SERVICE MANUAL - American Radio History
Contents
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24. VAJ Aug WNL or Every Radio Enthusiast Should Read This Book By The Same Writer WRITTEN SO UNDERSTQOD Explainsthe theory and operation of Radio in plain E ng iia t lish About Radio 5 W Complete Thess to Make and Operat Radio Sets x MI Your Quia Now In Its 10th Edition PRICE FIFTY CENTS 96 Pages Fully Illustrated PETROLEUM IMPORT amp EXPORT CO New Orleans L M K THOMEN believe it is the finest specimen of plain English and technical information that I have ever seen I wish that more men could give us their thoughts as clearly and concisely as you have MR W R HERSTEIN Gen Mgr ELECTRIC SUPPLY CO Memphis Tenn I have taken occasion to read a great many books on the subject and I believe I can say without hesitation that your book is undoubtedly the best I have yet seen MR M P RYPINSKI In charge of Radio Sales WESTINGHOUSE ELEC amp MFG CO The book should meet a real need Postpaid on Receipt of 50c Stamps Check or Coin BERTRAM W DOWNS CO Publishers 2126 Iglehart Ave ST PAUL MINN
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38. T Volume 221 onec Iac ecce Mee 1 Aerials Loops and Counterpoises 8 Radio Batteries 12 Battery Eliminators Vacuum Tubes Tuning Units Common Questions and Answers How to Locate Trouble 2 The Station Finder 28 29 Directory of Broadcasting Stations in North America Classified Alphabetically by Calls 22 56 INTRODUCTION What to Expect From a Modern Radio Set ITH the transition of radio from the position of novelty We that of a home utility and with the steady develop ment of the art it has become realized that certain stand ards of reception must be met if the home radio set 18 to fulfill its purpose as it should The ideal radio set would probably be the one which would bring in any desired station at any time of day or season ex elude all others and reproduce the broadcast program with complete tonal fidelity and if desired full volume or intensity In other words the ideal radio set would have almost infinite sensitivity and selectivity perfect tone and volume without limit Certain causes largely natural have prevented the complete attainment of this ideal but nevertheless development in the radio art has progresscd to point where good modern instru ments scrve their purpose of entertainment and education fully as satisfactorily as a good motor car performs its function of transportation Perfection has not been an
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40. that will be best for your set As a rule a tapped coil with fifty turns and about ten taps will be right for all purposes The loop will pick up energy from the lead in without any physical connection Of course this will remove the directive property of the loop to some degree In the case of sets using outdoor aerial it has been found that under some conditions better results could be obtained by using a counterpoise in place of a connection to the ground The cus tomary means to a ground is by connection to water pipes radiators or rods driven into moist ground The counterpoise is really little more than a second aerial ordinarily nearer the earth than the aerial but not necessarily so The counterpoise is in sulated from other objects in the same way as the aerial itself It may be twenty to fifty feet or more from the aerial or it may be a fraction of an inch from it Some manufacturers are now making csounterpoise aerial wire which has a core of copper wire which is the aerial a composition insulating jacket and a braided wire covering over that the latter being the counterpoise The unit is erected just as an aerial with two lead ins one from the inner wire which attaches to the aerial post on the set and the other from the outer braided covering which goes to the ground ter minal In dry climates a counterpoise is usually preferable to a ground and the same is often true in other places where th
41. the probable cause of noise is to judge it by its sound Periodic noises occurring at regular intervals are usually external Noises in the installation are of three kinds those which go on steadily when the dials are not moved those which are heard only when the dials are turned and those which occur either when the dials are turned or when the set 1 jarred Noises which are heard when the set is not touched are usually caused by run down B batteries or A batteries sometimes defective grid leak will cause such noise Remove the grid leak from its mounting and note if the noise disappears If the cause is the grid leak the noise will disappear completely and not merely weaken 19 Noises which occur only with motion of the dials are tically always due to dirty or worn contacts between the moving plates of the condensers and the or to moving plates which against the stationary plates The cause of noises which occur either when the dials are moved or when the set is jarred may be the same as that just described or it may be that most difficult of all trou ble causes the poor contact This may be found anywhere and can only be located by trying all tubes in their sockets for poor socket contact tapping each tube separately for poor contact within the tube itself or taking the chassis out of the cabinet entirely and plucking at each connecting wire while the set is in operation seeking a p
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48. STATION DIRECTORY SERVICE MANUAL Written in Plain English Log and Station Finder COMPLIMENTS OF ROTH DOWNS MFG CO 1928 RADIO BROADCASTING STATION DIRECTOR Y and SERVICE MANUAL by BERTRAM DOWNS Sc Assoc I A complete list of Broad casting Stations in North America and a Guide for the location and elimina tion of trouble in Radio Receiving Sets BERTRAM W DOWNS CO Publishers ST PAUL MINNESOTA COPYRIGHT 1927 By E R DOWNS All Rights Reserved Printed in U S A INTRODUCTORY NOTE ADIO as a means for entertain R ment education and the dissem ination of general information has reached a high degree of de velopment Standard radio instruments them selves have reached a degree of excellence comparable to the pre cision work in fine motor cars However like any other mechan ism a reasonable amount of atten tion is necessary if a radio set is to be kept in the best of condition Sometimes a set will fail to func tion at all and it is seldom indeed that such failure is due to any fault of the set itself It is hoped that this booklet will be of value to the set user in get ting more pleasure from his set and in keeping it at fullest ciency under all conditions INDEX Page Introduction What to expect from a modern radio set 5 Sensitivity 6 Selectivity 6 Tone
49. Tuning Units HE radio set is adjusted or tuned to any particular station by means of condensers and coils of insulated wire In order to make the range of tuning continuously variable so as to include the greatest number of stations either or both the coils and condensers are variable in capacity That is the tuning unit be made up of fixed coils and variable condensers or fixed con densers and variable coils or variable condensers and variable coils Any or all of these combinations may be found in set Variability in tuning coil is commonly secured in one of two ways taps are taken off from the coil at regular intervals and nected that by means of a switch any desired number of turns can be secured the tuning coil may consist of two identical coils one of which rotates within or in close proximity to the other This combination is called a variometer When the movable coil is parallel to the other in one position the tuning value is maximum while half turn reduces the tuning value to approximately zero condenser is made up of sheets of conducting material separated from each other by some insulator In the case of fixed condensers it is common to have copper foil conductors and sheet mica insu lators A variable condenser due to mechanical requirements is somewhat different The plates are semicircular in shape and are made of aluminum or brass The insulator is air and the mov
50. able plates are so mounted as to permit them to sandwich hetween the stationary plates without touching One connection is made to each set of plates tuning coil should show continuous electrical circuit from one terminal to the other a condenser should 14 show no circuit or open circuit To preserve the good operation of a variable condenser frequently remove the dust from the plates so that there will be no danger of the metal particles or moisture in the dust accidentally making a conductive path between the rotat 7 ing and stationary plates pipe cleaner can be used advantageous ly in cleaning Common Questions and Answers 9 three tube set will receive 1 500 miles why won t a six or eight tube set receive 8 000 or 4 000 miles Because the sensitivity of receiving set is not the only faetor that determines receiving range If a broadcasting station can only send radio impulses to distance of 1 000 miles under normal conditions it stands to reason that no receiving set will pick up the messages from that station at a distance of 1 500 miles because in amp practical sense the signals will not be there to pick up at that distance By increasing the sensitivity of a set to weak signals you are at the same time increasing its sensitivity to static impulses There is tain threshold point where static will drown signals com pletely and any signals which are weaker than those wh
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52. ause the exposed area is insufficient and it does not reach moist earth at all Between these extremes of good and bad grounds there are numerous semi grounds which will never permit a set to work at full efficiency 17 4 Turn on the current to the set and note if the tubes appear to light up Due to the silvery coating it is hard to tel how bright they burn but if after a period of rest the tubes light up and visibly weaken it is a sign that the storage battery is discharged If the tubes do not light at all this either means that the battery is completely dis charged that the tubes are burned out or that there is an open circuit or poor connection in the filament wiring or filament switch within the set If all tubes light up but one it usually means burnt out tube or bad socket tact The surest way to check the condition of the storage battery is of course to test it with a battery tester or hydrometer With the current still turned on test the voltage of each B battery with a voltmeter The voltage of each 45 volt battery should be above 37 or the battery may be considered worn out One live battery and one dead one is just as bad as two dead ones With current turned on diseonnect one of the loud speaker terminals and then re connect it A very noticeable crack ling noise should be heard when the contact is made and broken If no sound is heard it may mean that the last tube is defective but it is more
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54. d probably never will be attained in either automobiles or radios yet both have unquestioned utility which has earned them secure places our every day life Practical perfection can be attained in most of the desirable Characteristics of radio set but there 1s one factor which has in the past as it probably will in the future limited the de velopment of radio This factor 13 atmospherics or static The term static has come to mean both natural and man made in terference and which of the two 18 of the greater importance depends on the location of the individual receiving set In out lying districts true atmospherics represent the main form of interference but in cities where there are street car lines bat tery charging stations power lines telephone exchanges etc these causes of man made interference often mals natural static unimportant by comparison 5 SENSITIVITY By sensitivity we mean the ability of set to bring in weak distant signals Strangely enough the present day receiving sets have little more sensitivity than the first radio sets They have however other characteristics the achievement of which has made sensitivity difficult to retain so that a modern set with sensitivity equal to that of the old three tuber is really an advanced engineering model Between good three five and even ten tube sets there 13 or dinarily little or nothing to choose in the way of sensitivity or distance gettin
55. e ground connection is not perfect As to the aerial itself the best length for broadcasting purposes is about 50 to 110 feet The day of the long aerial is past The lead in should be as direct as possible and should touch as few insulators and nothing else as possible There is a theoretical advantage in using stranded wire which advantage is seldom evident in a practical sense Theoretically the best aerial wire is that which is made up of a number of strands of enameled wire braided together There is absolutely no advantage in using more than one wire in the aerial although some people persist in erecting three and four wire aerials A four wire aerial is only of advantage when a transmitting outfit is used Lightning Protection With a loop or an indoor aerial there is of course no need for lightning protectors In the case of the outdoor aerial the condition is somewhat different During a lightning storm the aerial picks up a considerable amount of static electricity which should have a fairly easy path to the ground in order to protect the receiving instruments The danger is not that the lightning will strike the aerial and then set fire to the house if lightning strikes an aerial it burns up the wire before it gets to 11 the ground but the static charges coming from flashes of lightning some distance away are liable to do some harm if not provided for by a grounding switch or protector of some kind Any good lightni
56. ealers will sell these plugs on a trial basis Whenever practical however it is urged that a standard installation be used In order to make up for the inefficiency of the above make shifts it was found desirable to increase the sensitivity of the radio set itself to overcome the losses introduced at the start This has been accomplished mainly by the use of more and more vacuum tubes as amplifiers Three years ago a five tube set was a curiosity today eight and ten tube sets are common It was found that by increasing the sensitivity of the set the same results could be obtained with smaller and smaller aerials until finally it was found that a simple coil of wire about eighteen inches in diameter and with about ten to twenty turns of wire would serve as a collector without the use of a ground connection or aerial of any other kind This loop aerial is all that is needed with many sets of three to twelve tubes for receiving from distances up to several thousand miles The loop also possesses the property of receiving best from the direction in which it is pointed which is an aid in eliminating unwanted signals To operate a loop it necessary to use several stages of radio frequency amplification The most popular loop sets are those with plain radio frequency amplification or those with the super heterodyne feature By using the reflex principle the same tubes can be made to serve as radio frequency and audio frequency amplifiers a
57. ed wire I or wires to catch the radio impulses and bring them to the set With the widespread popularity of the home radio the erection of an aerial has been something of a problem particularly in dis tricts where there were many apartment buildings This condition has led to the adoption of trick aerials of many kinds and also to the popularity of many tube sets which will operate over long distances without the use of an outdoor aerial Substitute aerials include bedsprings fire escapes indoor clothes lines metal wires concealed behind picture mouldings and the like of these fulfill their purpose in some degree Still more effective substitutes are small aerials built in the top story of the buildings and patterned after the outdoor aerial These work in many cases nearly as well as the outdoor installation Aerial Plugs to be connected to the lamp socket are often as satisfactory as aerials although they sometimes fail completely the resulta being dependent mainly on the conditions in the wiring of the NONDIS 3112122234 D 40j 275 Duusjup 2 SNINIHOTY HOH OF 01 CZ 1 OGI OL 4 MIM VNNZLINY 2 802 NI AVI N ell IlIILRLILLILIZID 64117222 JINIAID house For this reason most d
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60. ete within year Although refinements in radio are constantly being made no set built in the past ten years has become really obsolete The underlying principles of radio do not change and set that does satisfactory service today will perfom just as well a year from today Changes that are being made from day to day are concerned more with the cabinet work and attractive workmanship of a set rather than with radical developments in design and principle Take for instance the Superhetrodyne which is frequently referred to as the latest development This set has been in use by advanced amateurs for six or seven years It has only sprung into popularity recently because peo ple have become convinced of the permanency of radio and are willing to pay for higher priced sets When radio was con sidered as a fad buyers hesitated to spend as much money on a radio set as they would on a phonograph Now that radio is established as an institution and there is a market for high priced sets the principles which have been known for years are finding expression in the production for the market My set has a range of 200 to 600 meters wave length How far does that mean it will receive The term wave length or wave frequency has no direct relation to the sending power or range of a sending set nor does it refer to the distance from which you can receive with a given receiving set To say that a station is sending at 417 meters wa
61. g ability This probably would not be the case were it not for static and atmospheric interference of similar character Any good three tube set will bring in signals so weak that they are no stronger than the ever present static level and greater sensitivity than this is not desirable nor will it be until some method of eliminating static is discovered Such amp method has been sought for a quarter century and ap pears as far from solution as ever today Therefore sensitivity as such 13 not matter of such importance as is often thought set possessed of the sensitivity of a three tuber of 1922 will give high degree of satisfaction But such a set is strangely enough not so easy to find as might be supposed The difficulty is to find set which has a high degree of sensitivity thruout the wave length band used for broadcast transmission The weakness of many five six and seven tube sets is that they will have fair sensitivity from two hundred to three hundred meters good sensitivity from three hundred to four hundred and have a decided falling off in effi ciency as the higher waves are reached The better sets of 1927 28 have not this undesirable weakness and this is the type the wise buyer will select if he is interested in distance and reliability SELECTIVITY The selectivity of modern radio sets leaves little to be desired This term refers to the ability of a radio set ander normal conditions to reject the signals f
62. ich can barely be heard will be lost in the static noise Conceive of gasoline tractor which would climb a 50 grade Could you by increasing the power of the machine induce it to climb a vertical surface The answer is obvious on such a grade there would be no traction nothing for the wheels to grip and the increase in power would count for nothing Too many persons look upon receiving range as merely a matter of getting an infinitely sensitive set without considering that to get unlimited range they must first develop transmitter with unlimited range and reduce static and interference to zero an impossibility 9 If I get good results with a 60 foot aerial why won t I get better results by adding more wires and making them longer A Because there is a certain aerial that is best for your set A shorter or longer aerial will result in diminished sensitivity Too long an aerial will absolutely prevent your receiving radio signals at all Remember the story of the lady who had a mania for patent medicines She acted on the supposition that if a little s good more s better and took four times the pre scribed dose The analogy is evident 9 If my set works well with 22 volts battery on the de tector as the instructions said why not use stronger bat tery and get better results 15 gt See answer above The same reasoning applies to batteries If I buy a set today isn t it liable to be obsol
63. in the accessories tubes batteries connections loud speaker aerial and ground rather than act ual trouble in the set itself It is not a difficult task to locate such troubles even for the novice and if the following instructions are followed carefully almost any case of trouble can be traced down to its source at which point the remedy will usually suggest itself 1 WHEN THE SET GOES DEAD Check over all battery connections With the wiring chart in your hand make sure that every connecting wire is at tached to the correct battery terminal and that connections between batteries are also right Then sandpaper each wire terminal and fasten it down tight so as to assure good contact Trace the aerial circuit from the lead in to the end of the flat top portion sure that there are no breaks in the circuit and no insulation leaks Trace the ground wire the same way Make sure that the ultimate connection actually is an electrical ground remem bering that to be a true ground this wire must make electrical contact with mass of metal having an appreciable area in intimate contact with permanently moist earth A copper galvanized plate three or four feet square buried deep in moist earth makes such ground city water works pipe or the casing not the pump rod of a deep well also fulflll these conditions half inch pipe driven three feet in the earth ordinarily does not make ground at all bec
64. ing the rest of the day using trickle charger the storage battery may be kept at maximum efficiency all of the time Care should be used however in following instructions which come with the trickle charger for it is amp piece of electrical appar atus and requires attention the same as any other apparatus of this sort The Battery has no connection with the lighting of the fila ment It serves only as a local battery to add strength to the incoming currents The incoming wave by acting on the grid of the tube serves as a trigger to release some of the energy in the B battery resulting in magnified current in the output cir cuit The detector requires one block of battery or 22 volts approximate y while the amplifier tubes take anything from 45 volts to 110 or more depending on conditions It is frequently advisable to test the B battery with voltmeter never with 12 ammeter Each 22 volt block should test 17 volts or more A new 22 volt battery should test 2114 or more and when the voltage is down to 17 the battery is about ready for discard The C Battery is found only in sets having amplifier tubes Its purpose is to give clearer reception and to reduce the drain on the Batteries At the same time it adds to the life of the tubes The C battery is usually about 1 volts when 67 volts B is used and from 8 to 6 volts when 90 to 110 volts B is u
65. likely to mean that the loud speaker cable is broken or the loud speaker burned out Borrow another loud speaker pair of head phones and connect in of the regular speaker Test the tubes The only visual test of course is to see that they light But even tubes which light are not neces sarily K and they should be taken to radio dealer and tested with the proper instruments which most dealers will do without charge test which is often productive and which may be made in the home is to borrow a spare tube of proper type one which is known to function and try it first in one socket and then in the next and noting if any change results This test will show up one bad tube but is of no avail if two or more of them are blocked since one blocked tube will paralyze the set If all of the above tests have been made and still nothing appears to be wrong turn on the set and grasp the first tube and gently move it about in the socket If the set comes to life for an instant it usually means a bent socket prong is not making good contact with the tube Try this with all tubes If the trouble is found in a socket the remedy is obvious 18 9 10 t If the set has a grid leak or resistance coupled amplifier these high resistances can be tested by moistening the thumb and forefinger slightly and grasping the resistors one at time between thumb and forefinger without re moving the resistor f
66. nd satisfactory loop sets may be made with as few as three tubes The natural thing might seem to be the combination of these ultra sensitive sets with an outdoor aerial but the advantage of both can be secured only to a limited degree for this reason There seems to be a certain distance beyond which no set can receive Of course the actual distance will be governed on any particular date by atmospheric conditions But although the super sensitive sets may bring in signals that are inaudible to the ordinary good sets the static and other interferences will also be amplified by the super set that the very distant signals are unintelligible though audible There is always some static in the atmosphere although you may not hear it Connect up a more sensitive set than the one you have been using and while you may bring in more distant stations you will usually also bring in static enough to blanket them But there is this much to be said for the use of an aerial with a loop set If the set does not bring in distant stations as well as others which use an aerial a small aerial can be erected and merely passed through the room in which the set is located the lead in being one or two feet from the loop This will usually increase the range of the set Or instead of leading directly to the 14 ground the lead in may pass through a small tuning coil or fixed coil and condenser Your dealer can give you data on the size of coil
67. ng protector approved the Underwriters will serve and an aerial so protected actually makes the house more safe than when there is no aerial If counterpoise is used it should be protected in the same way as the aerial Radio Batteries ATTERIES are used in radio to operate the vacuum tubes These batteries serve three different purposes and are named for convenience and batteries The A Battery is used to heat the filaments of the tubes The exact type of battery needed depends on the tubes used Most tubes take storage batteries while a smaller proportion require dry cells When dry cells are worn out they must be discarded and replaced by new batteries Time for replacement can easily be told by testing the cells with volt meter or by seeing that the tubes do not glow as brightly as they did when the cells were new Storage batteries with proper care will last for years They should always be kept filled with distilled or soft water so that liquid is well over the plates Hydrometers are used to test storage bat teries When the reading is less than 1150 the battery is dead and should be put on charge and kept there until the reading has increased to 1280 A trickle charger may be left attached to the storage battery all of the time charging at a very low rate 80 that the drain on the battery while the set is in operation is equalized by the slow charg ing dur
68. oorly soldered joint or weak riveted connection The microphonic hum which is more often noticed in sets with built in speakers is due to mechanical vibration of the tubes The detector is far more sensitive to vibration than any other tube and for this reason is usually in cushion Socket If the detector produces a steady hum which gradu ally builds up in volume until it drowns out the signals another tube should be put in its place and the noisy tube used in an amplifier socket Cutting down the detector volt age will usually help in eliminating bad cases of micro phonic effect The Station Finder GOOD many set operators would enjoy their receivers more they were able to find dial setting to get long distance stations and stations which they had previously been unable to find The chart given on the next page enables one to find the correct dial setting very easily Follow these directions carefully and you will add one hundred per cent to your set enjoyment 1 Tune in one five or six stations Keep note of the call of the station and the dial setting 2 Using the list given in the directory find the correct wave lengths for the stations you have heard 8 With each of the stations you have heard take the follow ing steps a Find the vertical line representing the wave length of the stations and the horizontal line representing the dial setting b At the intersection of these lines make a dot and
69. ore all sets use a detector many use both detector and audio frequency amplifiers and some use radio frequency amplifiers as well The vacuum tube consists of three essential parts enclosed in glass envelope from which the air has been exhausted In the cet ter is the filament which is heated to a point near incandescence by the A battery Next to the filament is the grid a metal ladder or screen and on the other side of the grid is the plate a square or tubular piece of metal i 18 The heated filament gives off electrically charged particles of matter which fly past the grid to the plate The incoming current which is impressed on the grid causes that element to regulate the flow of current from the filament to the plate so that the tube may serve as relay or amplifier weak current entering at the grid is increased by the local current emanating from the hot filament that the current leaving the plate is magnified duplicate of the current that entered by way of the grid This is the function of amplification The detecting of the wave or making it change to such form as will operate the phones is also done by means of the grid electrode which modifies the current passing through the tube The four prongs at the base of the tube are the terminals of the enclosed elements two for the filament and one each for grid and plate The prongs should be kept clean to assure good contact with the socket
70. os 099M iro WU At HOA VUIA AVOM LVOA HEBD 1930 ONES OD 88103 35 0140 S9JOjS eu YHON JO K amp 31819A U Usng T OUJ 331095 oadg IAA OD souor 9100 YNYD 48135 AWD SIUIL edurey OUT sepiosseooy OMY S PEA HOIA AL 1031940 ou 0002 058 0S2 OT 000 OSL 090T 008 076 OSZ 0821 092 029 00009 019 001 009 028 005 008 ous 0901 005 0221 008 001 OSTI os 0681 092 082 0081 035 088 001 OPII 0001 018 009 00 OSST 90009 089 SPEM 83149 oi HI
71. place next to the dot the call of the station c With a heavy line connect all of the points established in b This line should be straight or an even curve After you have found this line you will be able to set your dials to receive any stations whose wave lengths you know For instance if you want to listen to Station KMOX wave length 300 you should proceed in this way Find 300 in the list of figures at the bottom of the chart and follow this vertical line upward until it intersects the line established in 3 c Then fol low the horizontal line at this intersection to the left of the chart The figure here indicated is the correct dial setting to re ceive Station Best results can be obtained by enlarging the chart given to ap proximately fifteen inches long by twelve inches wide If your set has dials reading from zero to two hundred or zero to ninety change the horizontal ruling to correspond to the number of divisions on your dials i 21 0 10100 JO 3 3 06 081I 77 2010 uospuuunbo WHAM uesse 230H 00 Bo m EYYAM Ioouos OStT suog 700 V UBATIINS X AGAM ES 8330106 0001 0081 ow udesor 18 088 910 TAAN dul YULIA P
72. refore in choosing radio set the quality of the amplifier is of more importance than its status as resistance coupled transformer coupled or impedence coupled The tone of the best set can be disguised by poor loud speakers or poor batteries or tubes sure that your loud speaker is worthy of the set or it will be waste of money to buy good set VOLUME The volume of practically all good radio sets is highly satis factory but few people realize the intimate relationship between volume and sensitivity The cheapest set on the market will ordinarily give ample volume on local signals but it falls down when called upon to bring in weak signals with satisfactory intensity If a set is truly sensitive so that weak impulses make a reasonably strong detector action the volume of the set will take care of itself Don t judge the volume a set will give by its performance on local signals Test its sensitivity on distance signals or on locals with an arerial only four or five feet long GETTING DISTANCE No radio set will bring in any desired station at any time merely at the will of the operator tho the receiving in strument may be of the best type the broadcasting station T may not be using enough power to bridge the distance the static may be so strong that it drowns out the signals or it may be one of the days when the atmosphere appears dead and although static is light no signals seem
73. rom the mounting clips marked improvement in reception is nade when the resistor is so held the resistor itself is probably burned out and should be replaced by one of the correct value The above series of tests will in practically all cases locate the cause of trouble the experienced radio man the above offers nothing new to the novice it gives about all the simple tests which may be made case of trouble no satisfactory result is derived from these tests the novice will do well to call in the dealer from whom he purchased the set or some competent professional trouble man NOISY OPERATOR Noisy operation is usually though not always more diffi cult to overcome than complete failure to operate Obvi ously the thing to do in case of objectionable noise 1s first to determine whether the origin 13 in the set and installa tion or some distance away and then to seek the remedy It is more difficult to determine if the noise is in the set than might be imagined If the noise continues undimin ished when the aerial is disconnected this is evidence that the trouble is in the installation The surest test is to bring portable set to the same location and note if the same noise is heard To be of value the test set should use en tirely different tubes speaker batteries and even aerial Since interference noises affect all sets and ordinarily to the same degree test of this sort is conclusive Another way to estimate
74. rom undesired local stations and bring in signals from any station which the operator wishes to hear In this characteristic the modern set is in comparably superior to the earlier instruments The attain ment of selectivity however often has disastrous effects on the sensitivity of the radio set and it is only recently that design ing engineers have known how to combine both of these desira ble features in one set The prospective purchaser should 6 check the ability of his intended purchase to eliminate or tune out the locals TONE The tone of radio set depends on number of factors of type design and accessories and also largely on the reproducer or loud speaker The modern radio being an outgrowth of the radio telegraph or wireless inherited the amplifying equip ment ordinarily used in such telegraphy where amplification only was sought and retention of natural tone was of no im portance The amplifying transformers used as late as 1925 had the ability to amplify the middle tones well but bass notes and high notes were often lost completely The demand for natural tones brought out resistance coupled and impedence coupled amplifiers which provided practically uniform ampli fication of high and low notes but these types of amplifiers failed to completely displace the transformer because radio engineers have been able to produce transformers which dupli eate the results of other types The
75. sed The C battery be tested by a voltmeter and should be discarded when its voltage has dropped about 2096 or 2590 Battery Eliminators URING the past year a number of devices have been developed which transform house current into current which may be used in the radio set In the main these devices consist of 1 transformers which change the 110 volt house current into the proper voltage for B and use 2 rectifying units for changing alternating current to direct current and 3 con densers and coils to further smooth out the pulsations in the flow of eurrent so that pure direct current is produced The rectifying unit is generally an electrolytic cell or specially constructed vacuum tube Battery eliminators if properly designed and constructed give complete satisfaction Vacuum Tubes HE vacuum tube is the very heart of a modern radio set It is used in transmitting stations as well as in receiving sets In the home radio set vacuum tubes are used for two purpos s as detectors and as amplifiers The detector serves to change the character of the waves into electrical impulses which will operate the phones When used as an amplifier the vacuum tube either strengthens this phone current so that it will operate a loud speaker audio frequency amplifier or it builds up weak incoming waves to a point where they will operate the detector radio frequency amplifier As mentioned bef
76. to get through Broadcasting stations that are entirely out of range in the daytime may come in loud and clear at night The night range is approxi mately ten times tbat of the daylight range In winter when trees have lost their conductive sap when the air is dry and atmospheric electricity static is at minimum greater distances can be covered and more freedom from static interference is enjoyed If the above is new to you don t let it discourage your interest in radio for it is this very uncertainty that makes radio attractive How many fishermen would there be if it were only necessary to drop in the hook in order to pull out five pound bass One of the most fascinating features about radio is the fact that you can sit down at your set and listen to nearly any form of entertainment that you please from coast to coast and the next night you may hear an entirely different set of stations Of course the powerful stations that are near will be readily tuned in night after night at will but for real distant stations this is not the case Some radio enthusiasts find their pleasure in listening an hour at a time to the excellent programs most of them would rather listen to one number just long enough to find out the location of the station and then they are ready to turn to another content with tuning in as many stations as possible Aerials Loops and Counterpoises N THE past all radio sets depended on an aerial or elevat
77. ve length is comparable to the statement that a violin string is tuned to G of the pianoforte low power radio transmitter with maximum range of ten miles might be tuned to 417 meters while another transmitter with range of 1 000 miles could use the same wave length Like wise the violin string at might be heard from a distance of 200 feet a steam whistle also pitched at might be audible from two miles away The question How far will that set receive is seldom answered in an intelligent manner Probably this is because the question itself is somewhat am biguous It amounts to saying far can you hear the tone of middle C The answer to the latter is of course that it depends on the volume of that tone at its source whether the tone is emitted by a steam whistle or child s mouth organ whether the sound originated in a valley or from a hill top whether the listener was on country prairie or in the midst of city traffic noises whether the air was rare or dense humid or dry rather mediocre receiving set may bring in 16 signals from 1 000 watt broadcasting station 800 miles away but receiving set that will record the signals from 10 watter 100 miles away will have accomplished a much greater feat HOW TO LOCATE TROUBLE fails to perform as it should about 99 chances in 100 Wise a factory built radio set goes dead or obviously point to some fault
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