Show 3 p ANT P d toll OIL COIL A A 05 A 4 5 V five tube tuned radio frequency receiver using low loss LOBB doughnut colls coils fly dy CARLTON E BUTLER associate Aeno clate member institute of radio Engl engineer neer s and american of 0 electrice ung steers the tuned radio frequency type of receiving set met employing two stages of tuned radio frequency detector and two stages of low ratio dudlo fro fre amplification la Is going to tic ho fur far find awny away the ho most popular broadcasting receiver for the coming season this Is due largely to the fact that the development of the horold coll coil for both radio frequency transformers and couplers has now re reo Relied ched the a id d danced stage where practically all of the bit bad features fei iturea of the tuned radio frequency receiver are eliminated with their use Vor olds lire are not new nev some of tile best engineering talent in tile united states find europe has been working on them ahcin for three or four years there to lie be some fault that hut could not be overcome that prevented their successful application in radio ro re cel calvers vers generally this consisted of lilyh losses in the coll coil itself that nullified the lie good effects gained by the peculiar shape of winding vinding this difficulty has now been overcome in the new low loss doughnut coll coil designed by frank one of the pioneers in the radio engineering field by the use of stagger winding I 1 shows lowest loss lose the stagger wound doughnut coll coil not only has the advantage nd vantage of tin an enclosed magnetic field which prevents but it also shows the lowest loss losa of any coll coil now on the market the enclosed beld field practically eliminates c the pickup of stray btroy big nals mils and static by the set sel these e factors combined mean the construction st of a radio frequency set with doughnut colla coils will produce ft a receiver unit that possesses tremendous volume amazing selectivity and n much better tone qui quality tilty than Is usually silly obtained bained with a set of tills this type until the introduction of tile the horold coll coil into the construction of tuned radio frequency receivers most nil all of tile the sets were built niong the sanie same lines with great stress nid laid on oil the nol nd vantage of different methods of ing receiver stable in operant operation I 1 on by preventing oscillation sonic some circuits used a n small balancing condenser between the grid of one tube and the plate pinto pt of the preceding tube others used a potentiometer or balancing resistance si stance of some sort in the plate circuit of tile lie frequency tubes without stabilizing condensers condon sera or of some sort the five tube set of this type lef la practically useless cringing in distortion and whistles when tit the receiver Is tuned timed to the wave length of a station tile the sole function of the auxiliary apparatus ta Is to add losses or resistance to the circuit to bring the total amount of energy town down below the oscillating point of the rT receiver eiver if tile lie samo panic circuit could be so arranged arrange range that the fields coins of the alie colls coils could he be balanced an and located in a 0 manner that no ho inter inciting of the magnetic fields of tile the colls coils would take place the volume and range of the lie re celver would increase wonderfully the tone quality would also improve with tile the absence of the auxiliary apparatus pa ratus tills Is exactly what Is lone done in the receiver described in tills article through the use of lew loss doughnut colls coils which have sett con tattled tallied helila and so prevent interaction inter action of the colls coils and circuits it Is for tills reason that it lb Is sary bry to mount tilt the colls coils tit nt critical il ingles to nold avoid whistling asid howling in practice the colla coils may be placa side by b side without any noticeable effects 11 As the magnetic field Is entirely closed no pickup effect Is noticed without the berfal find ground find and no static cc signals will be received ox ex capt on the exact wave to which the receiving merlill Is tuned this fills makes it nn an ideal summer radio receiver and it can be used near a powerful broadcasting station without interfere ence parts parta needed to billil l tile the re receiver celver you ou will 11 need the following parts I 1 antenna coupler low loss doughnut coll 2 low loss doughnut radio frequency transformers 8 3 frequency low loss variable condensers of cd ca lacity 2 3 to tc I 1 ratio audio frequency transformers 3 5 standard tube sockets with five 2 lf the 0 type of tube Is to be used this bombl nathon Is recommended operation coil can bo be by using a 25 ohm to control the tw radio frequency tubes and it G ohio rheostat for tile tho detector and two audio tubes 1 each tile the following capacity fixed mien condensers mad 00 06 niad and mad 1 2 or 3 grid lenk leak I 1 single circuit phone jack binding posts wire find screws com coin the list of apparatus needed the total cost of the receiver will approximate 10 40 tile the ree receiver can easily be assembled on it a inch panel without crowding but tile the conventional 24 or oi 20 inch panel may be used it if de desired |