Show 4 7 Arr ar mr 1 1 1 ad X 1100 av XA I 1 ile 1 40 A 1 owl 1 arfi diagram of the selective five tube receiver described in this article the apparatus indicated in do dotted ted line Is optional by FRANK W ARTH in the new york tork herald tribune there Is nothing particularly new tn in this circuit which la Is the old west kant cant with a lew few variations the set originally was designed for or local reception only but one weal local did not come in very well so BO a ptole c of radio frequency was added A location in the center of manhattan was wa selected for a test the met act Is fairly compact the panel being 7 hy by 21 inches and the baseboard rd 12 by 20 inches the chief claim of novelty la Is the placing of the R F secondary and regenerative colls coils on one form and having them till all of the same diameter that simplifies the lie work somewhat there tire are five tubes a II 11 F amell tier fler a detector and three audio amplifiers to tile the author selected belec ted the type of edlo au audio amplifier used bec because autie the transformer tives gives a strong initial input diee from distortion for the two ne bustance coupled stages binges to amplify the result 1 im a signal of surprising fidelity and somewhat greater volume than ii a two stage transformer coupled amp amplifier lIfler the colls coils are of the ribbed ape of hard rubber tubing recommended for its lt high electrical efficiency there are 12 ribs riba running lengthwise of thu the tube find and spaced equally abou arou around idd thee the circumference c the turns of wire I 1 touching only the tops of the ribs leave a space the colls coils and provide profile v practically an air core the antenna coll coil wits wound ns shown in alg 2 with no 22 P D 0 C wire 15 turns for the primary coll coil 11 TA II and 41 40 T I 1 04 N 14 0 N 4 14 1 ill IL 11 i constructional data on antenna and radio frequency coll coil of receiver turns for or the secondly secondary 12 the number of turns for this coll coil may vary depending upon the length and type of aerial used the serial aerial used mth fill this sit set was about 75 feet in ili lenith if a shorter berfal Is used use 50 to to rl ISI turns may be required the s iiii between the primary and see sec andary Is not critical from one eighth inch to one om quarter inch works construction of colla coils the roll coil form forin shown in the drawing awing Ir 1 I ing ig A 1 I performs a threefold duty dut that hint of supporting support ln the it 11 F primary the 11 F secondary and the the live coll coil tile the it II F primary coll coil to la com composed poRed of 20 turns turn of no 22 D 0 C tile it n F secondary econ dnn coll coil 14 of 46 turns of no 22 2 1 I r C C and the regenerative gen coll coil 1 15 I of 12 turns of no 10 30 1 I C a 0 the spacing ln he between teen the 11 F and the lie it IS F I 1 secondary must le he two inches or slightly more may mil even better the r nera the live colt col 15 Is about nl lit ne englith indi inch fi birin mil thi ze condary to ti obtain a c n lui pr er of oxe P capacity for the lie keiu prator a larger evri denser enn lie he aed by h re ri boving ing a number of if me IK rotor n tor plates in 11 tills case a 45 haq ns bed after removing four rotor pi tes ti which brought bro the capacity doun il n tu to apprel ma ninthly tely tudd th alio inductance forms van he be fas toned to tilt lii hae hi hoard with w th a vr cooil 0 MI or ele U 1 it adt inch or so io on D 8 shaped of brass ore mid end of the S Is then men wiled bolted to the form ud lie other end screwed to 0 o the be base board for 1 or hest best rei balts it good audio transformer should be used one ine of not too digh n ratio one of the modi rn larger transformers vu owald uld kle give ideal results result the resist lOance nice couplers cou should of course bi be of the highest grade to bllance blance bp lance the he audelo er A little pains taken to obtain the tight right resistance values Is iq really worth rt ille as the lie fullder will he be amply repaid by bv the results obtained only two vernier chaler dinn tire required n its the regenerative can all 1 ner iier la Is riot not critical three dials of the same borne design make a better looking panel the R P F tube may or may not require a negative bills bias depending of course on the characteristics of the particular tube from one and one half to three volts usually will make the tube function properly to include a C battery at this point remove the lead X XI as shown in fig 1 the set bet Is easy to tune as there are only two major controls antenna dial and wavelength wave vave length dial after the detector tube la Is properly adjusted the setting of the rhe rheostat can remain permanent and the volume of the output signal controlled entirely by the it II P F tube rheostat it if the colls coils are properly balanced the dials should read alike and then can be successfully logged when tuning the set the dials should be rotated slyly a degree at a time al ag the stations simply drift in and out without the usual whine or whistle if the regenerative unit la is correct over regeneration Is indicated by signal becoming mushy when too much capacity Is used that la Is when the dial Is advanced too far it if the set hai a tendency to plop remove two or moro more turns from the secondary side of the regenerative coll coil as a menna means of correcting the fault another method to Is to nune move the regenerative coll coil from onti one quarter arter inch to three eighths inch away from the secondary coll coil tile the value of the C battery used in the audio circuit may be anything from four and a half volts to nine volts or more if ninety or more wits volts of ill it battery are used most audio amplifiers work better with a 0 battery slid and the saving of B battery Is considerable in the long run wavelength wave length range the set should ordinarily tuno tune from to matei g smoothly and with equal volume however the author found one set in several he built that was for some reason or other a little tricky on wave lengths under meters that Is 19 it lind had a tendency to spill over and was difficult to balance this thir tendency was corrected by malting making use of the rice system of neutralization iza tion tills this consists of an inductance and a neutralizing condenser these parts are indicated in the drawing to show allow their location but need only he be used if difficulty Is experienced on the low wave lengths there Is however only one chance in a hundred of their being required the coll coil Is composed of the same number of turns its as the 11 P F coll coil and Is wound direct directly y e over ver the R F coll coil the tube in the last stage can be a A it if the horn type of loud speaker sp ealer Is used however if the builder intends to use a cone type speaker he will require a greater output voltage properly to vibrate the cone the use of 0 f fk a power Is ug here as a sul suitable table means of providing the essary power without distorting the signal an am or similar file men ment t control device cofone of one half ampere capacity must be provided for tills this type of tube the atie choke and large condenser shown in the diagram can be used or not no tits as te builder sees it with their use tile the output signal will be much smoother as the heavy direct current I 1 la 8 bypassed by h passed through the choke ina in stend stead of being allowed to pass through the speaker coll coil parts required the following Is a list of parts actually usell but there la is no reason I 1 w why hy the set would not work well it 11 other equally suitable parts pit arts of good quality were substituted one cabinet 21 inches long and 12 inches deep one baseboard aby 7 by 2 20 inch wood brass strip by 1111 1 11 see text one panel 7 by 1 3 11 10 inches two varla arl le de condensers gen cen oral instrument oie one variable condenser oen eral instrument five A tubes two rheo rheostats oats trio tito sockets three sockets gang bakelite two tubular forms 3 by 6 inches and I 1 by 3 inches badlon hard rubber one grid leak variable one grid condenser OW 5 three and mountings I 1 A V one audio transformer two desisto couplers four rI stances 05 03 25 1 and 20 two coupling condensers twelve binding posts terminal strip 14 1 by 4 by sl 81 S l inches I 1 terminal strip 1 by 8 by 3 lf inches thre dials one filament twitch switch one pound no NB 22 D C C one eighth pound no 30 D CL C necessary screws wire for conner tlona etc |