Radio Broadcast (May-Oct 1926)

RADIO BROADCAST ADVERTISER 265 diameter in the neighborhood of 3-16 inch; a little brass or copper tubing which will fit rather snugly over the glass tube; some thin sheet brass, copper, or even a tin can if the latter is bright and clean enough to take solder readily; and some sealing wax. First, soak a piece of the muslin in the ink and dry thoroughly over a radiator or stove. Next cut your tubing into lengths to suit (an inch and a half is about right) by nicking with a file and breaking with the fingers. Now make two ferrules out of the copper rf Brass f'i'i Ferrule"^ Inked , Brass . Muslin \ Ferrule ® ® •Glass Tube Solder here and trim flush' © FIG. 4 or brass tubing about j-inch long. If you can't get the right size tubing, roll a piece of j-inch wide brass or copper foil around each end of each piece of tubing, and solder the joint. One more thing and you are ready for the assembly. For each resistor you will want two "T" shaped pieces of the thin metal. See A, Fig. 4. Cut the muslin into strips a half-inch less in width than the length of the glass tubing. Roll one of these strips up tightly until the roll is about an eighth of an inch in diameter and clamp both ends in the "T" shaped metal pieces by curling the top ends of the "T" pieces around the ends of the roll. Assemble as shown in C, soldering the ends of the "T" pieces to the edges of the end ferrules, and seal both ends by dipping in melted sealing wax, leaving long enough for the wax to flow all around between the glass tube and the ferrules. The excess wax on the outside can be easily removed with a knife. If difficulty is met with in completely closing the ends of the assembled units with the hot wax, the whole device may be filled with melted wax. If permanency of calibration is desired, it will be necessary to make airtight seals at the ends; otherwise the resis-. tance will vary with atmospheric changes. The writer made up a dozen of these units, using Higgins ink, and varying the length between the "T" clamps from \ inch to one inch, measuring the resistance after assembly with a B battery and highresistance voltmeter. The twelve ranged from 50,000 to about 250,000 ohms, and have been used with excellent results in resistance-coupled amplifiers, etc. W. B. Harrison, Miller School, Virginia. An Easy Method of Doping Solenoids THE following method provides all the advantages of a "doped" coil and, as will be obvious, practically none of its disadvantages. Having procured from a Kodak dealer a sheet, or sheets, of celluloid (this is as thin as tissue), and from a druggist a pint bottle of amyl acetate, first cut a strip of celluloid to cover a coil form of the desired diameter and length. If the strip is not long enough to overlap half an inch, join two pieces by softening a narrow band on the ends of two strips with amyl acetate and pressing them together. Bind the strip around the coil form, first applying amyl acetate in two or three places to the under side of the strip and the overlapping edges, and wind fifteen or twenty turns of cotton thread around the celluloid. Leave it for five or ten minutes until the celluloid is set. Then remove the thread and wind the coil as usual, fastening the ends as you usually do. Now apply amyl acetate to the coil with a brush, fairly liberally, so that it will soak through to the celluloid. Allow it to dry slowly for half an hour, and then place over a register or radiator so as to volatilize all the chemical. The acetate will have dissolved the surface of the celluloid to the consistency of cement and, as it dries, the coil wili be firmly held. At the same time, the chemical will have evaporated practically entirely from the coil and it may be slipped from the form. To wind a primary over a secondary, put a narrow strip of the celluloid over the secondary and repeat the process. E. S. Anderson, Springfield, Massachusetts. Two Practical Methods of Mounting Crystals FOR facility to change crystals rapidly and to obtain dependable contact in the circuit, this method of mounting crystals in miniature lamp bases will be found hard to equal, considering the cost. Either the candelabra type of miniature lamp, or the bayonet type of lamp base, and corresponding sockets, are used as the means of holding the crystals. See Fig. 5. To prepare the lamp bases, the glass and plaster of Paris is broken out, and the crystal is hot-leaded into the base. Contact is made with the lamp socket through the Crystal in Lamp Base-^ Bayonet Type Socket Candelabra Type Socket FIG. 5 terminals as is the case with the electric bulb, but only one side of the circuit is used. By mounting several grades and types of crystals in these bases, change can be made immediately without loosening screws, and with a minimum of delay. G. A. Luers, Washington, District of Columbia. Improvising Your Own Bus Bar SOFT drawn copper wire can be made into very effective lengths of bus bar with which to wire receivers. Usually this soft drawn copper wire is sold in rolls of 100 feet and any gauge may be obtained, depending upon the choice of the radio constructor. To change the soft copper wire into stiff lengths, merely cut the roll into 10 foot pieces. Fasten one end of a piece in a vise and the other end into the jaws of a hand drill; then by alternately turning one way and then the other and at the same time exerting a pull on the wire, it will be observed that the wire stiffens perceptibly, after which it may be removed from the vise and cut into the desired lengths. Do not make the wire-too stiff by the alternate turning or else it will become brittle, and break when bent. Gene Ralele, Montreal, Canada. ■jf Tested and approved by Radio Broadcast -^r ^mericanjransformer(ompan YITHERE the power supply for VV receiver operation comes from a steady source, such as the house lighting circuit, radio reception is greatly improved, providing properly constructed B and A Eliminators are employed. This is due to the steadiness and constancy of the alternating current supply as contrasted with the internal changes which are always going on any type of battery, storage or dry cell type. The American Transformer Company offers two units — the AmerTran Power Transformer and the AmerChoke — especially adapted to the use of the 1\ volt power tubes in the last audio stage. Their efficiency may be absolutely depended on in the type of audio amplifier required. The Power Transformer also has filament supply windings for the power tube in the last stage and for the rectifying tube. It supplies sufficient plate current, after rectification, for the operation of the set. The AmerChoke is designed primarily for use in filter circuits. As an output impedance for by-passing direct current from the loudspeaker it is equally efficient and more economical than an output transformer. The AmerTran De Luxe Audio Transformer gives faithful amplification with natural quality over the entire audible range. For the best in audio amplification use this transformer in both stages. AmerTran De Luxe, 1st Stage . $10.00 AmerTran De Luxe, 2nd Stage . 10.00 AmerTran AF-7 (3^-1) 5.00 AmerTran AF-6 (5-1) 5.00 AmerTran Power Trans. PF-45 15.00 AmerTran Power Trans. PF-52 18.00 AmerChoke Type 854 6.00 Write to-day for free booklet "Improving the Audio Amplifier" and other data designed to make radio reception simpler and more realistic American Transformer Co. 178 Emmet Street Newark, N. J. AmerTran Products Are Sold Only at Authorized AmerTran Dealers Transformer Builders for "■ • ' ■ Over Twenty-Five Years