Show tf tm raj y i A s sa 1 J uk lf w ia 5 s 13 boim ass 7 v W 73 sn sa ica fy nia ni 1 U ube alip improve to quality iv I 1 v draw raw twice A ae a au much c ofila filament cu Cui cuitene irren Tent t 1 as 7 ath others e is at same voltage Wi tage 1 4 by HERMAN BARNARD associate I 1 11 aj B in III the float audio frequency stage ll 11 lias flits long been alio llio favorite practice of radio engineers to use a power and its inclusion presented no problem to them thein the t toolkits too ook kIts its cue tra fra th expert and rut ral lied led round thep the power OWL 17 tube tha JA Q public quickly found itself information on a subject fiew dew to it the questions that rise la in the pub are naturally often addressed to dealers who autu rutn up the answer by th the particular power iube bost best suited for the installation the tube manufacturers had to take on I 1 lie ile sudden task of oV educating the deal era and their clerks to a 5 working knowledge of power powe r afif tube performance I 1 for or a short while the questions ons rained in ill thicker and faster fuster than the information IlI tIon and clerks clerk a were occar occasionally ilo nally as 88 on one Oc occasion Caston when wheal 1 ened into a radio store on 00 rul pul ton street new york city if a receiver Is asvery very powerful indeed find and delivery a henvy load to the final audio frequency tube the meets the heavy demands necessarily put upon it in such on an instance it Is to use high plate voltage all sul suitable table negative bias Is DISO comparatively high the great of receivers however are arc not lot so eo powerful that the will net fi anille lindle tile the volume in a wholly satisfying 6 ing manner showing considerable improvement indeed over the tube likely to be replaced in the final audio it Is the quality that Is tin improved proved rather than the volume in creased although larger volume some lmos results as a byproduct by product due t to 0 the lie use of higher plate voltage or a tile ease case of the also to the low plate impedance I 1 comparative table tabla the advantage of using it a power tube in tile the final audio stage Is well illustrated in the following coin comparative parn table CX A po v volts its 00 SO 90 nep neg grid erld volts 46 t 4 9 plate cur current i res I 1 t 4 I 1 nd shorted out aj i to put t dattil CIS 05 ot 04 11 12 alls this hl glier plate te voltage flinn volts for lie he ll altube tube sli since nce not hot J R and for lie die saine reason tile the A hue hag tile the rame fame mallm maximum lial plate vot voltage tage note lio ile of the in handling strong signals tit at plata volts the maximum undistorted power output la is 12 writt or about anyo find and a lait units that of tho A nt at the same binte voltage and grid bias ind nd nolice that the nt at plate volts has times the maximum ported power output of the A ki A TO DO volts I 1 hence most receivers par of the lie factory made type do not nearly overtax ae the with signal at wate plate volts the opposite condition Is quite possible it if the hie last tube were of very modest power tapa capacity city and operated only at po 00 plate volts the will give abundant service ind justifies the extra artra i 43 volf ill n battery to bring the usual no 90 volts up to volts on and small extra negative blus bias thus thim where a receiver Is I 1 equipped with for a 0 battery needed whenever a power tutie tube Is bied aed lt it Is a sir pie matter mailer to use two 45 4 r volt C batteries to supply tile the V U nog nilve grid volts and add a 11 45 volt n B battery to gain that retelling clarify ruid and richness of reproduction of the even on Is trong strong notes from local which otherwise might cause enuce blasting in the loudspeaker lond speaker remember however that the prescribed negative bias must mast be applied ot otherwise berwise tile ahe full signal voltage hence quality will be lacking inching also suitable negative bias reduces the plate current more than 50 per e cent hence makes 11 batteries last twice ao iong the higher plate voltage Is very v ery friendly toward tile lie reproduction of low notes by the reluctant Lk speaker the ta a versatile Ver atlle tube tile the while essentially a power tube tub to Is not confined in its hi use to the annl audio stage for it la Is an excellent lent radio frequency amp litter and delector do ft its superior load iona capacity makes innings it n rood good second detector in a where the power to ba Is quite high th Is suitable only for the final audio stage of broadcast receivers and Is s not to be used as radio frequency amplifier or detector it has on an outstanding value in n lip tal recommended om mended rosi position tion where there Is very considerable power to handle for t volts volta with volts w negative bins OD 20 plate J Curi current rent i drain fral lit the maximum fo ported bat jut of the a ca Z we watt agthe itie me la Is the tube that V P y baars e excessive burdens burdena 1 J T f an dAout ut straining under them y A j tj lug rendering the possibility of dismore at even remote Z volts dir drawing awing N the sane game mail t M power output aa las bin baa inda anat volta W but the grid id w ids differ alie V nt M ai rw W 4 M IN IT ulal 1 1 i fc S 0 volt blat and if dri alij ha in the nse case of the jinelle contrasted aed with the IG volt vaega atthe at ai a plate current II 11 draws more plate plat a ni doea t the he CX fit at YOU volta I 1 X thi the tuba X I 1 there ore are other power jua tubes ei 6 course the alt three principal i t ham power tubes tube sare are the OX axll tue the and tile OX CX there ere are many sets seta employing ag the so called 8 3 volt tubes throughout alloco filu ce mhd filaments of the aja 6 be an conveniently heated tit that voltage from fio dry cells the lathe la alie power tupe tube for such set sets aid add requires j a volt negative e bias at 13 VOW plate colfs volt s the und under erAnest 7 a plate current and has has a maximum undistorted output of 11 watt or about the same as 03 the the same plate voltage andas andas the at 00 plate p late blots this a very rei respectable spec table tuble showing tor for tb especially as it Is most often ofte n used in receivers that deliver a modern input t to 0 the grid of tile final audio tube the alie power t bubea U beg draw azo twice aa lucli fili filament ment current AS aa afie other tubes in the receiver that operate at tile the some filament voltage for instance the and the OX draw 5 amperage e acil ach at 6 5 volts contrasted with the 23 25 ampere file ment drain odthe of the CX A alie CX draws 12 ampere is as compared with the 00 ampere drain of the CX fit at 33 volts tb the point about power tubes Is that tile the set produces tile volume and the proper power tube la Is chosen to handle that volume without contributing any distortion As plate voltages of more than go volts commonly are used in con conjunct conj june unc tion with power tubes it Is 13 excellent insurance ronce to use a filtered output consisting elther either of an output trang foro er usually 1 to I ratio or a choke oil coll ind and condenser combination thus the direct current does not how through the lie wire of 0 the speaker gindin windings 98 and these are safeguarded from burnout it should be noted that tile the PC IC resistance of the choke coll or transformer should be low not la in excess erces of boo oiling voltage loss lose avoided also the collage lib actually applied to the plate I 1 much higher since the direct current resistance of the primary of tile proper transformer or choke coll coil la Is pot not less than that of if the speaker windings winding rs if tile resistance of the speaker windings to la ohms ond and the CX Is operated so as to draw 20 milliamperes th then en th the voltage drop or loss in the speaker r windings would be 30 volts ne arty equivalent to throwing away an entire isvolt IS 43 volt IV B bat battery teryl 1 T tic tc c capacity of tile condenser in the choke coll coil hookup should I 1 d bo be in rge preferably 4 anif or more the til e clink chok coil collor or primary of the output arons former should lifave a low direct cur rent resistance e g not more that SW ohms ohma |