CENTS COPY / The Hammarlund Short Wave Manual 1935 EDITION

this manual will he found the constructional details on Generally speaking the larger the wavelength, the later in INwhat is, probably, the most carefully selected and compre- the day will best reception occur.The 16 meter broadcast hensive group of inexpensive short-wave receiver designs ever stations, for instance, are best during the morning hours. Those published in a single volume. operating on 19 meters come in well during the late morning The selections were made by the editors of five of the lead- and early afternoon hours.The 25 and 31 -meter stations ing radio publications of the United States, from among the usually are heard with maximum volume during thelate most popular and efficient designs described in their publica- afternoon and early evening hours and those on 50 meters tions during the past year or so.Then models of the re- are best received after darkness has fallen. ceivers were constructed and put through their paces in the The foregoing holdstritewithfewexceptions in North laboratory and "on the air" with the result that the twelve America.One of these exceptions is reception from Austra- designs presented here represent the cream of the hundreds lasian stations.These operate around 31 meters, yet are heard offered to the home constructor during past months. best by Americans in the early morning before breakfast (at Inasmuch as the most popular designs are the more simple which time itis evening in Australia and New Zealand). ones that combine low cost with efficiency, the receivers de- There are explanations for the conditions mentioned, some scribed here naturally fall in that class.The requirements of of them being rather involved.However, the important thing, the constructor who is looking for more advanced design are front the standpoint of the short-wave listener, is that these not overlooked however.Then, too, while the demandis conditions do exist.They can that the old practiceof sitting greatest for short-wave broadcast receivers, the special require- up all night for good DX reception is a thing of the past,and ments ofreceiversfor operation on the that practically any waking hour is a good amateur bands have not by any means been one for foreign DXreception, on one wave- neglected asis indicated by the fact that lengthoranother in the short-wave range. band -spread designs, and even a 5 -meter re- ceiver have been included in this group. Tuningashort-wave receiverisafar Having arrived at the final selection of more criticalbusinessthanisthe same receivers, the nextstep was toturn the operationonthe broadcast band.This is models overtothe experimentallabora- not due to any electricalpeculiarities in- tory for careful study to determine whether herent in the short waves, and is best ex- any of them could in any way be improved. plained by an arithmetical example. The fact that several of them came out of Assume that a receiver is capable of sep- this laboratory with improvements should arating stations which are broadcasting at not be taken as a reflection on the original frequencies10kilocyclesapart. Inthe designers or the publications in which the broadcast band of 1500 to 550 kc. there original descriptions appeared. The changes would be room for 96 such station channels. made mainly took the form of substitution If the tuning dial were properly marked off of more modern tubes or more efficient in 96 divisions, therefore, a station would be coils, with some changes in associated parts heard at every division on this dial to adapt them to these new units.In a few other instances changes which brought about a considerable improvement in Now, going down to the short -waves, the tuning rangeof a efficiency at a slight increase in parts costwere considered justi- single coil may be from 20 meters to 50 meters which means, fied and were therefore made. in terms of frequencies, from 15,000 kc. to 6,000kc.Instead ofproviding for96 channels there would be 900 such 10 - In some respects reception of short-wave signals differscon- kilocycle channels and with the same dial marking as men- siderably from reception of signalson the broadcast band tioned above, there would be 10 channels to every-division of above 200 meters.Perhaps the most prominent difference is the dial instead of only one.It therefore follows that in tun- found in the astonishing distances that can be covered with ing the short-wave stations the adjustment of the dial has to eventhe most simpleone or two -tube receivers.Itis no par- be exact to a small fraction of a division. A high radio tun- ticular feat, for instance, to hear the European stations and ing dial is one way of accomplishing this. others from remote parts of the globe quite regularly with such receivers. Undoubtedly the most practical method is found in the use of some sort of band -spreading system.The most common of Such distance reception is not limitedto the hours of dark- these is the one in which a small variable condenser is con- ness, as is DX reception on the broadcast band.In factsome nected directly across the regular tuning condenser,the small of the most phenomenal receptionisobtainedin the day- condenser being employed for the exact tuning.Take as a time. (Continued on nese page)

THE HAMMARLUND MANUFACTURING CO., Inc. 424438 West 33rd Street, New York, N. Y. Edition fully Copyrighted 1934, Iternmarinnd Mfg.Co.,Inc. Printed in U.S.A. 2 T he HAMMARLUND specificexample ashort-wave receiver Some points of ineffieiency are gener- withItroil plugged in, which covers the ally recognized.In the matter of insu- rangeof 20 to 50 meters mentioned above, lation,forin -tame, the average short- and employing a timing condenserof 140 wave enthusiast haslearned that nothing nimid. maximum capacity.UOtating this short of the lastis good enough.'this condenserthroughitsentirecapacity explains the almost universal preference range tulles thereceiver through afre- for Isolantiic insulated tutting condensers quency rangeof 15,000to 6000ke.,a and coilsockets.There are, however, span of9000 ke. or 900 10-kc. channel,. other factors which are less often con- Now,suppose a shuntvariablecon- sidered.Perhaps the most important ul denser of much smaller capacity isplaced these is the plug-in coil. ger., this 110minfd. condenser. Swing- A recent study of the low and medium - ing chi= small condenserthrough its en- mired plug-in coils available on the open tire range will result in arelatively small market showed them to have an average rapacity variation and therefore arelit. "Q" of approximately 100(at15 mega- tiN ely small frequeney range.With the cycles) whereas the "Q" of a perfect coil selection of the proper small capacity, for should approximate 200.Inasmuch as Instance, thefrequency range with the "0" represents the efficiencyofacoil smaller condenser may be only1/1.0th inatunedcircuit,theimplicationof as great aswith the larger condenser and SHORT WAVE FANS IN JUNGLES 01' these figures is obvious.In actual prae- in such a ease therewould be only 90 MALACCA tire.a"Q'.ol200is not obtainable in channels within the range of this con- A group of Jungle Dwarfs (theSakai) practical plug-in coils because of certain denser,tuning would become asnon- tuning in on a short wave regenerative inherent losses introduced by the metal critical as that in the average broadcast - receiver brought to them by Frank. Buck. prongs of the coil form, metal nearthe baud receiver. The variably condensers, sockei, coils, roilwheninpositioninthereceiver, etc. are all HAMMAID,lN.D. etc. When this systemis employed no ad- Hatesnarlmul has made high-grade plug- ditional coils are required and the only and a host that in coils for years, but these have been extra cost is that of thesmall condenser. modern superheterodyne beyondthepurseoftheaverageset '1'lle large condenser is employed to tune swear bythe regenerative receiver. acarefulin- saidfor both builder. however, after the receiver into the particular hand de- Thereismuch to be vestigation, the conelus' wasreached sired, say the 25 meter broadcast band, types of receivers.Where asinglere- boil,the that plug-in coils of excellent character- for instance, then the small condenseris eeiverisrequiredtocover istics could be prodneed to sell at a low employed to tune in the stations within short -waveandbroadcastbands,the price, especially as much of the research These stations will then he. superheterodynereceiverundoubtedly that hand. superior se- and development 'work involved in such spreadoutoverperhaps 15or21) de- has the edge because of its an effort had already beenaccomplished grees on the hand-spreaddial whereas lectivity onthebroadcasthand. For can in producing the coils employed in the they would fall within I or 2 degrees if purely short-wave work it safely be general types of Hattimarlund "Pro" receivers.The de- toned onthedialof thelargercon- said that either of these sign workWastherefore started and the denser alone. receivers,ifwelldesignedandcons new coils are now WIthe market at the strutted, is capable ofexcellent service. same price as ordinary coils.The forms Variable condensers, such as the Ham- Among those who "build theirown" employed in these new coils marlund Type MC -12013,areavailable the regenerative type of receiver isby far of XP -53, an exclusive Hamm:wham' pro- whichare especially intendedforpar- the most popular.Itis less costly, easier duct developed for this purpose.In this allel band -spread use.These are made to build, more easilyunderstood by the new insulating material thelosses have with the 2 condenser sections combined novice and more economicalin current been reduced to a point where it closely in a single unit but with separate shafts. consumption. Itsselectivitymay not approtwhes the low -loss eliartteteristies of The larger sectionattherearispro- equal that of a good superheterodyne, the most expensive dielectricmaterials. withaslotted forscrew- vided shaft but itis selective enough for most pur- Even theuseof artificialcoloring has alock is as great as van driver adjustment and nut for noses.Its sensitivity beenavoided,leavingthematerial a lot -king itina permanent position one, be used in many locations- enabling it to it has been adjusted to the desired band. bring in any signals that are above the natural light tan.In production, these The smaller front characteristicsarescrupulouslymain- set-Lion has a standard local noise level of the average location. tain.] andevenimproved by moulding shaft for control byafront panel tuning No mention has been made of either the X I'.33in a groove ribbed shape to dial.These condensers are principally straight tunedr.1.receivers, or those reducethe contact area between wind- used in "ham" receive,. employing superregeneration, because For those who are interested in a more neither one of these. rates serious con- ing and form to a minimum. detailed study Ilrauthat presented here. siderationforgeneral short-wave work 1s matters of utility and convenience, aninteresting discussion of hatutspread- between 15 meters and 200 meters. the coil formsare moulded with an in- ing methods,analyzing the various Super -regeneration iswithoutarival side shoulder which permits mounting methods in considerable detail,will he for use in inexpensive receivers to oper- the new liattimarlund type APC trimming foundinthe Ooctober, 1994issueof ate on wavelengthsbelow 10 meters be- condensers within the form, where they "Radio News." causeattheseextreme.frequencies are required forspecial band -spread or neither tuned radio-frcqueney amplifica- "fixed tune" purposes.A generous rim There is a considerable difference in tion or normal regeneration are useful. is provided at the top edge of the form, opinion as to what constitutes themost For the regular short-wave ranges, how- making iteasy to grasp, and a removable desirable type of receiver for short-wave ever, super -regeneration isgenerally con- wavelength index card is providedat the work.Thereare many who prefer the sidered too critical and too noisy to be top of the form, out whirl' the range 44 practical. the coilis printed.Where forms alone are purchased, for winding coils at home, If the signal voltage of a distant sta- these index earth; are left blankKOthat lk/IIis only in the neighborhood of a few millionths of a volt(asisvery often the case)atthe antenna it isobvious thatlossesorinefficiencyofantkind ntay make it quiteimpossible to hear that signal..Whether one's personalprefer- cute is for A SUper}leter.d)nt.,,rare- generative receiver, therefore, the most important single factor in the success of the receiver, outside of the choice of a good design to follow, will be the care POPULAR JAPANESE SHORT WAVE exercisedinselectingtheparts. Not onlyisitessential to provide a high de- POLICE ON SHORT WAVES TRANSMITTER greeof amplification, but it isequally The station which isheard the world importantthat lo-srsbe studioudy The elaborate short wave arrangement of over and is the goal of listeners. :.voided throughout the r.f. circuits. the Police Department of New York City. 1935 SHORT WAVE MANUAL

ceiver can dependon these coils covering theranges specified. Havingdeterminedtheapproximate ranges for the coils, there Were left the numerous other factors for study, such as the best fone factor, the best wire sizes and spacing, the best positions for the coilson the forms and the spacing be- tween windings.Most of these vary with frequency and therefore each individual roil representeda separate problem init- self. Space does not permit going intomon . detail hers, but the final proof of theex- cellence of these coils is found in the REMOTE SHORT WAVE WORK fart that the "0" (at 15 megacycles)era HAMMARLUNI) SHORT WAVE Sports and other remote broadcastsare found to exceed 150.This is believed to RADIO ON THE MORRISSEY sent to the main transmitter by portable he the highest value of efficienry obtain. Oscar Hammarlund (left) at the controls short wave equipmentas shown. Note the able in coils of conventionaltype. of a Ilammarlund "Pro" with Capt. Bob antenna-a loop of tubular copper Finally, theprong connection arrange- Bartlett lookingon, on board the Mot, ment is worthy of mention.There have rissey, the North Pole schooner. in the past beenno standards as to which the buildercan write in the range of the prong should bethe control -gridcon- finished coil. nection, which the plate,etc., in any but ceiver that receives toolittle attention isthe r.f.filterin The. development of the coil formwas, 4 -prongcoils;andeveninthesethe the plate circuit of of course, onlyone step in the process standardwas not definite.Now, through the detector.t isle,s a really good filter of design.The design of the windings the efforts ofsome of the manufacturers is used here ther.f.currents get into for the various frequencyranges repre- and of the magazine "Radio News"an at- the headphones or into the audio ampli- sentsthereal achievement oftheet, fier where they tend to increase body tempt is being made to standardize these rapacity effects,cause instability and nifty gineers.The first step in this workwas connections.The standards proposedto to determine the most practical frequency date have been adopted inthese Ham- even make itdifficult to obtain proper ranges for each coil-not in an effort to marlund regeneration. A filter consisting of two cover as much of the short-wave bandas chokesconnectedinseriesand with possible with each coil hutto determine Proper attention and forethoughtin .00025 ofd. by-pass condensers,one con- the requiredrange for each coilinits planning the layoutand wiring isessen- rn.etedfrom the junctionofthetwo relationship tial if a short-wave receiveris toprove chokes, to filament or ground, and the to the important short-wave efficient. station..Itisawell establishedfact This is particularlytrue of the other front the11 -plus end of the second that the greatest short-wavetuningeffi- parts involved in the tuned circuit of the choke to ground, will provide goodre- ciency is obtained when thevisit induct- detectorland ther.f.tubeifoneis sults.The chokes required for suchts-e ance is such that relatively used).The coil should be placeda dis- may heof Ior 2 millibenries induct:nice. capacity is requiredto tulle the coiltt. tance at least equaltoitsradius from The Hansmarlund type (CH -X)Sr- suit- the other parts suchas the tuning eondenser, :dile, are easy to wire, and ittexpensiNe. desiredfrequency.Theproblem, tube shields, metal panels, therefore,was to allocate the ranges so metal chassis, There are several factors whichcon- that asmany as possible of the important etc.Otherwise such metal11111,,,,12, will se- riously reduce the efficiency tributetosmooth andeffeeiieregen- frequency bands couldbe tuned at rela- of the coil. eration.The antenna seriescondi. .1,er tively low capacity values.The bands The coil, the tubeand the tuningcon- denser should,except for this limitation, employed inmost short-wave receivers aimed at primarilywere the 19, 25, 31 lla,a material itde- and 49 meter broadcast hands be placedas close together as practical influence because and the in order that all termines the degree of antenna coupling 20, 40, 80 and 160meter amateur bands. wiring of the grid and and therefore. the ansount of In the final coils all of these tuned circuits will lieas short as possi- energy ab- are tuned ble.Then this wiring should sorbed from the regenerative circuit by with highly favorable capacityratios. At be run in the antenna.The voltages(plate and the same tittle ample overlapis provided straight lines-avoidingright-angle bends, between as one would the plague. screen) applied tothe tube alsoitillts- ranges.The entire hand from etire regeneration, us sloes the plateIt)- 17.5 meters A metal panelor chassis should not be up to, and including approxi- depended pass capacity. mately,one third of the regular broad- upon as a conductor forr.f. cast band is covered with circuits.Allr.f. connections shouldhe )There "fringe howl"-itterrific audio a set of four made by coils,usinga 141) oust.Ifassonarlund means of wires, and these wire. disturbance whichoccursasthetithe condenser,as follows: all connected togetherat one point of goes into or outofoscillationisex- the metal chassisor panel. perienced, the conditionmay sometimes Coil 1-17,100 kc.to 7,30(1kc.(17.5 to 41 meters). be improved by du-- adjustments of the One part of theaverage short-wavere antenna or plate by-pass condensers. A Coil 2-9,200 kc.to 4,0001,c.(32.6 I1101.4, likely remedy, however, is to shunt to 75 meters). the headphonesor audio transformer pri- Coil 3-4,500 kc.to 2,000 kc.(66.6 mary (whichever is connected in the de- to 150 meters). tector plate cireuit) with a fixed resistor Coil 4-2,200 kr.to 1,100 ke.(136 of 100,000 ohms or higher. to 270 meters). For simple regenerative receivers the In addition antenna which will provide the best gen- to the above coils, a sep- eral results is the ordinary "I." ,irate roilisavailable tocover the Id - type with us -me of the broadcast band. This coil has a singlelead-inwire. Thisanaemia a range of 1,200 to 535 kc. or 250 to 561) should beas high and long as prarli,I, meters. the lead -its should be Lep' (dear of walls or other objects, theinsulation aundd I, Itis well to pointout here that the good, and ihe antenna and Icad-in should above frequencyranges were measured be one continuous length of wire with- under actual operating conditions, with out joints. thecoil If joints are necessary, they plugged into a typicalband- should h,carefully soldered. spread (parallel condenser) receiverand Special antenna systems have their ad- the antenna connected.If anything these vantages its many eases-but for the most ranges are conservative because thetest part arenotentirely practicalforuse receiver was completely shielded and the with any typeofreceiver in which the proximity of the shield walls wouldtend antenna is capacity coupled direct to the to reduce the coil ranges at the high- SHORT WAVING FROM AEROPLANES grid circuit of the first tubeasis the frequency ends.Thisis important be- A radio operator talking to his home case in the, great majority of regenerative valise itmeans that the builder of a re- office by tarty- of short.waves. receivers. 4 The HAMMARLUND A BoyScout's S. W.Receiver

set wasdescribed in de- THIStail in the September, 1934. issue of "Radio News." This receiver was builthe. Scout Robert Crockettof Pet ham, New York, and is agood example of a design which aims at ahappy combination of ef- ficiency and economy.It is as. sembled on u wood base and punch to avoid the expense of a metal chassis.Also, the dials used,costbutafewcents whereas dials of the vernier or drum types would add consid- erably to the overall cost.It will be noted, however, that the all-important parts involved in of the signal energy reaching the gridof the tuned circuits were selected with an List of Parts the detector with correspondingly greater eye forefficiency, as typified by the Haiti- IIAMMARLUND PRODUCTS volume at the headphones.Against this marlund lsolantite insulated condensers. C1-Midgetvariablecondemner,type MC - isthe factthat selectivity decreasesas The receiver employs relatively few 35S C_'. Midget variable condenser,type MC - the coupling is increased. parts and is a simple one to construct- 14051 easily within the ability of the novice C3-Midget vsriehlecondenser.type MC - The usualpracticeistoadjust the who contemplates the construction of his 250M series condenser (the coupling) sothat LI, La, L3-Set of 0 -prong plan -in thedetectorcartbe made tooscillate first short-wave receiver.Further,itis type SWK-0 one which, whencompleted, willgive RFC-R.P. choke. type C14-8, 8 millihenrios readily throughout all ranges.The an- plentyofenjoyablereception. Scout tenna absorption varieswith frequency, MISCELLANEOUS however, so that when coupling is loos- Crockett has succeeded in tuning in some C4-Acrovox micacondenser,type1460, 300 short-wave stations with it. .0001 eofd. tticil to the degree required at frequen- No radical claims are made for the set C5-Aerovon mini condemn,type1400, cies where absorption is highest,itis .001 tad. likelv to be. found unnecessarily loose at -.such as loudspeaker operation, etc., but 1{1-I.R.C. metalined resistor, 3 inegohms it will bring in the short-wave broadcast, 112-Yexley 30 -ohm rheostat tether frequencies where antenna absorp- amateur, police, aviation, television and SW-Cutler-Hammer, s.p.s.t. toggle switch tion is less. commercial 'phone and telegraph stations 1 Typo .30 triode vacuum tube 1 Sky 4 -prongsocket,type12orilam- From this discussion it is seen that the with comfortable audibility.European marlund Code 5.4 lnolantite socket adjustment of this condenser represents short-wave broadcast stationsare heard 1 Eby 0 -prong socket,type12or Hum. niarlund Code 5.6 luoluntite socket a compromise in most receiverswhere a with plenty of volume for clear head- 8 Binding posts, suimbly mocked for con- permanentadjustment is maintained. phone reception. nections as shown in rigitre 1. However, with thetypeof condenser Operation is also extremely simple, the used in this "Scout" receiver, this can be left-hand dial providing the stationse- readjusted to meet the variations in ab- lection and the right-hand dial thecon- a e sorption at different frequencies.It can trolof regeneration.The upper knob also be adjusted to provide loose coup- controls the rheostat.This is not used ling and therefore higher selectivity if in- as a sensitivity control but simply to terference is encountered, or to provide compensate for the normal drop as the closer coupling when tuning in extremely two 11/2 volt dry cells used for the file weak signals.In other words by vary- meta supply become aged. ing this condenser as needed, the selec- One feature of this receiver which is a tivity and sensitivity of the receiver are outof theordinaryisthe useof a under more completecontrolofthe midget air dielectric variable condenser operatorantibetterreceptionisthe (Cl)in series with theantenna circuit. result. It has beena common practice to em- ploya"trimmer" condenser of thecom- The front panel of the receiver is of pressiontypeforthispurposebut, 5/16 inch plywood with th inch plywood through the use of a variable air dielec- cleats screwed along the ends at the hack triccondenserhere,readjustmentis greatly simplified inasmuchasa screw for greater rigidity.The baseboard is of driver is not required, and the variation Yi inch hard wood. The front panel is in capacityisfar smoother than is the attached to the baseboard by means of easewiththecompression typecon- denser. wood screws,or with wood plugs and There isfrequentlyadistinct advan- glue;andisreinforced with two-inch tage in being able to adjust theantenna triangular wood corner brackets, glued seriescondenserreadily. Thiscon- to panel and baseat each end of the denservariesthedegreeofantenna receiver. coupling. Now, if theantenna is closely coupled to the detector circuit it tendsto Before mounting the front panelon absorbenergy and thus prevent oscilla- tion, even when the regeneration control the base it is well to drill the four holes iswell advanced.On the other hand, required for mounting the panel controls, close antenna coupling results inmore Fig. 1 otherwise the drilling operation is likely 1935 SHORT WAVE MANUAL 5 to impose a strain onthe panel.After asitis a common practice in one -tube the panel is drilled and is mounted on receivers.This puts less dependance on the baseboard, then all of the parts can the antenna series condenser as the sole be mounted in the positions indicated on coupling means and therefore involves the picture wiring diagram, Figure 1. less readjustment of this condenser. The balance of this circuit is so usual as to For the novice constructoritwill be eliminate any need for further discussion, ifthe circuit diagram more instructive especially as the values of all parts are of Figure 2isstudiedinconjunction given in the accompanying list of parts. withthepicturewiringdiagramof Figure 1.One can readily learn more by The batteries required consist oftwo attempting to wire the receiver from the No. 6 dry cells for the filament supply schematicdiagram. Thisinvolves a andone 45 volt battery of the type used little study but makesfor a more com- Fig. 2 in portable receivers,or two 22% volt C plete understanding of the receiver and batteries.Large size B batteries are not its circuits.If wired up in this way, the are of the 3 -circuit type.Coils having a required because the current drain of wiring can then be checked against the separate primary winding for the antenna the single -30 tube isvery small. picture wiring diagram to avoid any pos- circuit, as do these, provide somewhat This receiver can also be usedon the sibility of error. looser coupling titan is obtained when the regular broadcast band by addinga suit- As will be noted front Figure 2, the antenna is connected directly to the grid able larger coilto the short-wave coil plug-in coils employed with this receiver of the tube through the series condenser set.

plate supply either 90 voltsor 135 volts of B batterymay be employed, but the The higher value is recommended ifmaxi- mum audio amplification is desired. Sporting Twin The modeluses a wood baseboard 10 inches wide by 10% incites deep.The aluminum front panel is 10 inchsby 7 'THIStwo -tuberegenerativereceiver inches.The baseboard depthcan be re- I was described in detail in the May, ducedto 8 inches if space is not to be 1934, issue of "Short Wave Radio" by provided for the batteries. Robert Hertzberg. In assembling the receiver,at which This littlereceiver does notinany time Figure 1 should hestudied, the sense representa new development in tuning condenser (C1) and regeneration the short-wave constructionfield. In- condenser (C2)are mounted directlyon stead,itisone in whichthe designer the aluminum panel,as are also the on- combined well-known and accepted off switch and the rheostat principles to produce a set that is sim- (SW and .R1). ple and inexpensive to build, but which The Hammarlund short-waveplug-in the builder can depend upon for really coils will permit this littleset to tune throughout the entireshort-waverange worthwhile short-wave reception of all from approximately sorts of signals. 240 meters down and The circuit, as per Figure 2, employs whether the owner's interestlies in short- 2 tubes. One type -30 tube is usedas a wave broadcast, amateur, police, avaiution regenerative detector with a condenser, or commercial reception-or all of these -he will be gratified bythe resultspro- C2, to control regeneration. A -33type duced by this receiver. pentode provides one stage of audioam- plification, this tube being coupledto the detector tube by means of a transformer. List of Parts HAMMARLUND PRODUCTS CI, C2-Midget variablecondensers,type REAR VIEW MC.140M OF PANEL. C2 C3-Equalizer condenser,type EC. -35 NI 1 RFC-R. F. choke, typo C11-8 ' 0 L-Set of 4 -prong, 2.eircult plug-incoils, CI type SWK.4 1lilt, S-Isolantita 4-prong socket,type 5-4 MISCELLANEOUS PARTS Both of these tubesare of the2 -volt C4--Aerovox.type1460usedcondenser, .0001 mid. RI filament type. Two ordinary No. 6 dry cells may therefore be used RI-Elortrad 10 -ohm. rheostat IP to supply 112-1.R.C. metalised resistor, 3 megohrns RFC the necessary filament current.For the ail SW-Toggle switch, s.p.s.t. .88.. GND. T-Thordarson audio transformer, type R- 260 V1-13by 4 -prong tube socket, type12,ar llammarlund Code S-4 Isohntite socket V, , ©r p j..) V2-Eby 5 -prong tube socket, type 12,or AB- ,,,,,0 .1 Ilammarlund Code S-5 Isolantite socket { \72 A- V. -33 1. Eby 5 -gang strip (screw terminals) /C4-,('' .4... ANT. ii --r Eby ctrIP (screw terminals) _ R2 r G 1 Eby 2 -gang strip (tip jock terminals) IM24U 1 Kurs-Kasch vernier dial (largo) 6+90. 1111 COIL r r 1 Aluminum panel10 inches by 7 indict. TO 13SIC SOCKET VI -30 (cut and drilled-Blan the Radio Man) C -s' 1 Wood baseboard,10inchesby10Ma 7043.5V. inches, 84 inch thick TOPVIEW OF BASEBOARD A+3V. A-311. 13+22.5C-8 8+90 8Metalbushingsforelevatingterminal 8- C+ 7045V. luau TO 135V. strips, etc. Fig. 1 Fig. 2 6 The H A M MARLUND The Dragnet (2 Tube S. W. Set)

DESIGNED by the technical staff of "Radio News," this receiver ,Gas originally de- scribedintheAugust,1934, issue of that publication. The "Dragnet" employs two of the latest type, of 2 -bolt tubes and is designed to take full ad- vantageoftheir superior fea- tures. Although only 2 tithes areemployed. 3 -tithe results are obtained because the type -19 tubeisadual purpose type having two triode sections en- closed within one bulb.One (litho, or when on the edge of oscillation, of these triodesis used asa regenera- cannot be radiated and cause interfer- tive detector whiletheother provides encein neighboring receivers.In other List of Ports strictly a "non - one stage. of audio -frequency amplifica- II 1v1 VIA RI.UND PRODUCTS words, this receiver is tion which aids materially in building C. 2 -M irlgetvariablecondenser,type MC - blooper". weak signals up to good headphone vol- 1.10M The completecircuit is shown in ume. The other tube, a type -34 variable - ItEC-R.F. choke. type C11.8 Figure' 2.Itwilllieof interest to fol- mupentode, is used inat.untuned stage 2t -el. ntite Lprong sockets, type 5-4. low this through from antenna to head- 1 1-slan tile 6 -prong locket, type 5.0 of radio -frequency amplification. 1.nlantiteplug-incoilforms,1 -prong. phones. This r.f.stage serves a threefold pur- type CF -4 The resistor Ill, condenser CS and re- pose.First,it provides an appreciable MISCELLANEOUS sistor 1.14 arc the elements of the resist - amountofr.f.amplification. Itisa CI, C7--Aerovos. type 1467 .00025 mid. coupling system through which the kiwis. fact that for maximum amplifica- C3. CO-Nerovon type 1407 .0001 'OA. audio -frequency output of the detector C4,CS. C9-Aerovt»c pigtailby.pass tion from tithesOf this type they must deniers, .1odd.. 200 volts is applied to the grid of the audio sec- work intoahigh impedance load.The Ctl-Aerovox by -past,rondenscr,.5 tion of the -19 tube. best satisfiesthis condition mad., 200 volts The parts used throughout weresc- Itt-I.R.C.mei:divedresistor,ito -Ignite.. is a tuned circuit. Itis this type of eh -- V2 watt hemed for their high efficiency, a feature cult, consisting of the coil LI and con- R2-Centralab potentiometer, 100,000 ohm. of the greatest importance, especially in denser C2 thatis employed in the "Drag- 113-1.R.C.metalized reeistor 10(10,0011 ther.f. and detector circuits.Thus the ohm, 1/2 wait net". Also, under actual measurement It met al izedresistor. 1 nteguln, coil and tube sockets are of Isolantite, it was found that the iominon practise of V watt as arealso the forms upon which the using a metalio.edresistor,1500 ohm, plug-in coils are wound, the insulation of resistor input did not product, watt nearly as good results as the choke, RFC, metallized resistor. 15,000 ohms. the tuning rondenser and the, insulating nordidchokesoflowerinductance watt forth of the r.f. choke. Even the antenna R7-1(axley ..lunior" rheostat.11) ohms Connection terminal takes the form of a I millihenries) equal the one employed. sW-Toggle switch, d.p.s.t. The second advantage of the r.f. stage 1 Karr -Kam+ vernier dial, 2% inches tiny porcelain stand-off insulator toin- is that it serves to completely isolate the 1 Midget porcelain stand-off insulator sore againstlosses. To reduce coil losses antenna fr the regenerative detector Insulated 'phone tip jack, to a minimum, the roil socket is mount- circuit and therefore eliminates absorp- 1 Binding post( for ground terminal ) ed on bushings which elevate it approxi- 1 5 -wire hatter,cable, length optional - tionof regenerativeenergy by the :An- 1 Rubber grommet (for protecting battery mately I inch from thechassis.Half tenna, thus making regeneration much cable where itpasses through rhassis I hid]bushingsare suppliedwith each 2 I. inchhakelite. knobs(far 112 and more constant and easier to regulate. 1171 Hammarhand socket.Inasmuch as th, The third advantage isthat withthis ,41111110, 10 inches tie7inches, are notrequired for the socket of the t _10 inches by r.f. tube acting asaharrier, ther.f. en- and aloositturn ellaSSi., -34 tube, two sets are used for mounting, Inches by .1. inchhighMilanthe ergy generated by feed -hackinthede- Raclin Man). the coil sueket.The socket for the type tector tube when in an oscillating eon- -19 tube is elevated on the bushings sup -

THESE NUMBERS COINCIDE ON TOP AND BOTTOM VIEWS 5 INDICATING CONTINUOUS CONNECTIONS

GNP C8 BOTTOM VIEW

Fig. 1935 SHORT WAVE MANUAL plied with it. prongs and therefore no drillingisre- The coils for this receiver are home- quired.Also, theyare equippedwith wound and the complete winding data knobswhichhavecardboardinserts, will be found herewith. The Hammar- under transparent windows,on which the hind Isolantite roil forms employed offer wavelength range of rash of 111e coils1.1111,. numerous advantages, in addition to that be marked. The correct internalconnec- ofhighefficiency. They are supplied tions to the fourprongs of each coils are with plenty of holes through which to shown in Figure 3. earrythe ends of the windings tothe COIL DATA Range 1,1/,2 Frequency Wavelength No. 1- 6 6 18300.10710 15-8-28.0 No. 2-10 7 13040.667023.45 No. 3-18 9 7140-385042-78 Fig. 3 No. 4-30 12 4170-226072-133 No. 5-50 20 2380.1220 126-245 The switch SW is of the double -pole. - No. 22d.s.c.wireusedforLI, single -throw t)pe and cuts off both the A ranges 2, 3, 4 and 5; No. 28 tl.s.c. for and 13 batterie,thelattertoprevent range I. slow B batter): leakage across R3 when No. 28 d.s.e. for all ticklersI L2). the receiver is not in use. LI and L2 separated inch, all The panel and chassis each consist of ranges. 7 inch by 10 inch aluminum sheets. The LI windings spacedto occupy 1l/2 chassisisbentatright angles,linch inches for roils1,2 and 3.Close from the Front and 1 inch front the rear wound for coils 4 and 5.All ticklers edges, making it10 inches by 5 inches Fig. 2 close wound. by 1inch high.

It will he noted that there itre two an- tennaposts. Number oneisintended for use with an antenna of only a few The feet in length, or where an external an- tennaseriescondenserisemployed. Argonaut Terminal number two is used where an antennaof normal proportionsisem- TBIS 2 -tube, dry -cell operated receiver ployed. was describedinthe August, 1933, The flatinnarlundfourprongshort issueof "Short Wave Craft."At that wave coil kit will provide excellent cov- time it received an enthusiastic welcome erage,and if broadcaststationsare from short-wave constructors,one reason wanted, an extra coil will afford equiv- beingitsrelativelywidespreadlayout alent results. which simplifies especiallygoodreceiverforthebe- of Parts ginner. 111,114ARI.1iND PROD! t:T, It employsa type -30 tube as a regen- erative deteetor, with regenerationcon- Cl-Variable condenser. 131. MC -1,021 REC-11.F. ehoko, type Eki-x trolledbyvaryingtheplatevoltage 2 ',infantile snekets, 4 prong, typo 5-1 through the medium of the potentiometer L-Set of 4 -prong2 -circuitplug-in R2. The audio stage also employsa type type SWK.4 -30 tube which is transformer coupled to 511SCE1.1..\7.1.0( the detector.'Phis tube combination will r tenser, .0001 nail. provide good headphone volume C.8-See tex. even nn E4-Cornell-Oubilier condom:ex .00025 Dad. weak signals. C3-Cornell-nithilierpigtailliy-passcon- The antenna series condenser, C3,as denser,.1 tufa. shown in Figures 1 and 2, is quite novel 111-1.11.C. met:divedreoistor,3snegoltots R2-Eleetrailpotentiometer.typeR1-212. in its construction.Instead of using the 100.000 ohms usualequalizertype,adjustablecon- it:i-Electradpotentiometer,typeR1-209, denser here the designer made hisown offered by this kinkis the fact that it 2C ohntv condenser by winding 14 turns of T-Thordarson transformer, Type T-5736 insu- roots nothing.Actuallyitis cumber.ionte. I Knrr..Kaseit vernier dial(large) lated hook-up wire tightly arounda 11A to adjust and itis suggested that the con- 1 Aluntitm lllllpanel. 7invitesb,12 incite, inch length of bus bar, the hook-up wire structorwillsave time and trouble by 10 gauge. and 1 :amain um 11% inches by8 inches by 1 inch and the bus liar each formingone plate substituting aIlammarbind type EC -35 high tillan the Hatlio )tan) of the condenser.The capacity ofthis equalizer condenser here, itscost being 1 Eby2 -gangterminal:trip(cerewter- condenseris variedeither by slipping on1,- minals/ a few cents and easily justified by 1 Eby 2 -gang terminal strip(tip jacktcr- he coil partly offfluebus liar,or by the greatervonventence and permanency tt i tt als) unwindingturns.The soleadvantage of Ajustnient. 1 Eby5 -gangterminalstrip(screwter- - As) 1 Eby realer typoI-prortg midirt or ilum- marhind Code S-4 Igolontite socket 13+4.5 TO 90V.., B- At A-. air. 1 D.P.S.T. toggle switch. ° - ...,_

IL _,,.....,. r=r-... , ..,,,___: R3 0 n 1 , p RFC C3 Vo_..git.' (SEE TEXT) .;p P A IMII , ..i.... ti 1 41(trn ,I 4 1.11 o 0 o e 0. ens, '1,. F::: OM ,'4 F T to -SOCKETKET Ri VI VI 'COIL 14.1 -30 SOCKET g ' '0' ..i.ft. R2o No.2 R3 TOP VIEW Nt BOTTOM VIEW Fig. 1 Fig. 2 The HAMMARLUND

Send for Catalog for Complete In. on. AranuP1 all II.4MMARLUNDproducts PR( Manufactured by HAMMARLUND MANUFACTUB1

Improved HAMMARLUND MidgetCondensers New HAMMARLUNDLow Loss Coil Forms The marked efficiency ofHammarlund con- and Short Wave Plug-in -Coils densers at ultra high frequencieshas been at- tained by extensive research inmaterials and These attractivelypriced coil forms art design, constant experimentationand careful made of XP -53dielectric, a remarkable workmanship, plus years of experience. new lossinsulatingmaterial.Rugged. lsolantite insulation reduces dielectriclosses durable and most important,extreme, to a minimum, assuringmaximum and uni- effective, for XP -53 losses areextremel] form efficiency underall conditions of tem- low. Its amber color isnatural...nt perature andhumidity.Wide bearings, front artificial coloring to causelosses. The coil and rear afford extra good contactwithout ob- proportions provide mostpractical forn jectionable inductive reactance.Non -corrosive, factor. The forms are groove-ribbed foi Type NC soldered brass plates eliminatevibration and air spacing ofwindings. There are also effect lowest series resistance.Shafts 1/1"in flange grips, and neat meterindex in. diameter, extending 5/16" beyond rearfratne serts, for wavelengthindications. Anothei to facilitateganging.Individually tested for Type SWF clever feature of the form is athreader breakdown on 500 volts A.C.11/2" bakelite shelf, molded inside, to permitthe mounting of a trim knob. Available from 20 mmf. to 325mmf. using or padding condenserfor tuning the coil to a fixec Code MC.140M ...$2.50 frequency or for bandspread arrangement. Code SWF-5(5 prong) .35 Cede SWF-6(6 prong) .40 These Double Spaced Midgets have wide Hammarlund Short Wave Plug In Coilsprovide max spacing, special bearings, andlsolantite, mak- imam signal strength,and greatestselectivityonal ing them particularlysuitable for ultra short hands. Extensive laboratorywork results in practicall: wave receiversand transmitters.Midline or perfect design of primary, secondaryand tickler, coup semi -circular plates in 20, 35 and 50 mmf. sizes. Double Spared ling and overlap. Wound on low loss HAMMARLUND Dual and BandSpread Midgets X P-5 3 dielectric LikeHammarlundSingleMidgetCon-Hammarlund Plug In densers, these duals incorporate intheir de-forms.Yourcoils sign every requirement of a high qualitysmallcoverthe en t i r e size two gang condenser.Their rigidity, lowrange of1.7 to 270 losses and careful construction affords greatestmeters, andonly one electrical and mechanical efficiency in all typesadditional coil is re- of short wave receivers, using two gang tuningquired to cover the condensers.The entire condenser is built onbroadcast band. Sec- a strongIsoluntite base, including a shield plateondaries of the17 to between the stators.Other specifications are41 meter and 33 tc the same as for the singles.Made for single75 meter coils are of Dual Midget hole panel mounting.Overall length behindheavysilverplated the panel -31/4". wire to reduce skin There are double spaced duals for ultra high resistance losses to SWK Set of Coils frequencies for transmitting and receiving. minimum. The sec- The Band Spread Midget Condensers are de- ondaries of the other signed for use as band spread tuning con- coils are of silk covered copperwire. The 270 to 56. densers for short wave receivers or amateur meter coil isof bank -wound litz. band frequency meters, and are extremely ef- Code SWK-4 (Kit of four, 4 prong, 2winding coils, fective. The tank section may be set and locked range 17 to 270meters)...... $3.00 permitting the tuning Code SWK-6 (Kit of four, 0 prong. 3winding coils, at any desired capacity, range 17 to 270meters) . 3.75 section to spread narrow frequency ranges over Code BCC -4 (4 prong, 2 windingcoil for broadcast the entire dial, regardless of the range of the band, range 250 to 560 meters)...... 1.25 band, or the coils used. Code BCC -6 (6 prong, 3 winding coil forbroadcast Code 51C4.2013 $3.00 band. range 250 to 560 meters) 1.50 HAMMARLUND Star Midget Condensers Air Padding A very popular low priced midgetfor set New HAMMARLUND builders, experimenters and laboratories.There Condensers are types forreceiving, and transmitting, for shortwavetuning,regeneration,antenna These are high quality air di coupling, verniers, etc.Light in weight, strong electriccondensers for u s and compact in construction, smooth asvelvet whereever space is at apremium in operation. Low minimum capacity,low loss They will maintain constant es natural Bakelite insulation, non -corrosive alu- parity under any conditions o minum plates.Easy single hole mounting, 1/4" temperature, humidity orvibri Star Midget shaft, 5/16" bushing, 1" bakelite knob.Size Lion. Highest order of efficiene 1-9/16" wide by 13/high. Depth behind the adapts them particularly to shot panel front 11/16" to 1%" depending on capacity. Available in sizes wave and ultrashort wave wort; from 15 mmf. to 140 mmf. Air Padding Condenser Overalldimensionof 101 Code S31.25(25mmf.) mmf.sizeonly1-7/32"b Code S31.100 (100 mmf.) . 1.00 15/16" by 11/2" high. Isolantite base. Soldered brass rc 1.25 Coda SM-140 (140 mmf.) . - tors and stators.Sizes range from 25 mmf. to 100 mmf 1935 SHORT WAVE MANUAL 9

All prices shown, hereare EC/S/0/Viarluncl list prices of parts used in /DUCT S sets described in this manual. G CO., Inc., 124-438West 33rd Street, New York

HAMMARLUND Isolantite Coil Forms New HAMMARLUND MEX and Standard Midget. and Sockets Equalizing Condensers These Coil Formsare of extruded The type MEX condenser isan extremely small Isolantite. Their low losses andeffec- adjustable low loss condenser expresslydesigned -1",e..5) tive stabilityguarantees efficient high for trimming RE coils, but useful formany other frequency results undeall conditions. purposes. So light in weight, as to permit its being Equipped with convenient blacken- self supported in wiring. The base is Isolantite. ameled wooden handle witha flat top, Dielectric is Mica, and spring plates of phosphor in which isa removable paper disc bronze.The size of the base is Vs" by 3A". VEX for writing in frequencies.A celluloid MEX (range 3 to 30 mmf.). s .30 disc protects the paper, a spring ring The standard Equalizing Condenseris a littlelarger holding the disc in place.Surface is thanthe MEX, and is also for neutralizing,balancing and trimmingpurposes. "non-skid," eliminating troublesen- It countered in winding is also useful for adjusting multipletuned circuits organg con- on slippery sur- denser units. Adjustment of thecenter screw faces. The numerous holesprovided in the form, make drilling provides gradual capacity changeover a wide unnecessary. range. May be attached directly to binding post The form is11/2"in diameter and of socket or condenser. Mica dielectric, 21/2"longexclusive phos- of knob and Type CF phor bronze flexible plate and prongs. Made in 4, 5 and 6prong bakelite base. types to fit standard sockets. Size of base-PA" by 11/16". Type' CC EC -35 (range 3 to 33 Data.)...... $.40 Code CF -4 (4 prong) ..$1.00 Cede CF -5 (3 prong) HAMMARLUND Standard and MidgetIsolantite Code CF -6 (6 prone) 1.00 R. F. Chokes Lowlosssockets The Standard Choke is particularly de- --,....."'-'77/717,T4r- signed for shortwave, and ultra short ® are just as importantwave receivers and transmitters, butis as low loss coils orequally effective within broadcast band. condensers.IntheCompactness permits mounting in isolated HammarlundIsolan-positions well removed fromstray RE fields. Four windings, moisture proofed, tite sockets, low lossand carriedon Isolantite spool. Protected Type C11-0 Type is eoznbined with lowby radio frequency lacquer and cellophane covering.Inductance cost. Constant resis-8 mh; DC resistance -70 ohms; distributed capacity -3mmf; 125- tivity and perfect contact eliminates noise. milliamperes. Choke is 13/8" by Vs". The sockets have glazed tops and sides. The side grip- Code C1143 $1.10 ping contacts are rust proof. They can be used for sub The Midget Choke is invaluable foruse where space is at a prem- panel or base mounting. Made in four, five, six andium. Its tiny size, and lightness permits itto be supported by its own leads. Five universal wound pies mounted on a 3/4" Isolantite seven prong styles. They all are 21A" long, and 1%"core, with coils impregnated to insure ruggedness and minimize wide, with standard mounting centers of 1-27/32". atmospheric effects. Tinnedcopper wire leads, secured to Isolantite Code 5-4 (4 prong) .8 .60 core with metal end caps. Length acrosscaps- Code S-5 (5 prong). .60 I1/2 ". Diameter-% ".Inductance -2.1 mh; DC resistance -35 ohms; capacity -1muff., . 17') Code S-6 (6 prong). . .60 125 milliamperes. Type Cith eux

HAMMARLUND Flexible Couplings HAMMARLUND Triple Grid Tube Shields This coupling permits tandem opera- The complete isolation afforded by this shield permits tion of any number of independent units full use of theenormous amplification possibilities of without requiring exact shaft alignment the new tubes. -a great convenience and time saver. The condensers are insulated from each A special drawn in neck completes the shielding be- other, allowing instruments ingang to be tween the control grid and the plate, and a removable operated as independent units. Bakelized top is used to entirely shield the control grid cap. The canvas,withbrassbushingsfor1/4" body, cap and base are all made of heavy aluminum and shafts. Four rust proofed and hardened designed for maximum cooling. Measures 43/8" high by steel screws provide againstany shaftslip- Type FC ping. The overall diameter is 1%". 15/8" diameter. Mounting center is standard -1-27/32'.

Code FC . $ .60 Code TS -50 . " 5.40 Type TS -50 10 T he FIAMMAHLUND APowerPack for S. W.Receivers

powerpack illustrated in TIIEthe aceompany ingphotographs and diagram, is onewhich is to be ileseribedindetailin one of the forthcoming issues of "Radio outputvoltageobtainedwith was thedays News." Specialpermission choke inputisconsiderably lowerthan obtainedfrontthis publication to that obtainablewith capacity input.This publish this advanceinformation is really an advantagebecause while few because itis felt that thisparticular short-wave receiversemploy more than designfills a long felt needfor a 200 volts on theplatesitis (Mesh to really good powersupply unit de- obtainpowertransformerswhichwill signedespeciallyforusewith provide such lowvoltage.The normal short-wave receivers. aridleast expensive powertransformers Many present day !Dowerpack, provide ana.c.voltageof 300-330each proveentirelysuitablefor us4, sideof the center.When a condenser with non -regenerativereceivers, or input filter isused with these, atnormal ithreceiversdesignedforthe drains, the d.c. voltage outputis usually broadcast band only.But when used List of Parts in excess of 300volts-a value quite ex withshort-waveregenerativereceivers cessiveformostshort-wave.receivers. troublesomein C2-Aerovox type1;1;electrolytic con- these units' hum isso denser. 2 -section, 8-8oad.,430volt,, Thus the use of chokeinput permits em- manyinstances astoseriously mar re- /1.e. ployment of the least expensive typeof This is particularly trueif the Ca. C4,CF,--,10rova.type GC1: electrolytic Eeption. condemier, 3 -section,.1--1-1 tad.. 430 standard power transformer. receiver is maintainedin an oscillation tl.e. The power park describes.'here pro- condition for reeeptiooof c. w. signals. vides 229 volts the. at a currentdrain of Such trouble is usuallytraceable to the (T7AT' in addition it includes 11.t17-'t-I.102 25 milliamperes. inthe inelti,ion of an inadequatefilter Ii EC -41: lllll Harland type 1:11-Xr.f. choke a 6 -voltfilament winding rated at 1.3 am- powersupply unit.It may be due to 8--Electrad 30 ohm center -tappedfila- which will supply the filamentsof the use of ment resistor peres skimping on capacity, or to 112-Electrati Tr. volt oltanc 1:0- up to5 tubes of the 6 -volt type.In the only one choke, or perhaps2. chokes hav- C-200, 20,0noohms,30 with 3 particular model shown herethe voltage ing insufficientinductance. adjustable intermediate taps with3 adjustable 12 dividerisprovided Another common sourceof trouble is 1 Eby1 -prone tube socket. type supplying the high voltageand in unstable operationof there- Eby 11-111011,4 tubesocket. type 12 taps, thus found I in,.6 -prongcable plan, malc two intermediatevalues, all variable. is one employ- length) ceiver, particularly ifit I Six -conductor cable lof rent:fret( r.f. stage ahead of the re- SW-Toggle switch, Another featureofthis power pack ing a tuned former, typeT. Such instability-is T-Titordarson power sr:MS which should notlie overlooked is the generative detector. 3.172 r.f. filter consisting of the r.f.choke RFC, often due directly toinadequate by-pass I 'type -80 rectilir, tube C6 which has a capacities across the variousvoltage taps Si'.foot lint, cord with plug and the mica condenser Robber grommet. !/.:]; inch( for power cord capacity of .01)6 mfd. The purposeof this in the powerpack. bole in / chassis(shaped and tilleris to avoid the tunable hum some- Both of thesetypesof troubles arc I .\I oteli lllintor steel troublesome in short-wave sets. eliminatedintheunitde- drilled-Blatt the Radio Man) times so effectively made in this scribed here. Two sizablerhokes are in- Alterations may readily be eluded in the filter, anti a total of 16mfd. Prominent after thefit st choke :whereas powerpark to meet the requirementsof for thefilter capacity.In addition,a a,endenser eonnectedahead 'ofthis :my particularreceiver.For instance,if eapaeityof4mfd.isprovided across loads. Ilv choke is N111,,i,ted to abnormal itisbuilt for use solely with acertain eachofthe output voltagetaps.'1'h, eliminating the input condenser,there- high voltagetothefilterisobtained fore. the strain on thecondensers is ef- receiver which containsits own voltage throughacenter -tappedresistoren, fectively eliminated. divider then a voltage divider need not nreledacrosstherectifierfilament to A third, and perhaps somewhatleft- he included in this powerpack.Or if further aid in hunt reduction. handed advantage of this systemis that the receiver is one which requiresonly makes use. The filter circuit employed two platevoltages, then only two taps ofthe choke input method.This ar- advan- 68- 13+20 8+100 B-1180 ricer.'be provided on the power pack rangement hasseveraldistinct H H 1010311 70 1805. ID 250V. tagesover thecapacity inputtype of * 4. BLACK TWISTED voltage divider and only two by-pass con- filter.Most important is the better volt- densers will he needed. age regulationobtained.Thisisespe- pack is cially important in short-wave receivers The construction of this power which employ anr.f.stage and control simple.The power transformer has all the sensitivity by varyingthe cathode or terminals brought out the bottom in the grid bias.Such control varies the plate forts of color coded leads.A large cut- eurrenT of the r.f. tube and as aresult, the chassis is not required to ac- unless good power supply regulation is out in obtained, the plate voltage applied to the commodate these leads as they can be other tubes will vary.This is one tea- readily passed through two % inch holes. -onwhy in such receivers reducing the Suitableholeswillberequiredfor sensitivity of the r.f. stage may cause the and detector to spill over into an oscillating anointing the two condenser cans state. onefor the 4 -prong tube socket; all on nother advantage of the choke input are top of the chassis.A similar hole filter is that the likelihood of one or the BOTTOM SOCKETFOR -80 should be cut for the cable plug socket filter condensers "going west" is greatly VIEW RECTIFIER TUBE in one side wall and smaller holes for diminished. The surges which cause condensers to break down are much less Fig.I the a.c. cord, in one end, and fstr..the. off- 1935 SHORT WAVE MANUAL

on switch in the side wall opposite the screws of the input choke, CHI. thevoltagerequiredislessthanth:- cable plug.The location for mounting This power pack shouldprove highly normal output-ifthepower packitis the various parts inthe is made clear satisfactoryfor useasaB supply unit obtained front the toptap of the divider, illustrations.The wiring is also clearly foranyshort-wave receiver whichre- adjusting this tap to the exact value de- showninthepicture wiringdiagram, quires 90 volts or noireon the plates.If sired. Ifthe receiver has heatertype 6 - Figure1. The color coded wiresare volt tubes their filament supplycan he markedOn ibis diagram for the sake of taken from thepower pack also, after clarity.The center -tapped resistor RI is first beingsure that the filament wiring mounted directlyonthefilamentter- in the receiver is not connectedto any minals of the rectifier socket and the of the other wiring.Also,itwill prob- voltage divider is supported byits con- ably be found desirableto rewirethe necting wires, the low end being securely filaments with twisted pairifthefila- solderedtoalug under thenearest ment wiring was not originallyof this mounting screw of the cable plug socket. type. This lug is also 1'001041411 tothe B-tee- Theplate.supply minal of this socket, grounding ibis voltageobtained ter- from thispower pack is almost absolutely minal. The centertapsofthehigh- . free front hunt.In tests made witha 3 - voltage secondary and the. 6 -volt filament r tubet.r.f.regenerative receiver not the. winding of the transformerare grounded 11 H 8+20 8+10010180o- T0 100Y. 10 1800. 70 2500. slightest traceof hunt could be heard. tothe.chassisatoneof the mounting even when operating at 20 megacycles. Fig. 2

land Isolantite coil socketare mounted on 1/2 inch bushings to facilitate wiring The their connectbms, which are locatedun- derneath. The coils employ.'are the standard Gainer Hammarlund plug-in coils of the 4-prott;t type.These were foundtorontriloite MITE model. of the "Gainer" shown here materially to the effectiveness of this re- 1 isan adaptation of the originalre- ceiver duringthetest,.Due totheir ceiver developed by the technicalstaff design, the "ham" bands fall toward the of "Radio" and described inthatmaga- high -frequency end of each coilrange, as zine.The detectorisone of the new do also the popular short-wave broadcast 6D6 tubes and isthe equivalent of the bands.As aresult ofthisa favorable -57 emrept that itis intended foropera- I./C ratio is obtained with correspond- tion from a 6 -volt battery or transformer. ingly high efficiency for theseranges. The type -76 tube employed in the audio stage is the 6 -volt equivalent of the -56. Either a storage. batteryor a 6 -volta.c. filament supply only he used.For the ',Lit of Prat., plate supplyt ither a B eliminator or B II )1,1A It LUND rnotit.crs batteriesmay be used.The voltage!nay GI-Midgetvariablecondenser,type 1111:- beup to 200, although 135 volts will give 20S (.2-Midgetvariablecondenser,type MC - good results. 110M (land -spreading tuning is provided, the C3-Equalizer rondenser, type EC -35 L2-Four-prom pltta-intollset.type 140 tumid. condenser, C2, servingas the S WK-t coarse tuning or I...id-setting, condenser. choke, type 01-X while the critical tuning is accomplished 1 lsolantite 4 -prong, sorbet, type S-4(fel with the 20 .nnnfd. condenser, CI,which coil) is controlled by the main tuning dial. MISCLUANEllt.'S C4--Aerovoxtype1400micacondenser, The circuitas shown in Figure 1 em .00025 mfd. ploys the conventionalmeans for obtain C5-ierovoxtype1100miencondenser, 'lig regeneration in the platecircuit, con- .01 mid, trolled by varying thescreen -grid volt- CAr-CornellDiabilierbY-11101.1condenser, age of the 61)6 detector for whichpur- n atl.. 200 volts 1:7-CornellIhtbilier by -pa.:: condenser,.5 pose the- potentiometer 112 is employe(l. mfd., 200 volts The single audio stage is coupledto the U.11.-Xerovez pigtail mica condenser, .0001, detector circuit bymeans of a eombina- mid. C.11-ThwilarKOR 200 henryaudiochoke, Lion of impedance and resistance. type T2927 The terminal strips and the Hamm.-- 111-1.R.C. metallized resistor, 1 to 5 mozehms R2-1-treleypotentiometer,type VAOMP, 50,000 ohms 113--Afaxleypotentiometer.type1`500111P, 500.000 ohms 11-1--I.R.C. metalized resistor, 10,000 ohms, 2 watts Eby0s-trnr:::r11strrbeC.:,:;:ke';.""isoV;nti7:: socket Eb'llt(;;;=.r7tinitrb"C(71::-ks';-(:"Isoilf:ntit.; socket Eby5 -gang terminalstrip(screwlet- minaN ) Eby2 -gang terminal-artptserewter- minals) Eby 2.. ngler ' alstrip( tip jackter- minals) Karr.-littsch vernier dial (large) '1Ougle snitch,fi .11 .St 1.111mintintpanel,12 inches by 7inches (cutanddrilled-MantheItmli Man) 1011A, inehes long, 91/, inches Fig. 2 Fig. 1 tie, 12 The HAMMARL UND

The RadioAmateur's Handbook 3-Tube Band Spread A C Set

SOONER or. Inter most own- ersof regenerative receivers feel the urge to try the use of List of Parts radiofrequencyamplification HAMM ARLI-ND PRODUCTS ahead of the regenerativede- tector.In the days when only Li,l"2-Midgetvariable condense,type triode tubes were available the MC -20-S complications in this were se- C3, C4-Midget variable condensers,typo and at best very little am- MC14O-M vere LI, L2-Kit of 4 -prong plug-in coils.type plification was obtained in the SWK.4 r.f. stage. With the introduction L3, L4, L5-Kit of 6 -prong coil-, and popularizationofscreen - typo MM.() gridtubes andr.f.pentodes, RFC -11.F. choke, type CII.X Isolardite socket, 4.prong, type 5.4 however, the picture has The single audio stageis impedance 1 isolantite socket, 6 -prong, type S-6 changedcompletelywiththe coupled to the detector circuit.It em- 'tube shields, type TS.50 result that a well designed r.f. stageadds ploys a type -56 tube which is also self Flexible couplings, typo FC tremendously to the sensitivity and gen- biased. MISCELLANTX/US eral behavior of the regenerative reciever. Itisimportant that means for con- The receiver illustrated here represents trolling the gain of the ri. stage be pro- Ca, Cf., CR-Cornell Dubilier .01 lad., 200.. agood example of such a set.Itisa C7-Cornell Dobilier .1mfd., 400, vided on the front panel of such a re- C9,C10-CornellDubiliertype11C-227 model constructed after the description ceiver asthis.Otherwise even moder- 1.0 mfd., 160 v. which appeared in "The Radio Amateur's will the C11, C12Cornel Dubiller .00025 mfd. atelystrongsignals overload CH-Thordarson audio choke, type T-2927 Handbook," tenth edition. detector. Iftheregenerationcontrol R1-.I.R.C. resistor,5 megohaus In the construction of this model there alone were depended upon for this pur- R2-I.R.C. resistor, 210 ohms, 1 watt was some variationfrom the original, R3-Electrad potentiometer, 10,000 ohms posetheresults would be highly un- resistor, 50,000 ohm, 1 watt mainly inthe method of obtaining re- satisfactory because inaddition tode- 115-Electrad wire wound resistor,15,000 generation. The original had the tickler tector overloading, there would be a dis- ohms, 5 watts plug- R6--Electrtadwirewoundresistor,5000 in the cathode circuit and standard tinct loss of selectivity when regenera- ohms, 5 watts in coils arc not well suited to this ar- tion is retarded to reduce the volume. 117-I.R.C. resistor, 100,000 ohms, watt rangement.In the model described here, On the other hand, by controlling the Its-I.R.C. resistor, 5 megohnis % watt therefore, the circuit was changed to in- R9-I.R.C. resistor, 2000 oho, I watt gain of the r.f.stage, the input to the R10-Yasley potentiometer, 50,000 ohms clude the tickler in the plate circuit. No detector can be held down to a low level, I National illuminated drum dial, typo It change was made in the method of con- fullregenerationemployedandthus 2 Eby laminated wafer sockets, 6 -prong trolling regeneration-a potentiometer to 1 Eby laminated wafer socket, 5 -prong maximum selectivity obtained. 1 Eby strip,5 -gang (screw terminals) vary the voltage applied to the screen The band -spread system employed pro- 1 Eby strip,3 -gang (screw terminals) grid. vides continuousband -spreading by 1 Eby strip, 2 -gang (tip jack terminals) means a 1 Aluminum chassis and 2 aluminum shield Referring to the schematic circuit of of small condensershunted cans (see text), drilled and shaped -- Figure 2, it will be seen that the r.f. stage across the tank tuning condenser of each. Man the Radio Mara s quite conventional in every respect.It stage.These tank condensers arecon- metalized type. uses a -58 r.f. pentode, self biased. trolled by individual knobs.These may

BOTTOM VIEW TOP VIEW TO COIL DIAL SOCKET N9.4 LIGHT MIR

_ ., ...11 ..w C3xi - ai. i , .. TO TOP 11 1 a iliflajail! TERMINALA1 0 I IN, em OF VI. StLI! ',to CI3 .0 - iii, ''N ..- / ° °02i ',0' t-0-4--, , a. .-EY woo -0 1.1 ....._. ..., oo--a. e .. W ., COIL co ®o0© SOCKET/ , e .. rr \ VI, COIL Vi -58 SOCKET N2.2 -58 8-' 134.;'2.5V., V3 TO DIAL LIGHT 200m A.C. -56

Fig. 1 1935 SHORT WAVE MANUAL 13

beseen asthe two top control knobs in be interaction between the two circuits 11140132. of one will one ofthe accompanying photographs. 2 to the extent that the tutting The small hand -spread condensers, how- 1. ';'1CI C3 -.'3 4 M re . ea', react on the other and regeneration will LS 'A 13 ever, are gangedfor control by the single eI ry. be difficult to control. main tuning control at the left end of the -2. 'tP iz, '5 This receiver is intended for operation fromana.c. powersupply unit which receiver. i C2 C4 PR will supply approximately 200 volts d.e. Not only does thissystem provide a ,..r C3 CR CI 44 1.. -" fortheplates and21/2 voltsforthe very helpful degree of band spreading at TC6 1 heaters.Should it be desired to employ throughout the range any and all points 13 batteries, the voltage divider consist- of the receiver, but it also provides singly 0+.446.1 ingof R5 and R6 may be eliminated dial control within any hand which has RIO tr. and the "high" end of the potentiometer been selected by means of the tank con- R3 R5 R6 brought out to the 45 -volt tap on the B densers.Thus when the broadcast list- Of battery. ener has tuned the tanks to resonance in ;-. le. The chassis is made from a sheet of 16- the 25 -meter broadcast band, for instance, Fig. 2 gauge aluminum, 17 inches by 11 inches. he proceeds to tune in the individual The edgesare bent down 2inches all stations in that band with the single main built for use with lIammarlund standard around, making the deck dimensions 13 control, much in the same manner as he plug-in coils and with the tuning capaci- inches by 7inches.The front panel is would tune in broadcast band stations on ties used, w111 cover the short-waverange 131/2 inches. long by 7 inches high.The a modern broadcast receiver.The cir- from 19 to wellover 200 meters, with ade- shield calls eachmeasure 7 inches long, cuits will be found to track fairly well quate overlap, using9 pairsofthese 4i- inches wide and 434filches high. throughout the full rotation of the band coils. Theyareassembledoncornerposts spread dial, although some readjustment The secret of usinga tunedr.f. stage whichare drilled andtapped so that the of ther.f,tank condenserwill bere-. successfully, ahead of1 regenerative de- sides and ends of the shieldsmay be quired. tector, lies in providing through shield- securely attached bymeans of machine The model receiver shown here was ing.If shielding is inadequate there will screws.

whichcan be used as an oscillatoror monitor, in adjusting thecoilstothe The Ray proper frequency range The oscillator transformer L3 -IA is not particularly criticalas to the number of Five -Meter Set turns required.The specificationsare shown in Figure 2.The choke coil, Li, Prins three -tube super -regenerativere, consistsof 25 or 30turns of No. 36 1 zeiverwasoriginally described in de- silk -covered wire, spacedto occupy3 tailintheDecember, 1933,issueof inches ona piece of1/2 -inch diameter "Radio News."It was designed by Garo bakeliteor hard rubber roil. W. Ray, chief operator of Station WICC, Bridgeport, Connecticut, and owner and Thecircuitdiagramisshownin operator of an amateur station where he Figure1. C8isthe tuning condenser has curriedonextensive experimental while the mica compression condenser, work in the 5 -meter band. This receiver C9, isastabilizing capacity whichin is the outgrowth of his experiments. effectalso functionsas a band setting condenser.After the coils Ll and L2 The receiver is constructedon an alu- have been approximately adjusted, the minum chassis and panel for the sake of final location of the bandcan be accu- the shielding they provide.These aid rately made bymeans of C9.Thean- in the elimination of hand capacity, anti tennaseriescondenser, C7, whilenot to further reduce this trouble, the varia- primarily a tuning condenser neverthe- ble condensers are mounted at therear less playstin important part in tuning. of the chassis with longinsulating shafts and flexible couplings. In assembling thereceiver, it should be noted that all of the variablecon- Coils Ll and L2 consist of6or 7 densersare above ground potential and turns each of bare round bus bar shaped List of Parts must therefore be thoroughly insulated on a pencil.After the receiver iscom- HAMMARLUND PRODUCTS from the chassis by mounting themon pleteda little experimentation willde- in.nlating pillars about 1 inch long. The termine whether 6 turnsor 7 turns are CT-Midget variable condenser,type MC. 205 coils Ll and L2are soldered directly to required for each. The spacing between CS-Midget variable condenser,type MC - the condensers thus keeping their leads turnsalsoplays an importantpart in 140M as short as possible. determining the frequency bandcovered C.9. --Adjustable condenser,IsulantiteInsu- anda considerable amount of variation lated, type MUGS -140 Inoperatingthereceiverarather may be obtained by spreading the turns. 3 lsolantite sockets, 5 -prong, type S-5 strong hissing sound will bevery much 2 Insulated flexible shaft couplings, type FC in evidence untila stationis tuned in. This adjustment will be facilitatedif one MISCELLANEOUS PARTS canobtaintheassistanceof afriend Asastationistunedinthehissing who hasa 5 -meter receiver in operation, Cl-Aerovox condenser, .002 mfd. sound will be greatly decreased,or will C11, C3, C5-Aerovex type 260 by-pass sea- disappearentirelyinreceivingstrong dormers, .1 mid. C4-Aerovax condenser, .005 mid. stations. C6-Aerovux condenser, .001 mid. J-Single circuit (open) 'phone Joel. L1, L2, LS, 1.4, L5-(See text) i800 T. OF N2.35 itl,112-I. R. C.memlixed 2000 ohms,1 .5.5A.,C,..WLEIswoeuND ry, watt resistor R3-I.R.C. metaliced 3-olegolun,1 -watt re- 44,/ THIN sister -FIBRE r R4-ElectradtypoR1-205potentiometer, 50,000 ohms 115-1.R.C. motalired 200,000 ohm, 1 watt SMALL HARD resistor ( ,,,js RUBBER T-Thordarson audio transformer,typo R- -"TUBING 260 1.2inch length,1/4inch diameter, bakelite rod (for extension shafts) SMALL 1 Grid clip jr -MACHINE 2 Type -37 tubes 14 SCREW &NUT 1 Type -Sit tube Aluminum for chassis and panel, 1/16 inch l""AAVit6ET46,Z" 1 5 -wire battery cable 1 Kure-Kasch vernier dial Fig. 1 Fig. 2 14 The HAMMARLUND The Doerle 2 Tube Receiver

MR. WALTER C. DOERLE is well-known for his vari- ousshort -mute receiver designs and the receiver describedhere has been justly popularwith short-wave enthusiasts. Basic- allyit isnot unusualinthe circuitemployed. However, careful consideration of design details has resulted in this par- ticularMerle receiverbeing plate circuit to ground, thusby-passing especially popular sinceitwas theprimaryoftheattdiofrequency. first described in the magazine transf or neer. "Radio?' A.type -30 tube isemployed for the Analysis of the schematic cir- the by-pass anynoise regenerative detector and another for cuit tliagram in Figure 2 shows thestand- pose.being partly to single audiostag-.Two PA volt dry ard tickler method of obtaining regenera- that may develop inthe potentiometer cells are used for the filament supply tion, .eel a capacity -coupled antennacir- The condenser C4 isthe normal plate rheostat which completingthe.r.f. and are controlled by a cuit.Band -spread tuning is provided by by-passcondenser is mounted back onthe chassis, asit meansofa smallvariable condenser, C2, requires only oceasiental adjustment. List of Ports shunted across the larger tuning capacity, Hanunarlund plug-incoilsof the 4 - Cl. HA NINA 111.1 Nnritontrurs prong, 2 -circuit type areused. The ,condenser Cl is used for tuning cl-Midgetvariable condenser,type MC - to the desiredrange, then thesmaller 14051 The chassis consists of a piece of16- condenser will spread the stations in this t :2-Midge tvariable condenser,type MC - gaugealuminum, 131/2 3.3S range over a wide area onthe main tun- :2,-Ett anti., condenser, typeEC.3.3 inches wide with the four corners cut ing dial.Inasmuch as the smaller eon - REC--12.F. choke, type CH -X OM and thefour sidesbent down to coils, type SWK, I 'Netof-prong plug-in form walls 2 ittelies high, leaving a deck denser is utilized fur all exact tuning, it 4.1proeg Isolantite socket typeS4 iscontrolled by the large dial inthe, space. 91/2 inches longby 7 inches deep. renter.The "rough tuning" condenser, MISCELLA NEOUS The front panel, alsoof16 -gauge alu- adjustment, and C3, CI-CornellID obi tierstiescondense, mit lllll 1,.is10 inches long by 7inches Cl, requires less critical .00025 lad. may therefore becontrolled by a small Cs-Cornell Dubilierpigtailby-passcon- high. knob, as shown at the lower right corner denser, .25 ntfd. It will be noted in Figure 1 andin of the front panel. Some builders prefer It I -1.n.c. resistor,1-5 tnegohms ter- i:2-Eleelrati,typeR.1.205potent toMC., the photograph that there arcfive to have the largecondenser controlled by 50,000 ohms minals shown onthebatteryterminal the maindialandto use thesmaller 113-Electrad, type R1-204, 10 ohmsrheo- strip.Only four of these are used anti condenser more in the nature of a trim- stat SW-Toggle switch,s.p.s.t. a 1 -gang stripwill therefore be satisfac- mer.Where this system is preferredit T-Thortla montype157:16a.f.trans- tory. is only necessary to transposethe posi- former Eiy -t-prong sockets, wafer type. orIlan, To tune, firstfind proper adjustment tions of the2 condensers on the panel. nmriond Code S-,1 Isolatitite sockets for the antenna condenser, C6, byad- the wiring of the receiver remainingthe Kurz-IVaseh vernier dial(large) vancing theregenerationcontroluntil t same as shown in thepicture wiring dia- I Aluminum Doerle panel and chassis the Radio Man) the circuit breaks into oscillation, then gram. Eby 2 -gangterottinalstrip(tip jackter- tuning throughout the range with con- Regenerationiscontrolled by means minals) to strip(screwter - denser Cl. Ifitcannot be stale ofthe potentiometer,I{2. A .25mfd. 1 Eby2 -gangterminal oscillate throughout this range, decrease by-pass condenser, C5, is connected across ter- 1 Eby4 -gangterminalstrip( screw the capacity of the condenser, C6, until thispotentiometertoground-its pur- minals I itis found possible to maintain oscilla- tion throughout the: entire tutting range. - 2 OR 3V. If, on the other hand, too much regen- B+45 TO SO V. B- erationisobtained,thenincreasethe PHONES.,, capacity of C6.

GND

ANT

&16® 'PHONES' 5 ,04 8+45 TO 9.0V. .S -T12,+ TOP VIEW 2.c.OR3v. BOTTOM VIEW

Fig. 1 Fig. 2 1935 SHORT WAVE MANUAL 15

design and the Pentaflex takes full ad- vantage of this.The overall size is only The Pentaflex 7 inches long, 5 incites high and 3 inches sleep. The ehassis is formed froma 7 IN spite of its tiny size, this receiver, inch by 5 inch sheet of 16-gauge alumi- whichwas originally described in the num bent down 1 inch all around. September, 1932, issue of "Short Wave This provides deck space of 3 Craft," provides real 2-tuhe results. inches by 5 invitesafterthechassishasbeen at - The method ofsmploying a pentagriel (achedto the hack of the 7 inch by converter tube such as the 6A7 toserve Melt panel b.,:means of 2 screws. as both a detector and an audio ampli The pIng-incoils employ.' arcthe tier stage is made clear in Figure1. Here standard Hummarlund 4-prong type, four thescreen -grid section of the tube is con of whichare employed to coverthe entire fleetedlike any otherscreen -gridtube short-nave range down to 19 metres. employedas a regenerative detector. G4 isthe control grid, G3 and G5 together constitutethescreen, and P the plate. ListofParts The triodesection, usedasthe audio Rear View HAMM tRI.LND Puourcrs amplifier, employs G1 as its grid and 1;2 Cl-Equalizer condenser, type EC -35 as its plate.The cathode K iscommon C2-Midgetvariablecondenser,typeMt'. to both sections. The resistance coupling between the sections consists ofRIas 110711 I.I.1,2-Standard set 4 -prong plug-in coils, the plate coupling resistor,C4 asthe 1,pe SWK.I coupling condenser and RIas the grid 1 1 -atomise coil sucker, iytie S-1, Prom, leak. The headphonesarc connected in M ISCELLANEOUS C3, C5-Cornell Debater by-pass con- densers, .1 tad. C4-Cornell Dubilier by-pass condenser, All C6-Acrorox pigtail mica condenser, .0001 C7-Aerorox 'Pigtail m condenser, .0005 mid. rnetalizedresistor.3 megohms. watt R2-1.R.C. metaliredresistor,.100ohms, tA watt II"-Electrad potentiometer, 50,000 ohms R5-I.RA:. metalized resistors, .25 megohms. watt Kurz-Km:eh vernier dial, small size 1 Grid clip I Toggle switch, ti.p.s.t. Eby 7 -prong wafer type who socket fur 6A7 tube. or Hamm:Aunt( Code 5.711 Panel View Isulantite socket 1 Pentaflexpanel andchassistCe,text (lit,,,, the Radio )tan) the circuit of G2 (the triode plate). I Eby 5 -gang strip(screwterminals) iously lends itselfto compact receiver Eby2 -goes...rift(serestterminals) IL Eby 2 -gang strip (tip jack terminals) Fig. 7 This application of the 6A7 tube ob-

deep.The front panel is of aluminum, A Dual 10 inches long by 7 inches high. On this panel are mounted the tuningcon- denser C2, the potentiometer RI (with Regenerative on-off switch SW operated bysame shaft) Receiver and regeneration control condenser C3. Hlti2 -tubereceiver, which was de- ListofPurls 1 ;crib.' indetail in the June, 1933, 11ANINIARLIINI) PRODUCTS issue of "Short Wave Craft," providesan unusually flexible system of regeneration CI-Equalizer condenser, type EC.35 C2-Midget variablecondenser,type MC - control Iry combining both the condenser 140 -M and potentiometer methods.Thus the C3-Midget variablecondenser,type screen -grid voltage can be adjustedto 1.1. 1.2Stanclard 4 -prong,typeSWK. I. thevaluethatprovides the smoothest rails regenerative action, then the condenser RFC --11.F. choke, type C11..X 1 Isiiiiintite rail srieket, .1. is employed for the variation requiredin Rear View prong, type 6.1 lining.Or this methodmay be reversed NIISCELLANEM s ifdesired, fixing the adjustmentofthe condenser and usingthe potentiometer I.C6 --Cornell Duhilier mica condensers. as the operating control .00025 mfd. The receiver is constructedon a wood 1:5-Cornell flubilier by-pass condenser,.1 ,ofd. baseboard 95,4inches long and 7inches C7-Cornell Dubilicr by-pass condenser. .01 'oft!. C11--.-Thortlarsowe audio choke, type T-2927 RI -1.11.C.metallizedresistor, .5 megohtes watt R2-Electradpotentiometer,typeR1-205, 50,000 riitiiis 113-1.1t.C. moralized type resistor, .5 megoium RI-Electrati 10 ohm rheostat, type RI -204 2 Eby moulded tube markets,one 4 -prong. one 5 -prong, or Illammorlund Code S-i and S -S Isolantite sockets 1 Eby2-5,irigstrip(screw terminal.) I thy Ssitiingstrip(scree terminals) 1 Eby 2 -gang strip (tip jack terminals) 1 Wood baseboard, Inches by 7 inches b, inch 1 Aluminum panel 7 inches by10 inches (Wan the Radio Man) 1 Kurz-Km:eh vernier dial, large size 1 Grid clip Fig. Panel View The HAMMARLUND 1.935 SHORT WAVEMANUAL The A. R. R. L."Ham" Receiver

THE receiver described here is one which is featured by theAmericanRadioRelay League and the magazine QST as anideal job for a budding - "ham".This receiver was de- scribed in detail in the A.R.R.L. booklet "How toBecomea Radio Amateur," 3rd edition. To quote from the descrip- tive article in this book: "The prefer to wind their own coilsand the receiving set we describe is of necessarydatais therefore given here. simple design and construction. based on the use of Hann -mu -landisolan- Itis easy and straight -forward tite coil forms. toassemble and operate, and Coil Data -yetwill readily bring in amateur signals from distant stations with a suitable an- List of Parts LI L2 L3 Frequency Range tenna and ground. ILAMMARIAINI) PRODUCTS No. 1 70 20 10 1000 to2200 kc. "Some of our readers may notice that CI-Midget variablecondenser,type MC - No. 2 30 JO 10 2250 to4200 kc. the circuit is similar to the old familiar 1208, 2 sections of 100 mead.and No. 3 11 7 5 4200 to9000 ke. `three -circuit' tuner so commonly built 20 mmfd. No. 4 5 5 5 9000 to 18000 kc. 1-2-Midget variable condenser,type MC - All coils are wound in the same direc- by broadcast listeners in the early days 140111 of broadcasting. Do not think, for thi4 1:4-Equaliser condenser, type EL -35 tion using No. 30 double silk-covered it wire, close wound.Approximately 1/16 reason, that is not a particularly good LI,1.2,I.3Standard 3 -current,6 -prong, amateur receiver.It may surprise you plug-in coil kit, type SWIC.6, orfour inch spacing is provided between coils. to know that this tuner, with occasional 6 -prong coil forms, typeCIE -6 In each case the grid coil (L1)is the modifications, is used in the majority of choke, type CII-X top winding,the tickler (L2)is in the 5-4 the amateur stationsinthiscountry. I 4 -prong Isolantite socket, type middle and the antenna coil (L3) at the 1 5 -prong Itolantite socket, typeS-5 'quell of the international amateur work, I 6 -prong Isolantito socket, type S-6(for bottom.The top end of the grid wind- expedition communication, etc.,is done coil) ing corresponds with the coil terminal with receivers using this circuit." MISCELLANEOUS marked No. 1 on the schematic diagram, While this little setwasdesigned pri- C3-kerovox type1460fixedcondense, the lower end to No. 6; the top end of .0001 mid. the tickler to No. 3, the lower end of marily for the reception of C.W. and Itl-Eleetrad type R1-204 rheostat,50 ohms 'phone signals from "ham" transmitters, R2-1.R.C. metallized resistor,2 megoluus the tickler to No. 2; the top end of the the very features which make it a good T-Thordarsou type R-260audiotrans- antenna coil to No. 4 and the bottom end "ham" receiver will make ita good re- former (tip jack terminals) of the antenna coil to No. 5.The num- ceiver forany type of short-wave work. I Eby 2 -gang strip bers marked on the coil socket in the I Eby 2 -gong strip (screwterminals) The tuning condenser really consists I Eby 5 -gang strip (screwterminals) picture wiring diagram, Figure 2, corre- 1 burr-Kasch vernierdial(entail) spond to the coil terminal numbers on of two condensers assembled inasingle 16- I 7 inch by 10 inchaluminum panel, frame. The 100 nimfd. section is used for guage (cut to sizeand drilled-Dian the schematic diagram, Figure 1, and the coarsetuningor bandsetting. The the Radio Man) ends of the three windings should connect smaller section provides I Wood baseboard, 91/2inches by 7 inches with the coil form prongs indicated by a capacity of 20 by 3% huh thick nunfd. and it is with this portion that the 1 'toggle switch, the numbers on the coil socket. finetuning and band spreadingisac- complished.Its shaft is brought through the front panel to the main tuningcon- it spreads the station out onthe dial so trol.The knob for adjusting the larger that instead of two orthree stations fall- sectionisatthe rear of the condenser, ing within one degree, asthey do on so behind the panel.The band spreading many receiverswhich do not include this permitted by thisarrangement is an in- feature, they are spread out over adial valuable featureof the receiver when range ofperhaps five or ten degreesand operated on the 20, 40,80 or 160 -meter thus tuning is much simplified. "ham" hands and isa decidedly useful Regeneration in the detector circuit is feature on otherranges as well because accomplishea by meansoftheusual tickler and is controlled by meansof the variable bypass condenser, C2. An aluminum front panel is used to minimize body capacity while tuning the receiver-This panel is screwed to the front edge of the wood baseboard.The three Hammarlund Isolantite sockets- this type of socket is recommended be- causeof their low r.f. losses-are elevated approximately Vs inch above the base- board by means of bushings which are supplied with them.Similar bushings provide a convenient means for mount- ing the 3 terminal strips. The receiver as described here pro- vides excellentresults when Hammon. lund standard 6 -prong plug-in coils are Fig. I used.However, some constructors may Fig. 2