25 M y to a 3 IK tro 20 A p 7 1 11 a 10 B 8 t 1 I 1 01 01 0 1 i fa 0 26 Q 4 aj 60 0 CJ IM W 10 ac 0 iiii vom oil copyright FIG 2 broadcast 1 how to calculate tube constants plate impedance Is ascertained with wl a simple apparatus that it li 19 l i not tile lie illiam 9 of ill ohp average radio fill to t tile the konstants ton stants of ills his own onvil tubes tabes Is it amply tinned proved by b the on oil tills by keith laboratory expert in ili tile the Spec special lill slaw sliced 4 number of llanillo broadcast maragne maR alne I 1 the only apparatus necessary Ic besides sIdes tile the I 1 tube socket rheostat bat batteries unil anti perhaps a potentiometer to coil arol grill grid bins bills consists of two a i double runge range voltmeter find it meter the former should have lifave ranges of fro from 0 to 10 and not 0 to volts wilile tile the should read ul up to I 1 10 ralls mils and ill us its higher readings inny any be require of it a shunt will lie ile nee necessary emary the alip object of it 11 shunt is 18 to diablo able herlier readings than the ligure on oil tho the dial fact face to be rend read in ill his broadcast article I 1 clr explains liow low the lie factor plate impedance mutual conductance duc tance and d c and a c be found here it Is intended briefly to outline ills method of arriving nt fit tile the plate impedance it Is desired to obtain the lie aboe of a A tube tittle wr we first of nil set up tit our nur apparatus its as shown in the accompany in fig 1 here it a voltmeter Is clion connected across enell of the three feets of batteries but of coi co itse lirse our one duble double ill meter t e r 1 Is 4 all th that t I 1 Is it bestiary est nry iary for only one read leading ilig Is taken tit at it tint time the grill battery should prof drably consist of it battery or several scelah 11 1 volt alt batteries so that 2 volt olt or nr 1 volt olt variations are possible A potentiometer Is 19 not shown in ili the bilm diagram but one allf rally may lie ile us used ed to to nd lid vantage for varying the grill grid blas bla how to proceed alie r ile setup set up complete we ve place our voltmeter across lilt ho filament posts of the socket and adjust the rheostat until the meter rends reada 5 wits volts lor for our first curve that shown ns as ega on tile cahnt we omit the grill grid buttery battery lg eg represents grill grid blas bias having obtained a pipe piece of graph paper and marked it ort oft similarly to the chart shown herewith we tire are rendy really to proceed we adjust the 1111 1 11 battery voltage in ili SS 22 volt steps and read the plate current for each step thus we are able to plot a curve such its as that one marked 1 kgb go 0 on tile the nc ile companying company compa nying ing cliart chart to get the plate iniard we nie tit at 7 aro ro volts grill grid bing bias then we rutih p the following formula in which lip represents the plate impedance change in plate voltage Cli chapka alige in ili plate current referring to our chart we rend read that walli it zero bins bing it plate olane olt ne e of volts ats gives ull u a 13 plate current anil tint a isvolt I volt plate ultina ul tisa gives us 3 plate current we put lint down don milt hat thus alius 1111 tt voltage plate current curant 13 48 8 3 TS volts 10 mils Is g 0 we vc use volts klinis find niu all peros in our formula libbe abid so MC convert our 10 to inuss ps und and bill in tile lie formula 78 alp ilp ellms therefore tile lie plate pinto impedance at it zero volts grid his bills li 14 ollins far ther curves may inny be drawn to to ortall tile tip paiit impedance nt at various iii rlou grill blaseg anti these tire flown in fig 2 as aa iga ng IB 4 IK 8 lind ug IK lo 10 tandem tuning condensers Conden sera tandem tuning of condee condensers ers to tit decrease the lie number of separate controls lins has become quite common there fire some sun tinel idill facts concern ing tandem tuning which must ile ho considered cou livered it if attl efti tory results fire to lie obtained nod and these tl ie arc fir inter estl angly outlined la in n short article in the broadcast magazine the output and nd input 0 o lined eircil witult arru mitat le be exactly in ili betich st be tore the condensers may inay be t ss fully banged ganged tit in 11 circuit eircil t with two W J as 0 of tuned a ed radio ire quelley it is not lot a ellit cult mutter matter to gang g ing tile condensers fonden sers across the lie secondary condary he oils of the trims formers tit in the grill grid circuit of tile lie second radio frequency fre it bixl no I 1 detector let I 1 e C t 0 r the colle are it would not tap t vos possible sible however lio weer to control tile lie condenser tuning tin the grit grill cli circuit cult of tile ill first st radio freI limley alibe ly by tile lie scinie kill keidl which cOli controls the lie other two con condeles dells ers era even though the colls anti and condensers tit in tills ills circuit were matched with till the others tit the reason for tills Is simple le while tile the circuits controlled by tile the second mid and third condensers by virtue latue of the filet that they aliey fire both fed fron from tile the plate of if preceding tulle tube tile circuit tuned by the fir first st conderi condenser er Is being energized by the antenna an and ground system fit and Is therefore unlike tile lie others in charack rustles in ill the lilt radio broadcast article it a Is which makes possible the longing candeni tan deni tal tuning lill of tile three circuits fly by me file ins ans of the lie addition of an ain extra emril till tube alie ahead of re its grill grid circuit living title to the output of tile the now tulle lube Is connected the alie forner input of I 1 lie previous first r f stage singe thus thin tile input of tile the two r t f st stages ages and tile detector circuit art anro all connect connected ei to tile plate circuit of a preceding tube fa FIG G I 1 0 0 MX 0 4 volt A 0 volts V V lah hll C B copyright badh broadcast 1926 diagram showing how to set up the apparatus and providing all colls coil i ers are arc alii illey may in he tuned by one three gang it would he 10 possible to to gling tile three condenser s tile butic but tills would billil nin lre accurate ditc itc cutt liiK of f ill alie coudell er so FO ns its to tot for tiny in affect act of ahe vIr circuit cult tills la Is it difficult joh job ll it Is preferable to elther retain two tuo controls or to to ilse tin extra tube dnny io billil il lil blnche gi e control nrc art t il some compensating vvhs b lier aits eanet falling or ench circuit to resonance in bmw aps ll ps tills itrice It lev vice ice consists of 11 condo condi nir ner n ir connected in ili parallel olle of ahe alln ats j ilip stationary plates of if one ollo of ill lie ron dears dpn sers are mounted on oil a ll phot lt so as to penult allore accurate tuning hut hat no receiver that lias has birli tin nn adjust sible texture fesi turc can lie lf called a ilni le control set