Show ti s akk A picture diagram or of receiver which will bo be of assistance to novices who desire to construct voluminous DX set by HERMAN BERNARD associate institute of radio ludlo engineers once upon a time one saw variably variable condensers that had about 43 plate platea and were rated at mad capacity do you remember the days that value of capacity was waa extremely popular but butas as receiver celver re design improved and a higher ratio of inductance to capacity capre ity was thought advisable such values as an and particularly ined came into favor now the and tile the mad condensers are the most kopmar and as they fall in nicely with stil lemes of space conservation they well deserve their hour but the niad tuning condenser haa its use it to Is in the antenna circuit there are several ways of including it but tile one shown in the diagram Is as good as any the aerial in tuned the condenser Is used to tune the aerial tir cult tho reason for tho the abnormal capacity Is in that it Is perfectly normal in the position where it Is incorporated it Is in the aerial circuit and the antenna system capacity la Is across it to be sure the coll coil L would seem to be short circuit ing that antenna capacity but bui that Is not quite the tise case the inductances L and ll LI are in the he antenna ground system and he serial aerial ground capacity plays its important part in that lead this joint contribution constituting the reactance of the he circuit A mad condenser might be used instead of inai if one on were sure of what ones olles aerial capacity was but the gives a wider margin of safety ity the object of the large capacity tuning condenser is s to insure a dent clent ratio between maximum and an d minimum capacity so that the entire broadcast band will be tuned in the cIr circuit cult Is inherently simple any one familiar with radio rad locan can construct it modifying the grid return if feces eary A comfortable panel for tills this set would vou ld be 7 by 14 inches and it would be so laid out that the aerial tuning condenser Is at left the secondary tuning condenser at right and the three circuit tuning coll coil in center between the three circuit coll coil anti cl 01 would be the rheostat rl the jack ls Is placed at the opposite point the tickler would not require a dial A small knob would suffice surnce or a two inch dial while four inch vernier dials should bo be used on the two condensers A baseboard if used would be 8 by 13 inches secured to the panel bottoni bottom by wood screws the coll coil L would ho he placed horizontally 3 inches the end pate ate of 01 while the 3 clr cult coil would be mounted perpendicularly on the panel A socket shelf 2 by 18 inches would be busl as suitable aul table t coil cell data LU infix may be a n commercial 3 circuit atty ping lining coll coil the capacity of 02 2 depending on the coll coil us used ed most often this would be mad for those desiring to wind their own 8 circuit coll call a 8 thelt inch diameter stator stater form 4 inches high may be employed the primary lf consisting of 10 turns leave ae inc inch h space then wind 45 turns for the secondary 12 the tickler Is wound on a 2 inch diameter 2 inches filah and consists of 22 turns the wire la Is no 24 double cotton covered it Is often more convenient to use smaller wire on the tickler say no 20 falt for it matter there on the resistance score As it a shaft must penetrate the stator and be secured to the rotor part of the rotor winding will be separated at least the width of this shaft and finer wire makis makes it ft easier to put on enough turns to get regeneration on the highest receivable cei vable e wave the secondary la Is to be tuned with alm mad for use 65 55 turns for use 33 As for the coll L that will require some aliue experimenting experiment in g my bly own aerial has a capacity of 7 and the proper coil in 16 conjunction with a can denser for cl happened to be one comprising 81 31 turns on oil a 3 in inch diameter tuning no 24 wire being used but some antenna systems will require a greater number of turns sonic some a lesser number it Is a rood good plan to put on od 40 turns then peel em off as necessity dictates the set operates on a any ny of the popular types type of tubes including dry cell tubes mount tha th condenser cl on the panel also the condenser condense r ca then the n mount tile coil in tile center cater and next pui pat on the rheostat and jack put the th t baseboard against again st the p innel b ottom bottom mid pro provisionally Pinc ethe alie ull L and tile socket rocket the wl toll A ap I 1 mt w denser the docket at right the aerial post will be at left rear tile the ground post at rear center A battery cable avoids the necessity of binding posts wiring directions connect the A battery wiring on the baseboard parts first join A battery plus to the ap V plus post of tho socket and to the rotary plates platea ol of ca connect A minus to one side aide of tile the rheostat III the other side aide of rl to the F minus post of the the 09 00 type tubes have their filament grid and plate posts differently positioned from the standard base tubes so BO see that you correctly read the post designation on the socket after mounting L connect aerial to one of Ls terminals and to the stator stater of cl while the rotor of cl and tho the remaining terminal of L go to the beginning of the primary LI 11 the end of which goes to ground the end of the secondary goes to the lend that was connected to tho the rotary plates of ca the A plus lead while tile the other terminal of 12 goes to one side of the grid condenser ca the other terminal of qa la Is connected to the grid post of the socket marked 0 on the socket across the grid condenser which has mounting or clips for the purpose Is placed the grid leak normally 2 meg although tho the 09 00 type tube will stand a higher value of resistance say 5 meg the plate post of the socket marked P goes to one terminal of 13 the other terminal of which Is connected to the hooked spring of the jack it will be noted that in the picture diagram and in the text the grid return Is designated as A plus and this Is correct for nearly fill all tubes although in some few tn instances tile the grid return to A minus will work better the correct return to Is Import important ailt I 1 I 1 the parts parta needed i I 1 impedance coll coil L 1 8 3 circuit tuning coll coil 1 madl variable condenser cl 1 mad variable condenser ca 1 mad grid condenser with clips ca 1 mad fixed condenser ca I 1 single circuit jack I 1 1 20 ohm rheostat rl III 1 5 meg grid leak RZ 1 09 socket 1 7 by 4 inch panel 2 4 inch vernier dials 1 2 inch dial or knob I 1 blead B 5 lead battery cable Aces accessories one 4 volt A battery usual 1 C battery serving the purpose 1 99 type tube I 1 cabinet to match panel ano an baseboard sizes feet aerial wire 60 50 feet no 14 insulated leadin lead in wire 2 aerial insulators gu sula tors I 1 ground clamp note the use of a 99 90 tube Is presupposed it if other type of tube Is used make necessary substitution of equipment |