Radio age (May 1922-Dec 1923)

RADIO AGE— "THE MAGAZINE OF THE HOUR' 11 How to Construct a Good Reinartz Set (Republished in response to scores of requests) By F. D. PEARNE Chief instructor in Electricity at Lane Technical High School FOR the amateur who wants to build a real receiving set and does not feel that he can afford to spend the mdney, I submit the following specifications of the Reinartz tuner, which, according to my many correspondents, is giving far greater satisfaction than the wellknown vario-coupler artd variometer set. This set is claimed by many users, to bring in signals which cannot be heard with the other well-known types, and the small investment required to build it is one of the features which recommend it to the experimenter. All of the inductances are wound upon the same form, which are of the well-known "spider web" type. Construction. The mounting is made by cutting out a disc of fibre one-sixteenth of an inch thick and six and one-half inches in diameter. If fibre cannot be obtained, good heavy cardboard can be used, but it must be very carefully varnished with shellac before the winding is put on. Cut out the disc as described and divide the outside edge into eleven parts. Draw a circle two and one-half inches in diameter upon the disc to locate the bottom of the slots, then at each of the divisions cut a slot one-eighth of an inch wide from the outside edge to the inner circle so marked. After all the slots have been cut, a coat of shellac varnish, or celluloid cement, is put on and, when dry, the form is ready for winding. It is a good idea to study the circuit as shown in Figure 3 before starting to wind. Note where the taps are taken off, as a great deal depends upon just the right number of turns being used. Leave all taps at least twelve inches long, so that no splicing will have to be done when the inductance is connected to the switches. The best wire to use for the winding is No. 26 cottenamel or silk enamel insulation, although plain cotton insulation will do if the maker is careful in his work. Begin winding at the bottom of any one of the slots, leaving an end at least twelve inches in length for connections. Wind in and out of the slots as shown in Figure 2 until fifteen turns have been put on. In count 2^ I FIGUR£ / ing these turns after they have been put on remember that only one-half of the turns will be visible on one side of the disc, so that when seven turns show on one side and eight on the other, it means fifteen complete turns. When fifteen turns are in place, make a twelve-inch loop, twisting it together, so that this twist will come up tight to the slot, then the tap will not lose its identification among the numerous other taps to come. Continue the winding in this way, taking off a tap at every fifteen turns until sixty turns are in place. At the last turn cut the wire off, leaving the twelve inches for connection. If these instructions have been followed faithfully there will now be three taps and two ends projecting from the disc. It is a good plan to bring out these taps in diflerent slots; that is, the first tap comes out in the next slot to the one in which the coil was started and the next tap in the next slot, etc., as this makes the identification of the wires much easier. This FIGURE 2 . coil is shown at the bottom of the diagram in Figure 3, and is marked "inside coil." Now start the next coil in the next vacant slot, leaving the customary twelve-inch end; wind one turn only and bring out a loop. Continue in this way, taking a tap off at every turn until you have ten turns. Instead of cutting the wire at the end of the tenth turn, bring out another tap and wind fifteen more turns before you bring out the next tap. After the tap on this fifteenth turn, wind twentyeight more turns, tapping them at every seventh turn, except the last one which will be a single end, as it is the finish of the winding. Now check up the number of turns with the diagram Figure 3 and see that the correct number of turns have been put on. There should be sixty turns on the inside coil and fifty-three on the outside coil. Now after the winding is completed, paint the coil all over with some insulating varnish, such as shellac or celluloid cement. Both of these windings together will just about fill the form. The best way to mount the coil is to cut off a piece of curtain-pole (wood) about one inch long, place it against the center part of the disc and fasten it to the panel with two brass screws. (Do not use iron screws, as they will tend to dampen the oscillations.) If the set is to be mounted in a cabinet, it will be better to mount the coil with a piece of curtainrod on a separate piece of wood, in an upright position, as this will give better access to the wires when it comes time to make the connections. The switches and contact points can be purchased at any radio supply store. Two variable condensers are necessary, one shown at "C" in Figure 3 should have a capacity of .001 M. F. and the one shown at "D" in the same figure should have a capacity of .0005 M. F. The rest of the apparatus required is the same as that used in any other regenerative set, viz.: One grid leak and condenser, one detector tube and socket, one storage "A" battery (6 volts), one plate, or "B" battery (twenty-two and one-half volts), and one pair