Show 0 WW A W 1 1 aw how him to eliminate the grid battery expert explains method of utilizing drop across resistance by HORATIO W LAMSON Eri ginee ring dept dep badio after tile lie radio fan fail tins has huni phed the ped for 11 ll 11 bat batterley by tile the us uso of 0 quim form of plate supply or 1111 it allin tio lie bico nua meled perlin pil with frith the lio deidre deglio to do dwity with the 0 batteries especially kliore of ral lively high voltage required to blin blag flip power bover tube in ili the lite lust last of tile the audio amplifier rf if tile lie pinto supply outfit la Is capil ble of 0 providing nn all civet ull oil ottury ot ture to tho tio manial anite of ho tube plus plim tile required PS A 1 PT T qa 0 1 as 0 RJ C V AC ta RA how high voltage Vol C battery of power stage Is if banished grid blag bias voltage thin may readily be provided a separate source ot of power Is ot at liand hand for heating in tile the flim ament of tho the power tube tho the circuits nud and equipment for ot doing ing tills uro are indicated schematically in ili the figure O PS represents presenta re tile terminal panel of a typical plate supply unit PT la Is the power tube tit in question for which tl TI Is the customary input tralis former fori niT SY Is a speaker liter filter in tie the plate circuit of tile the tube to keep tho the direct curre current at front from passing gli the loud speaker 13 18 tills this liter filter muy may consist perhaps ILI imps of a thirty henry choice used in conjunction with a 2 ml MF condenser or it may inny bo be replaced by an output transformer an ordinary ord loory yell LWI ringing transformer ta 1172 connected to the A C Q house ninada may be employed to heat tile lie 0 lait filament e nt of tile the tube sang a rheostat alth to control tin filament vol lit it tills way no buttery li required for the powei power tule whirl lillikos likes lil it possible to wid d a singe i of power n dire elly to a radio ampt t employing only dry lra abe two tw resistance in series directly across the filament lebrint enli are arc connected two vo resistance ln in ceilea III odd and those way be frob I 1 WHY 10 lo fifty olian ench their duct tuluo within vl llin lails lis nicie ix IK but it Is essential billat illat they to ho clowley equal to 0 o each other so go that their wn cell tap point la ix distant front the tube flin ment between tills center point and tile 11 terminal nill nl of the plato supply a third resistance 13 if Is connected Is in known as aa the resistance reals dince tind ond it should be directly with a conden condenser her C of I 1 MK MF note H and aind 12 wily lc ile a ohm lamination 1 of uio the figure will show tho file plate current of ube tube la obliged to poss through the re sla tance it II orld ind that dint the location of the grid rid return Is in lucli flint tile the grid will be biased negatively with respect tolie lie center of lie moment by a very lery closely equal to the lite III drop of tile llie chite curant through the in other words tile tube la Is blamed by its fit own plate current tills thin Is 18 in that any ditmire chiun T in n plate voltage voltago Is campen gated liy fly it variation in grid bins bills flur cally tile correct relation between the ills two value of biasing resistance tin the hv by pa q C ih 14 to reduce the A G coupling between the grid iti ld imil plate Ir cults of tile the bubp adue flike to the which Is it co common ninion to both 0 lul til a L ilik altie u af lite blu ng resistance of apoll jie he tube used and ho fie voltage available nt at the plate ly by inserting it nh fall meter nt at A tile the bins bias may ila be computed or it may be mett directly by of a high resistance volt ampter connected across tho the terminal of US if desired tills resistance may bu be tit un adjustable unit tint having up act operating abing ronge of SOO to ohms in fix gene general rul it Is not advisable Dihl to attempt to bills tiny any but the last audio tulio tube in ill ih tills ig manner other tubes requiring a biasing buttery should ix be provided with dry cell uneta |