesv Constructed of The ufhe high grade materials as used in our Senior battery Shipped dry, uncharged Order today and save 51 -81. Rabat batteries cao.be recharged at home at a very tow COM Rabat .Super-Charger S3.0O c. o. 4. Is specially designed to satisfactorily recharge any make ol storage "B" battery. Shipped complete ready touse including lamp lockeL, attach ment plug and ^ord You save $1410 by ordering direct SEND NO MONEY Bui write u*,T,oday. advising quantity and type wanted Alter e«*rmn irrg and approving these wonderful baiicnes then pay the Expressman the small COD charges. The Rabat guarantee is back ot all our products. DON'T WAIT ORDER TODAY and save the middle man's, profit THE RADIO RABAT COMPANY ft. Clair Avoorat, C1e*olaa4, Ohio 1767 " " 1 r ifaWnfflrnxr "rmn«f END BLOCKS ON CORE OF WIRES through the two holes nearest to the core holes. It may be advisable to solder a heavier gauge wire to the, ends of the coil in order to avoid a break. When the primary winding is complete two or three layers of parafin paper should be wrapped around the primary winding to provide an insulation between the coils. The secondary coil is wound in the same manner to a diameter of 1 % inches. The beginning and end should be reinforced with a heavier gauge wire and then led out through the end piece in the holes farthest out. "When the secondary winding is complete cover it with a layer or two of parafin paper and then wind tightly with tape. The complete coil is mounted on a wooden or fiber base plate and fastened in place by means of four angles as shown. The ends of the primary and secondary are secured to binding posts and marked in the usual manner. — J. Foubert, Cornwall, Ont. For the Real Shut-in All Radio tables to be used near or over the bed are constantly jarred along with the sick persons nerves by stumbling feet and careless bumps. The following is a plan for a Radio set table that may be instantly removed without lifting or disturbance of any kind. The top is of wood, long and wide enough to hold the set and any switches needed. The metal parts are all easily obtained from a plumber's supply store. 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 OIA— 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 'A Volts, .25 Ampere Platinum Filament Amplifier and Detector Shipped Parcel STA^,ABD $050 Post C. O. D. TYPES £4 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. 21 Norwood St. Newark, N. J. For the table illustrated a piece of threeply bass wood was used. Material List 1 Top 28 inches long, 15 inches wide and % inch thick. i t %-inch iron pipe 42 inches long. 1 %-inch flat headed bolt 8 inches long. 1 piece of pipe that is large enough to just fit over the pipe used for the arm, 8 inches long. 2 iron straps of the proper size for the arm. The arm may be made of one piece of pipe bent into shape or it may be made of short length^ put together with elbows. The holder which carries the arm is fastened to a wooden bed inside the side board with iron straps. If to be used nonclevful f w davtli THt COM. without tosses IJNCLE SAM MASTER Cflll TUNING VAJEMj I — Wound on moulded hard rubber. 2 — Increases volume 50% to 250%, also selectivity, over old type. 3 — Eliminates all adhesives. 4 — One hole mount and thin gold-plated compensating spring contacts. 5 — The only coil of its kind wound with Ambassador Litz wire. FREE! Ask your dealer or send us four cents in stamps for wiring diagrams of oirouits in which this remarkable coil can be used. UNCLE SAM ELECTRIC CO. 217 E. Sixth St. Plainfield, N. J. BLUEBIRD Radio Tubes Distinctly New AND EFFICIENT, satisfying every radio fan's wish in performance and price. Our direct sales plan enables us to sell at this low figure. "Bluebird" assures increased range and undistorted volume. Type 400 — 5 Volts, I Ampere Detector Tube Type 40 1 A — 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— I '/z 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 Wood and Foil Make Cartridge Grid Leak The grid leak shown is nothing but a stick of wood marked with a pencil, with tinfoil caps placed on the ends and bound with a piece of twine. In order to make this leak of a permanent value it is only necessary to paint the whole thing except WOOD PENCIL MfcRK s •TINFOIL. the very tips with a waterproof substance. This is the first homemade leak I have seen that can be mounted in the regular grid leak forms or supports. — J. Forman Smith, Sylacauga, Ala. on an iron bed, fasten with bolted collar straps. When properly constructed the top will turn and also the arm at the side of the bed. The set can be instantly swung out of the way. The top should be stained and waxed and the iron parts enameled black. In making the table adjust the measurements to individual needs and requirements.—Morey Studios, Ottumwa, Iowa. * Who is buying LIBERTY this month? Friends ot people who bought the LIBERTY *&'.' Last Month Manufactured by LIBERTY TRANSFORMER CO.X 555 N. Parkside Ave. Chicago "Lo Loss' Tube Socket Checks Current Losses What is it that saps current strength? Insulation leakage, poor contact and mutual capacity between parts. The Premier LO LOSS Tube Socket is specially designed to stop such losses. The bakelite cross section is thin to prevent phase angle losses between terminals. All metallic parts are arranged for minimum capacity. Positive contact is insured by cam action lock and self cleaning action of contact spring on tube prong. One piece contact springs have twice ordinary deflection range. Skeleton barrel permits inspection of contacts at all times. Price 90 cents Send for Bulletin No. 94 showing complete line of Premier Quality Radio parts. Ask your dealer for Premier free hook-ups. If he cannot supply them, write us, mentioning his name. Premier Electric Company 3810 Ravenswood Avenue Chicago mmim Quality Radio Parts