Radio Digest (Oct 1923-July 1924)

February 9, 192 J, RADIO DIGEST — Illustrated How to Make a Lighthouse Keeper's Receiving Set Part I — Portable Set Suitable for Everyday Use By S. JR. Winters A PORTABLE Radio receiver, representing a cash investment of only $20, and so simple in structural details that a person with the slightest elemental knowledge of electricity can assemble the parts, has been designed by A. W. Tupper, assistant engineer of the Lighthouse Service, United States Department of Commerce. Furthermore, the set is compact, the cabinet, instruments, and dry-cell batteries weighing barely 15 pounds. A single vacuum tube is used, which, besides the headphones, is the only expensive unit used. This receiving equipment was designed especially for keepers of lighthouses — those lonely guardians of property along our 44,000 miles of coast line. One of these lighthouses, for instance, is perched on a rock in the Pacific Ocean, miles from land. The installation of the receiving set about to be described on this rock, will dispel the isolation by bringing civilization— music, church services, financial reports, lectures, etc., — into mid-ocean by the magic of the invisible electromagnetic waves. Adapted for Universal Use This compact Radio receiving set, perfected fortunately, is not limited in usefulness to the lighthouse. It is equally adapted to home, office or field, where inexpensiveness, simplicity, compactness, and long-distance reception are sought. The opportunity for the farmer to display his mechanical skill in making and assembling the parts entering into the construction of the Radio telephone equipment is not to be discounted. The city dweller, too, who is swinging away from electric circuits involving cumbersome units and bulky storage batteries, will appreciate the possibility of building and assembling a set of such light weight that one person could easily carry cabinet, instruments, and batteries anywhere he might go. The materials necessary for building this simple form of regenerative circuit have been so explicitly outlined by the Lighthouse Service that even the size and number of screws are specified. Fortunately, some of the materials are likely to be found around any home which houses a person with a mechanical turn. Moreover, the various parts indicated are not suggested for use on mere theory, but these sundry units have been tested for several months and their suitability established beyond a doubt. The simplicity of the assembly of the instruments is not likely to be marred except in one possible instance, namely, the "making of the proper connections of the two spider web variometers or coils. This obstacle may be avoided, however, by faithful adherence to the diagram or hook-up illustrating one part of this series of articles. Materials Necessary The materials required are the following: One Hi -volt vacuum tube for detecting the Radiophone signals, type WD11 being used by the Lighthouse Service; one vacuum tube receptacle; one pair of headphones; one 22%-volt B battery; one dry-cell battery; one 23 or 43-plate variable condenser with vernier; one telephone condenser of .00025 mfd. capacity; one grid condenser of .0005 mfd. capacity; one grid leak; one piece of fiber or hard bristol board about ^ inch thick and 8 inches square; Yi pound of number 24 gauge enameled magnet wire; 7 feet of tinned copper hook-uji wire or heavy bell wire; one rheostat for controlling the filament of the vacuum tube; one piece "A-lnch diameter dowel stock, 5 inches long; one piece %-inch diameter dowel stock, 8 V4 inches long; three or four pieces of tinfoil for covering back of panel; four binding posts; four machine screws No. 6, about Vi inch long, with nuts; one piece of brass, about A incn thick, % inch wide, and 6 inches long, for making end supports for coil shafts; three dozen copper or brass wire terminals; one dozen number 4 round-head brass wood screws, % inch long. Materials for Cabinet This ho: o receiving set in volves the building of the cabinet as well as assembling of the infll tained therein. Therefore, the materials for making the container are quite specific. Obtain a piece of dry close-grained wood, about % inch thick, 13 inches long, and 10% inches wide, for the front or panel. Bakelite or other insulating material may be used if preferred. The remainder of the cabinet may be of any kind of wood, although the model receiving sets built by the Lighthouse Service is of white pine-, % inch th The dimensions of the other pieces for the construction of the cabinet are as follows: Bottom and top, 14 inches by 8% inches; two ends, 8% by 10% inches; back, 13 V4 by 6 inches; hinged back or door to the compartment containing the batteries, 1 3 1-. by 4% inches; shelf, 7% by 12% inches. The other essentials for securing the cabinet in position include four pairs of small brass hinges and screws and some 1% -inch wire brads; six brass screws, number 6, about % inch long, for securing the back in place; and soldering material. Making the Cabinet The construction of the box or cabinet involves the making of a groove, V* inch wide and % inch deep, in each sidepiece near the front into which the front board or panel is slipped. Any kind of wood, about % or % inch thick, will do. The panel should, preferably, be a piece of close-grained wood M inch thick. (Continued on page 10) Complete Your Radio Outfit Bring Out the Best in Your Receiving Set with a Bristol TftADE MARK AUDIOPHONE AKO. O. 8. PAT. OFFICI LOUDSPEAKER IT TOOK six years to develop and perfect the that your own family and friends can enjoy it Audiophone. That is more time than the with you. average person cares to spend on a Loud Speaker The finish is a beautiful, dull gold bronze, for his receiving set. But here it is, all ready for you to use by simply Made in 77,ree Sizes connecting to the set. Senior AiicHc>phone Price $32.50 & Junior Audiophone rnce 22.50 No auxiliary batteries are necessary. Baby Audiophone Price 12.50 The tone is big, full, and rich, and without that When signals are not sufficiently loud to give good results i . r. i i • • • with the loud speaker, Bristol One-Stage rower Amplifier scratchy, tinny noise so often heard in receiving. is recornmendecl to buiId up the power so that it can be heard It can easily be heard all through the house, so even in a large hall. ....... Price $25.00 Ask (or Bulletins Nos. 3006 and AY-3011 THE BRISTOL COMPANY, Waterbury, Conn.