Radio age (Jan-Dec 1924)

RADIO AGE for May, 1924 The Magazine of the Hour 21 How to Build a Basket Wound Variocoupler and Variometer THESE instruments are practically of the self-supporting style, doing away with supporting frames and losses due to masses of dielectric and reducing distributed capacity by basket winding. They are very light and compact, being especially suitable for small portable sets. Materials needed: About ten feet of No. 3 reed, such as is used for weaving baskets in schools. (If reed cannot be secured, common parlor matches will do, for the variocoupler, but because of the necessary curving of the rotor of the variometer reed must be used for this rotor); a rubber band; about a foot of strip brass %e inches wide by about No. 14 B. & S. gauge; a %g inch piece of brass tube for a shaft; necessary No. 26 D. S. C. wire for variocoupler and No. 24 D. S. C. wire for variometer; cylinders to wind the coils on. For the coupler one cylinder of 2^4 inches in diameter and one of 3 J/2 inches in diameter will be needed. These can easily be made by cutting two discs from heavy cardboard or cigar box board and wrapping very heavy wrapping paper around these discs to make a cylinder. Cut the reed in 2-inch lengths. For the rotor you will need 20, for the stator 23. Mark well these numbers or the winding will not come out right. Snap a rubber hand around the larger of the cylinders, then insert one end of the reed under the rubb ■ band, spacing the reeds evenly around the cylinder — -see Figure 1. This will hold reeds in place around the cylinder until the winding starts. Now take your No. 26 wire and start winding. Raise the ends of two reeds slightly, slip the wire under these two, then turn the wire over one reed and then under two again. Continue this way until you get the number of turns desired — see Figure 1. I find that 90 turns on the primary and 54 on the secondary the best for a three-tuned circuit. For single circuits you will need fewer turns. When you have wound half the number of turns desired, skip a place %o inches wide so support for the shaft can be fastened on the reed. When coil is wound slip off of cylinder and then by catching the windings between the first finger and the thumb (the finger, of course, being between two reeds), squeeze the wires tightly together and tie with a thread. Tie at four or five different places. Cut off all reeds excepting four close to the wire; these four are to hold the leads of the primary and secondary. Dip the coil in melted paraffin and it will become very rigid. Clamp the supports on the reed. The supports are flat strip brass 5Ac, inch wide, bent as illustrated and clamped on the reeds between the two halves of the winding. The shaft is fastened to the rotor by a drop of solder between the brass support By W. E. KESSLER A»3 «FRo and the brass shaft. Note that because of the spacing of the reeds, the hole for the shaft may not come at a point half way between the ends of the brass strip used for supports — see Figures 2, 3, 4. Repeat the above procedure, using the smaller cylinder, then insert the shaft, fasten rotor to shaft and the instrument is completed except for the pig tail wire which comes out through the hollow shaft Two holes should be drilled through the shaft at each end just inside of the brass supports for the stator. Pins inserted in these holes after the instrument is assembled centers the rotor. By providing pins in the brass support for stator the pin in the shaft will engage the pin in support and so form a stop so rotor cannot be turned all the way around. If the shaft is made in two pieces, the ends fastened together inside the rotor by some insulating material, wood will do, all body capacity will be done away with. By winding the coil without a space in the middle for supports and then placing supports at edge of coil, a 180-degree coupler can be made. To build a variometer: Use No. 24 wire for this instrument. Make the stator the same as variocoupler, except that 80 turns are used in place of 90. For the rotor: Wet the reed and wrap around a rod about 1 inch in diameter. Let reed dry on this rod. When taken off it should spring out to a coil about 3 inches in diameter. If it does not, work it over a cylinder about Zl/i inches in diameter while dry. Let it remain there for a while and it should then be about the size desired. Cut this coil into 20 curved lengths 2 inches long. Be very careful and cut all the same length. Now cut a disc from a cigar box board 2>yAa inches in diameter and cut a hole in the center 2% inches in diameter. Use some small brads and tack the 20 curved pieces of reed to the edge of this disc. See Figure 5. Do not hammer brads clear in up to the head, as they must be removed later. A 2}^-inch cylinder should be placed through the hole in the disc. If it has been made right the ends of the reeds should just touch this cylinder. Start %e inches from the center and wind toward the ends of the reeds that touch the cylinder. Use same kind of winding as for the variocoupler; that is, two under and one over. When both sides have been wound with 40 turns each, 80 turns for the rotor, solder the ends together in the center, dip in hot paraffin, then remove from the cylinder. Pull out the brads and then break the disc so it can be removed. Make the supports the same as for the variocoupler. Jefferson Electric Co. On the first of April, Mr. Paul Green, formerly Advertising Manager for the Cole Manufacturing Company took over the duties of Advertising Manager and Director of Sales Promotion for the Jefferson Electric Manufacturing Company, 426-430 South Green Street, Chicago, Illinois, manufacturers of transformers including a full line of radio transformers and ignition coils. Mr. Green undertakes this work with a background of more than fifteen years of experience in advertising and merchandising, a very, large part of which covered electrical and mechanical lines. POTOR F/G-lSRE Z STRIP ClAMffS 4/iouM ueso