| Show how to eliminate the grid battery expert explains method of utilizing drop across resistance cy HORATIO W LAMSON dept general ilailo company after the radio fan tins banished iho setd for U batteries by the use 0 form of plate auppl or B allm ignator lie becomes perhaps the disere to do away with the C those of rela high voltage required to bs iho power tube in the ant stage oi the audio if the plate supply outfit Is capable of providing an over all olane aquil to alie normal blaic of the tube plus the required how high voltage C battery of power stage Is banished grid bins voltage this may readily be accomplished provided a source of power Is nt annd for heating the nim ament of the power tube the circuits and equipment for do ng ahls are indicated schematically in lie figure PS represents the terminal panel of a typical plate supply unit af pf Is the power tube in question for which tl Is alic customary input transformer SF Is a speaker filter in the plate circuit of the tube to keep the direct current from pissing through the loud speaker LS liter may consist perhaps per hips of a thirty henry chole used in conjunction with a 2 MI condenser or it may be replaced by an output transformer tracing and removing needless noises in set noises in the set ome from a num her 0 some of which ann cnn be and removed quite cantli poor tube contains con taits leave aftin ban mentioned end n bit of sandpaper remedies this sandpaper the ends of he tube pronga loose wires on batteries e on alie positive storage battery terminals cause scrip ing and trains sounds loose wires in the set cin be located by the set running but without a station anid in and pressing lightly on alous wires inside the aft with a wooden rod not metal s for hie and cracking nudists DIsion nett the iserial and static will ot bome fome li with the olt ihen there lire the sounds caused by them leal aillon within worn out B hat serif ic ure iliev aw up to ard 1 testing theiu with a good volt meter old dry calls hat are the butteries for dr cell rulx ets may cause noises test too an old C Is a cause of athla sort of racket it li in the sen grid circuit or the tube hie C batur must be replaced alun ohp shows the slightest drop aiom normal thin battery virtually no current so that ll 11 comply wears out from standing around rather bihun heln exhausted by Romet lines flie ha I 1 and ecart noises when in the or audio amell flar whets iliev anav be loose from the bie have loose element or alie to alie cements amny not beell ee ll Foli jered alie contact prongs ito Is hip in saull a case hen grid lak li coln lie Is loudar alinn by nl most ni other pirt of iset or rance it the most luo e loud ard it ortan found mid this may in hv it it Is almost Imp ossil lo 10 for cue fulla i holder wire once it la bif kii so ahm a rord the act solution save old wire an fn flav oll i alefs of tre vou ingv ham the radio tall in lit box or in kotlier t ani hint run kap nn der ohp hible in n or nt UK bollam of n coset m will alwaes lid them useful in R or n odd purposes around the hoil kepp dattory plates Im li f affet to tin nils of ibur hottory occasionally to make sura hie naf well torad by thia aad solution ifill edg lo 10 areat uli he liquid louir in a atta water heer theer t ald ucla an ordinary bell transformer ta connected to the A C bouse mains amny be employed to heat the filament of the tube using a suitable rheostat ich to control the filament voltage in this way no storage battery la required for the power tube which makes it possible to add a stage 0 power directly to a dudlo set employing only dry cell bubea two in sere directly across the filament terminals are connected two resistance in berles rl and ra these may be from thirty to fifty ohms each their exact v thie within athla range Is immaterial but it Is essential eliat they be closely equal to each other so that thear center point Is equally distant from alia tube filament terminals between this benr point and the B terminal ot alio plate supply a third resistance rl is connected this Is known as the biasing resistance and it should be directly shunted with a condenser C of 1 MF note HI and 12 amny be a ohm crimination of the figure will show that the plate current of alie tube Is obliged to pass through alie rv sl stance II 11 and that the location 0 the grid return Is such that the grid will be biased with respect to the center of the filament by a voltage voltago very closely equal to the IU drop of the current through the ince if in other words alie tube Is biased by its own plate carrent this Is advantageous in that any change in pante voltage Is compensated by n proportional variation in grid bins thus maintaining automatically alie correct relation between the two value of biasing resistance the by pas condenser C Is desirable to reduce the A CL coupling between the grid and plate circuits of the tube due to the resistance which la common to both circuits I 1 he value of the biasing resistance depends of course upon the tube used and the voltage available at the plate appl terminals dv inserting n all at A the bias may be computed or it may be measured directly by means of a high resistance voltmeter connected across the terminals of ra if delred this resistance may be an adjustable unit having an operating range of to 5 ohms in goneril gc it Is not advisable to attempt to bins an but the last audio tube in this manner other tubes requiring a biasing battery should be provided with dry cell units static often misused according to authority the word static once a technical term employed by scientists and electrical engineers to denote a disturb ance in radio caused by natural electrical discharges ha come to atan anything noisy or the disagreeable 1 founds which emerge from n loud speaker it Is used in adil by he general public as well as the listeners to denote anything that Is found undesirable on the and in the street whether with reference to radio or not according to carl drelick many holsea heard over the radio are 0 course not static but ats turban cos from motors and other apparatus unshielded and probably not operating properly bureau to make meriea of tests on batteries longer life dry cell batteries are n possibility as a result 0 tests recently by the radio laboratory of the bureau of standards stin dards samples of dri ells have been collected from 20 different manufacturers for testing ihei will be measured for the almen blons of the various cells and readings made of short circuit and open circuit voltage the ests will continue for several months and may result la t giue new wrinkles in the manufacture and treatment of do cells in order to sit service from hem local station gives tip ver beaute a licit station because it bienia to be the air it t alie radio acro milestone with it hii fun nil gauge the efficiency of hl bm test liln batteries and so on llie local should just be audible for n certain amount of all anent voltage if it falls to come in with the induni tonie evening either the batter 1 s are weak or the weather bad it Is not to orue local liaa alic tip concerning condenser ivr 0 o opan n conden er AS this would destroy it in turlie process the tinfoil and sheets are to alier tl ier under licit and pressure with the aid of nn insulating corn M ind it Is ti obtain n n ew condenser conden str wase time trying U repair un old one new radio beacons new beacons wilt b to ohp equipment of the united stoics b jum the beacons are erected along both he w coasts great binkis and tte gulf of the new lenconi will brans icv totite number by the unit bcd to |
