Show i af pf P mi r i ay iy am W M I 1 I 1 L X J AW 4 0 v IS att w exco 1 I A I 1 ley ta tf n i 00 10 1 1 to V re 4 7 11 1 7 00 01 K tl 1 y t I 1 leo ak y h I 1 LJ a io 60 0 o bj aj 1 ioa aa 4 rutt PLATE vein copyright FIG 2 1 how to calculate tube tub contant constants plate plat ance Is ie aaker at talked with a simple apparatus that it ft Is if not beyond the means mean of tip average radio fin fi n to calculate tile the constants of his own tubes Is amply proved iq if flip enlightening article on this subject by helth henney labors labora tory ory expert jn n the number of radio madlo broadcast magazine the only apparatus necessary besides the tube socket rheostat batteries and perhaps a potentiometer to control jarld bias consists of two meters a double range ranee voltmeter and a meter the former should have ranges of from 0 to 10 and 0 to volts chife the should rend read up to 10 mlle and as higher rending readings may be required of it a shunt will be necessary the I 1 he object of a shunt Is to enable higher readings than the maximum figure marked on the dial face to be read in his radio broadcast article mr air Heft hacnney iney explains how flow the amplification factor plate impedance mutual con duchance duc tance and d cand c and a c may be found here it Is intended briefly to outline his method of ariev ling at the plate impedance suppose it Is desired to obtain the above characteristic of a standard A tube we first of all set up our apparatus as shown in tile accompany ing MR fig 1 here a voltmeter la Is shown connected across each of the three sets seta of butteries batteries but of course our one double range meter Is all that la Is es for only one reading Is taken at a time tile grid gild battery should prof erubey erual consist of a storage buttery battery or be several veral 1 volt batteries so that 2 volt or I 1 volt variations tire are possible A potentiometer is not shown in ohp I 1 diagram but one may be used to ad van altage antage tage for varying the grid bias how to proceed the llie setup set bet up complete we place our voltmeter neter across the filament posts of the socket and adjust the jhc rheostat estat if un 0 tit til the meter rends read 5 volts cilta for our first curve that shown as ERO on the chart we shall omit the grid battery eg represents grid bias having obtained a piece of graph paper and marked it off similarly to tb the chart shown herewith we are ready to proceed we adjust the B battery voltage in 22 volt steps and read the plate current for each step thus we are able to plot a curve such ns as that one marked ega on the ac chart to get tile the plate impedance at zero eero volts grid bias then we utilize the fol lowing formula in which up kp represents the plate impedance change in plate voltage ft up change in plute plate current referring to our chart we read that hat w with ith a zero pro bias a plate voltage of 11 6 volts gives us it a 13 plate current and it a 48 volt plate voltage gives us 3 plate current vv we c put down that hut information thus ilium plate 1 plate late current urr mt 1213 11 13 48 1 3 is 78 volts change 10 mi i immke we U must use volts voits ahins and am pert peres a in our formula above and so up e amert our 10 tall mil to amps binti ule in the formula 78 ftp jsck 7 00 olima ohms therefore rii the he plate impedance tit nt zero volts volta grid blai bias Is t TSOO ohms L fair l air ther curves may be drawn to obtain the plate impedance at various grid beasom find and these are shown in hg flig 2 as ega I fg ka 4 EKS ega EK S and nd eg 10 tandem tuning condensers condenser tandem tuning of condense con dener to de cheatw breare the number of separate con tins has become quite mention common there are some fundamental facts lucern ou cern ing tandem tuning taping which auit be considered it if results are to be obtained and these tire are inter outlined lo in a short article to la the radio magazine the output and input chars in ID which the framed circuits work must be exactly similar to in each stage before the condensers condenser way may be successfully suc cesa banged ganged in a standard circuit with two gages of tuned radio frequency it Is not a biffl cult matter to gang tile the condensers across the lie secondary colls coils of the transformers transform ees in the grid circuit of tile the 6 second em nil radio frequency and detector stages providing tie the rolls coils iriv are matched it would nut not be possible bo however wever to control the condenser tun un ing the grid circuit of the first radio frequency tube obe by the he same knob which contres the other ivro condris nii am eves though the coils and cm ilenberg ilen serg in this circuit were matched with tue ane others the reason for this Is simple while tile the circuits controlled by the he second nud and third condensers by virtue of the fact that are both fed from the of a preceding tube tile the circuit tuned by the first condenser la Is being energized by the antenna and ground system and Is therefore unlike the others othera in characteristics in the radio broadcast article a diagram jig 1 shown which makes possible the tandem tun tuning irig of tile the three circuits by means of the addition of an extra tube ahead of resistance si anee its ita grid circuit being tuned to elie output of the new tube Is connected the former input of the previous fars r f stage thus thug the input of the two r f stages and the detector circuit are all connected to the plate circuit of a preceding tube FIG I 1 C MX MA 0 a 0 0 10 volts A 0 loo 1 V C copyright broadcast 1926 1 diagram showing how to set up the th apparatus nod providing the colls coils and condensers ell are matched they may be tuned by one three gang cane condenser it would be possible to gang the three condensers without adding the tube but this would require extremely accurate cutting of the condenser plates so BO as to compensate for any effect of the antenna ci renit this Is a difficult job and lt it Is preferable to either retain two controls or to use an extra tube ammy so called single control receivers are equipped with some compensating device which permits exact tuning of each circuit to resonance in some eases cases tills this device consists of a small midget connected in parallel with one of the main tuning sometimes the stationary plates of one if f the con dil users tire are mounted on oil a plot phoi so as to permit more accurate iu unite tuning hut flut no receiver that has mich huch tin an adjustable feature can be cabled a single control set |