Radio Digest (Oct 1923-July 1924)

October 13, 1923 RADIO DIGEST — Illustrated 17 First Steps for Beginners in Radio Chapter XX — Useful Information and Formulas IN THE last chapter of the series will be mentioned a few of the tricks of the trade that cannot be classified under any other heading. There are a number of little kinks, not *oo well known, that mm assist the Radio beginner. Often a set will be noisy, for no particular reason beyond, perhaps, noisy tubes. To overcome this it is necessary to use a form of electrical filter to get rid of the unwanted sounds. For the purpose use is made of three .01 megohm grid leaks connected in series in the plate circuit of the first amplifying tube, as shown in Figure 65. The connecting of the two .002 mfd. fixed condensers is also shown. The resistance acts to stabilize the circuit, and the condensers by-pass the undesired noises, reducing them greatly. This will cut the signal strength to a certain extent, but the music will be much clearer. A similar arrangement may be used when audio frequency amplification is added to the Armstrong flivver circuits, but larger condensers may be found necessary. By experimenting with leaks and condensers of different sizes, it is possible to filter out the greater part of the whistle always present in the Armstrong super-circuits. Figure 66 — Condenser for modulating loud talker The filter is connected in the plate circuit of the first audio tube, and the secondary audio amplifier will be but little affected by the whistle. Improving Quality of Iiond Speaker The quality of music from a loud speaker can often be improved by the addition of the condenser and switching device shown in Figure 66. A .002 fixed condenser and three-point switch are connected into the last audio frequency amplifier tube circuit as shown. By adjusting the switch, much of the harshness of the music is removed, and the tones are reproduced much more clearly and sweetly. The effect is not so pronounced when headsets alone are used on a Radio set, but on a loud talker the effect is very noticeable. The changes in wave lengths made necessary the loading of many receiving sets to enable them to reach the greater lengths. To overcome this condition there are two methods, either to shunt the inductances with a fixed condenser or to add inductance in series in the different circuits. With a single circuit tuner it is very simple. A coil of 50 turns of wire on a 3-inch tube, tapped every 10 turns, connected in series with the aerial lead, is all that is necessary. The alternative method is to connect a .0005 and a .001 fixed condenser with a three pole switch as shown in Figure 67, so that either condenser may be shunted across the inductance, as desirable. In sets using a variable condenser in the aerial circuit the better By Thomas W. Benson, A. M. I. R. E. method is to install a pole changing switch, so the condenser can be connected in series or parallel with the aerial inductance, for better tuning. Loading Circuits With double circuit tuners both circuits must be loaded. Either of the above methods may be employed in the primary Winding and Tapping Inductances A few suggestions as to the winding and tapping of single layer inductances are not out of place. As an aid in designing the windings, the following table, which gives the number of turns per linear inch, will be valuable. With this table one can readily deter 1/10 necoHtv GRIDLBAKS length for each tap at the beginning of the winding and smaller Jumps at the end. This is due to fact that the length does not vary directly as the number of turns but is <-<|u;il to a con multiplied by the square root of the : uct of the inductance and capacity, order that the wave length of a circuit may increase regularly with the number of taps, the tapping of the coll should be done in the following manner: First we must determine some desirable percentage of increase. Then, from the following table Belect the proper constant for that particular increase. Figure 65 — Filter for cutting out tube noises circuit. In the secondary circuit, however, the condenser across the secondary should not exceed .0005 mfd.; and where a condenser is used for tuning, it will be necessary to add an inductance similar to that used in the primary circuit. In a three circuit or tuned plate regenerative receiver, where a variometer is used to tune the secondary circuit, a small fixed condenser, say .0005, may be connected across the rotor to load the circuit, and if regeneration is difficult to obtain, another fixed condenser across the plate variometer. When a tickler feedback is employed, the plate circuit requires no loading. When the dry cell tubes are used in a tuned plate circuit, it is often difficult to obtain regeneration owing to the low capacity between the elements in the tubes. One method of overcoming this is to connect a .0005 mfd. condenser between the grid and plate. The condenser serves to transfer part of the plate circuit energy back into the grid and thus obtain regeneration. Another method of gaining the same result is to take some flexible wire (lamp cord will do nicely) and wind three or four turns in inductive relation with the stator of the grid variometer, and the same number close to the plate variometer,connecting the ends of the two windings. This forms what is termed a link circuit and will transfer part of the plate energy back into the grid. If results are not obtained immediately, it may be necessary to reverse the connections to one of the coils. 15c Lettered binding posts, complete, sel eight, 60c; two sets, $1.00. Prepaid, same day. .Stamps accepted. Everything in Radio. Ask for quotations. List for stamp. Kladag Radio Laboratories, Kent, Ohio. YouDon'tNeed TllhfiCto Ket out ot town. If you * ••"^^want new stations on your crystal set WRITE ME TODAY. Mine works 400 to 1,000 miles without tubes or batteries I Thousands have bought my plan3 and now get results like mine. CHANGES OFTEN COST LESS THAN A DOLLAR. Send self-addressed envelope for further information. Leon Lambert, SOI South Volutsia. Wichita. Kansas. Do you Know why the Mu-Rad sells, Mr. Dealer? m Simply because to hear the Mu-Rad is to buy it! One of Chicago's largest radio stores sells the Mu-Rad entirely by demonstration. Their records show that 8 out of 10 demonstrations result in a sale! That's profitable business! Write for Mu-Rad Franchise We are the exclusive distributor of the Mu-Rad Receiver in the states of Illinois, Indiana and southern Wisconsin. If your store is in any one of these three states, Mr. Dealer, write us today for details of our special exclusive territory proposition. Winter's here — there's need for haste! We also carry a complete stock of WESTERN ELECTRIC CO. GENERAL RADIO CO. parts. Write for details and discounts. Chicago Radio Apparatus Company Jobbers ot Good Radio Merchandise General Offices: 407 South Dearborn CHICAGO METALECTRIC SOLDERING IRON (The All-Metal Instrument) A Solution to the Small Soldering Problem of the Discriminating Assembler. Unbreakable Construction — Economical Operation on any Electrical Circuit — Interchangeable Tip. $5.50 From your dealer or write Post Electric Co., Mfrs. Dept. 509, 30 East 4Znd St. New York City mine the size and other details necessary to wind any given inductance. Turns per Linear Inch •o 0) w* <D Oj c 2 c a; a Size B. & Gaug S cc3 C T1 ° St too ■° 2 0 O Is 55 5 C ~ Cm 20.., 22.. 24.. 26... 28... 30. . 32. . 34.. 36.. 38. ..225. 29.. 36. ., 45. ., 56... 71. . , 88. . 112. ., 140.. 173. . . 25. . . 31.. . 37.. , 45. . . 54.. .64.. . 75.. .87.. .101.. .115.. 23. . 28. , 33. . 39.. 45.. 57.. 60.. 68. 78., 89. . 27. . 34. . 42. . 52. . 63. . 77. . 93. .112. .130. .151. 40. . .288 130 102 17? . 26 . 32 . 39 . 46 . 56 . 67 . 78 . 91 .104 .117 .129 It is a rare thing indeed to see a properly tapped coil; the usual practice of dividing a coil into taps having an equal number of turns results in large jumps in wave Percent Factor 4 1.057 6 1.087 8 1.116 10 1.147 12 1.178 15 1.226 2T0 1.308 25 1.394 30 1.483 The first tap is selected roughly, say , inch from the beginning of the winding. Figure 67 — Two methods of loading tuners with condensers Then, say, a 20 percent increase of wave length is wanted with each tap. 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