| Show POSITION AND SIZE OF GRID IMPORTANT I 1 determine value of negative potential necessary to reduce the plate current to zero in using i a three electrode vacuum tube in a radio set it Is preferable to maintain the grid negative with respect to tile moment in order to require the minimum of ener in the control of the plate circuit the relative position of the arld with respect to the filament and the plate and the size of the mesh of tit alif grid determine the value of I 1 D K H la Is the lie negative potential which must be applied to the grid lit in order to reduce the plato plate current to zero the little of F which Is the positive gild poten flat that will cause tile maximum or saturation cum nt tn in low flow lit in the lie platt circuit Is also determined by bi tile lelu thu live position or of the grid with respect to the Il lament unit and chite it if UK the greil Is of very ery fine binesh flit alie value of il 1 1 la Is small because the electrons in passing through the small mesh u of alie tit grid galil oil in their journey jounior from froin the lie illa inetie to the plate will negatively charge the grid gild and will be repelled similarly ft a small cliart nil all plied piled to lo it ii tine fine will tend to uc ae ce lerate the velocity velo of the electrons in case of a very ery charme anesh grid the electrons can pass through tin the nil ap lit in the grid without anning lit in so dona to tile lie charge till on it aud it relatively high potential viii ht lif re quiren on the grid to control tile electron stream or lit in other words I 1 the itie current curien flowing lit in the lie plute plate circuit t Uc Ite ferring tu to fig VIII OG O 0 G ts Is the lie current that will flow lit in the plate circuit when there Is no poten tini nil piled to the grid gild suppose a positive potential us as 01 0 1 Is applied to the lie grid the corresponding plate circuit current will be ID I D or ild il 11 1 D mote more than it wai as alien lien the grid had no potential applied to it A negative potential of 0 11 vi IMN applied to the grid ald where 0 11 Is filial in value alue to 01 0 1 but opposite in sign the application of flit potential when applied to the grid will cause the anto current to be reit to it 11 value 11 C or AC A C to loss than it was us when thore there was no potential ni fit tilled piled to the grid so it Is acen that a potential pati alun lip plied to tin the grid does docs not reduce the plate circuit current curr eilt us as the title positive potential increased the pante clatl elre tilt current tilts irregular of the tilbe Is intile use of when the tube ts Is used its as a detector or ut of radio signals the incoming radio aln signal nil Is it a eligil frequency current luri tnt iet us its ii llly nu au alternating difference of pu po all whose lio positive mil ill if liti Is equal neuil to 01 0 1 and whose negative vallie Is 14 egdal to tf 0 11 to the grid of tl it f e three electrode tube whose cinon curve cur la is the 11 as that chomi in fig ali vill mil in ill F fik ig IX Is falion the alternating difference of it potential applied to tile the arld through fit alio llio first quarter of a 11 cycle cle from froin zero i J 1 to a ma riega noga the five value sit at IC equal tr to 0 it tile plate circuit current will vv amry froin 00 0 0 its gallit alu 1 sit at 11 1 when no grid po in applied to at a value at y q equal lo IQ II 11 r CL during the next atif if it cycle the IK grid changed chan gei faconi a dpn ne nylic value aluc at IC 0 u o zero at L 1 alie corresponding values tit plate circuit current tire ar fly by lie file portion of r the lie plate current caim nt curve Q ail at during th the next or third quarter u of a cycle tile applied uld grid potential aa filim wro at L 1 to it juul tiM value alue ut lit M eillah to V OI 01 1 und bauges the plate circuit to in ill crew icae e frenn ill its value lue when tit lip plate potent poten tini binl la Is zero to 11 ID I 1 1 D nn art if ln orense in ili plate current equal to hl H l tle the fourth dimir ter if if a cirle acle ns na tile the grid I 1 po arapi from froin a i maximum I 1 ove re tit nt 31 1 to zero fro at N the hie plate current varies from a value S aa I 1 to t 0 T Assi lint flint vie tie curve cure as shown in tag vill VIII find and fl fig IX was with a 11 poten thil or of 40 alts on the plate then if tile alie plate current Is to tie he reduced to zero by 1 if borla ion of plate itne mith laii no potential applied t to the grid tile the plate volt ilce must lio im to avro or if a reduction of it 40 volts bauit ile be matte it if the 10 40 volts Is 18 maintained on the plate and it lugn ne gattie the potential I 1 of K E 0 la Is applied to the grid it will vill reduce tile current to zero suppose 0 K F represents five volts it call ann be seen th enthat it cli change tinge of u ive five volts aulta in fit grid potential will accomplish the same bamo result that 40 volts will in the lie plate pint circuit the ratio of tit tin voltage change cliance in the plate curmit betit Is called tile lie factor of the tube and Is denoted by the letter K in the tube just discussed tile arn factor would be 40 divided by five or eight the factor of tile the tubes available for limit beur use tit nt present Is usually between 4 and 10 the amplification factor Is a function of the dimensions and relative positions of the elements in the tube an ine incoming orning radio frequency tit nl tertia ting cut current rent applied to the grid of a of three ree elect electrode rode vacuum tube Is not only rectified fled but the variation lit in tho the plate Is multiplied by IC the amplification am pit factor of the tube tills till C helcl ro IL e pa a makes the ahr ee electrode the iffe most sensitive detector available in actual tubes the point G on oil the characteristic curves rg as shown in fig VIII all fig IX may inny not fall on such a point of the cimo that hint ilea changes lit in grid potential will calest 11 c hange ln in plate current starting with zero potential on oil tile grid it then be coines necessary to apply it 11 constant potential to tn the grid by menus of if a lintt pry in the arll gri I circuit called the C buttery lintt cry to n maintain alli the grid nt at such a point on the 04 characteristic curve cune that symmetrical changes in grid potential will cause the maximum symmetrical current to how flow in the plate circuit |
