P ^ DETERMINATION OF. Part I. Doner, W3FAL. maximum ratings and typical operating conditions. service are given below. This procedure may

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1 1 AT P ^ -, r A PUBLICATION OF THE RCA ELECTRON TUBE DIVISION VOL., NO. 1, RADIO CORPORATION OF AMERICA DECEMBER, 1 DETERMINATION OF TYPICAL OPERATING CONDITIONS Fr RCA Tubes Used as Linear RF Pwer Amplifiers Part I By Claude E. Dner, WFAL RCA Electrn Tube Divisin, Lancaster, Pa. During the past few years, ham interest in single-sideband transmissin has been n a cntinual upswing. As a result, numerus articles have been published n the thery and cnstructin f linear tride and tetrde amplifiers. While these articles have discussed classes f tube peratin and cmpared grid-drive t cathde-drive circuits, nly a handful prvided design infrmatin fr adapting tube manufacturers' data t available cmpnents r t the amateur's specific requirements. Included amng the "selected few" was an article by A. P. Sweet, which appeared in the December, 15, issue f HAM TIPS. It presented such infrmatin in the frm f step-by-step calculatins fr use in cnverting published maximum ratings t typical perating cnditins. Nw, six years later, having recgnized the need t bring this design infrmatin up t date, HAM TIPS is pleased t ffer here Part I f a tw-part article prepared by WFAL. This first part extends the calculatins t include cathde-drive (grunded-grid) peratin f tetrdes and trides in class AB, service. In the next issue, Part II will cver the prcedure fr calculating typical perating cnditins fr class B peratin f trides r tride-cnnected tetrdes in a cathde-drive circuit. Sample calculatins are based n published data and curves fr the RCA- pwer tetrde. Als included is a chart which lists fr several widely used RCA pwer tubes. maximum ratings and typical perating cnditins Class Operatin f Tetrdes (Grid-Drive Circuit) When it is desirable t perate tubes at cnditins ther than thse given in the published data, typical perating cnditins can be calculated frm the maximum ratings and characteristics curves. The calculatins required fr class peratin f a tetrde in grid-drive service are given belw. This prcedure may be adapted t tride tube types by eliminating the terms E c2, I C 2, i' C 2, and SI frm the calculatins. (1) Make sure that E b is within maximum ratings. (E b is ne f 21 symbls defined n page 2.) (2) On the average plate-characteristics

2 : 2 RCA HAM TIPS December, 1 curves, select a pint near the "knee" f the curve fr zer cntrl-grid vltage; recrd i' b and e bmin. Frm the average screen-grid characteristics curves, determine i' c2 fr this pint ; recrd E c2 fr the curves used. () Calculate I bms : Ibms = i' b/. () Calculate PD: PD = (I bms/) (E b + ^hmin ) (5) Calculate SI: SI = E c2 i' C2/. (6) Calculate PI: PI = E b I bms. () Check the values btained in steps thrugh 6 t determine whether they are within tube ratings. If either I bms PI, r PD is ut, f ratings, select a pint slightly lwer than the riginal pint n the knee f the curve fr zer cntrl-grid vltage and recalculate steps E b ebm in E c2 E cl ecm DC plate vltage (with respect t cathde) Minimum plate vltage necessary t prduce the required peak ( frm the characteristics curves) DC screen-grid vltage DC cntrl-grid vltage Maximum cntrl-grid drive vltage needed t btain the required peak plate at a given minimum plate vltage E'g Peak value f cntrl-grid vltage swing Ibms Maximum signal, dc plate I b Zer-signal, dc plate i' b Instantaneus peak plate I c i Maximum-signal, dc cntrl-grid I c2 Maximum-signal, dc screen-grid i'ei Instantaneus peak cntrl-grid i' c2 Instantaneus peak screen-grid PD dissipatin at maximum signal dissipatin at zer signal PD PI pwer input at maximum signal PO Pwer utput at maximum signal Pft Feed-thrugh pwer at maximum signal (cathde-drive peratin) Driving pwer at maximum signal DP SI Screen-grid input at maximum R p signal Effective rf plate-lad resistance 2 thrugh 6. If nly SI is ut f ratings, select a pint slightly higher n the knee. If SI and either I bms PI, r PD are ut f ratings, select, a lwer value f i' b (either in the negativecntrl-grid regin r at a lwer screen-grid vltage) and repeat steps 2 thrugh 6. () Calculate PO: PO = PI - PD. () Calculate I b : I b = It>ms/5. () Determine E c i frm the plate-characteristics curves as the cntrl-grid vltage at which the plate vltage is E b and the plate is I b. () Calculate E' g : E' g = E c i + ecm. This value f E' g is equal t the abslute value f Ed (the straight lines arund this term indicate that its plus r minus sign may be ignred) plus the algebraic value f ecm (include the sign). If the pint selected in step 2 was n the curve fr zer cntrl-grid vltage, then ecm is equal t zer and E' g = E C1. () Calculate I c2 : I c2 = i' (. 2 /. (1) Calculate DP: DP= E'gi'ci/*- (Fr peratin, i' cl equals zer ; therefre, DP is als zer.) This value f DP des nt include rf tube and circuit lsses. The pwer available frm the driver, therefre, shuld be at least times this value in grid-drive peratin. Because tube driving pwer is zer, determine the apprximate driver-utput requirements frm published AB 2 typical perating cnditins at apprximately the same E' g and perating frequency. () Calculate R p : R p = E b /1. Ibms. * * * Example The fllwing example illustrates the calculatin f typical perating cnditins fr class tetrde peratin f the RCA- in a grid-drive circuit (1) The maximum plate vltage rating is vlts. (2) Frm the plate-characteristics curves shwn in Figure 1 (E c2 = vlts), select a pint PI n the knee f the curve fr zer cntrl-grid vltage. At this pint, i' b is.6 ampere and e bmin is vlts. At the crrespnding pint n the grid-characteristics curves shwn in Figure 2, i' c2 is equal t. ampere. () I bras = i' b/ =.21 ampere. () PD = (I bms/) (E b + e bmin ) = (.21/) [ + ()] = watts. (5) SI = E c2 i' c2/ = () (.)/ =. watts. (6) PI = E b Ibms = () (.21) = watts.

3 December, 1 Table I: Ratings and perating cnditins fr RCA tubes used as linear rf pwer amplifiers. Tube Type 2E -rt A_1 OCA -A A Class f Operatin AB 2 Service (E b) Grid-N. 2 <Ec2> (Ibms) ma Maximum Ratings Abslute Values Input (PI)- watts.5.5 Grid-N. 2 Input (5\)-watts Max. -Signal Dissipatin Grid-N. 1 + Grid-N. 2 (l c i c2) ma (PD) watts + l.5.5 Grid-N. 1 Resistance hms 1 K AB K AB UUU DUU U DC AB K K K K (Eb) Grid-N. 2 (Ec2) 1 1 c r\r\ Grid-N. 1 (Eel) Peak Grid-N. 1 (E'g) qq JO 2 5 Zer-Signal (lb) ma 6 fio 62 1 Typical Operatin (lbms)- ma C\JJ 5 Grid-N. 2 (lc2) 1 1 c 1 ma Max.-Signal Grid-N. 1 + Grid-N. 2 (Icl-Hc2) ma AB B 1 2B Natural Cling AB 2 pp<s 2A K K K K A B K X<J A / K AD. At>2 2 AB 2 B* 1 1 5fi 1 J 1 1 q K K K K 5 K *Tride-cnnected cathde-drive peratin During shrt perids f circuit adjustment under "single-tne" cnditins, the average plate may be as high as ma. Peak envelpe pwer 2 /U cc li i izu n ) Drive Pwer (DP) -watts ft A Pwer Output (PO) watts /U

4 December, 1 RCA HAM TIPS 5 Figure 1: Typical plate characteristics f type. 1 PLATE VOLTS 1 1 () Because bth PD and PI are abve the maximum ratings fr the, a lwer value f i' b must be used. Select a pint P2 belw the riginal pint n the knee f the curve fr zer cntrl-grid vltage and recalculate steps 2 thrugh 6. At the new pint, i' b is. ampere and Cbmin is 1 vlts. At this pint n the grid- CO LU QC LxJ GL Ef = 6. VOLTS GRID- N. 2 VOLTS = GRID-N.l VOLTS = EC, ^ CM O CM 6 z I CD OC O Figure 2: Typical characteristics fr type. i 1 PLATE VOLTS 1 1

5 6 RCA HAM TIPS December, 1 characteristics curves, i' C2 is.1 ampere. I bms =./ =.1 ampere. PD = (.1/) [ + (1)] = 1 watts. SI () (.1) / = watts. PI = () (.1) watts. All values in steps thrugh 6 are nw within maximum ratings, and the calculatins may be cntinued. () PO = PI - PD = - 1 = watts. () I b = Ibms/5 =.1/5 =. ampere. () Ed can nw be determined frm the plate-characteristics curves as the cntrl-grid vltage at which the plate vltage is vlts and the plate is. ampere; E^i = - vlts. () E' g = Ed + e Cm = + = vlts. () I c2 = i'ca/ =.1/ =. ampere. (1) DP = EW2 = () ()/2 =. A suitable value f driving pwer can be determined frm Table I. Fr the in service, a typical value f watts is listed. () R p = E b /1. I bms = / (1. X.1) = 6 hms. * * * Table I shws the maximum ratings and typical perating cnditins fr several ppular RCA tubes in linear rf amplifier service fr single-sideband, suppressed-carrier service. It shuld be remembered that the typical perating cnditins shwn by the manufacturer (r calculated by the preceding methds) are nly apprximate. Minr adjustments are usually made in actual peratin by slight variatin f the cntrl-grid bias r screen-grid vltage. In linear rf amplifier circuits fr single-sideband, suppressed-carrier transmissin, it is particularly imprtant t check the actual perating cnditins when the transmitter is first set up t assure that linear peratin within the maximum tube ratings is being btained. Infrmatin furnished by the Radi Crpratin f America ; ; 1ST fringements f patents r ther rights f tlftab pafll^l which is believed t be accurate and reliable. Hwever, n re- may result frm its use. N license is grantpqpy iggjeatin spnsibility is assumed by RCA fr its use; nr fr any in- r therwise under any patent r patent ts ^ «$CA. ffifr GEORGE D. ARSY CO., IN nva + L»i~y WHEN M*f lng««lancaster Lebann place PsflteE igp S e*> Frm yur lcal RCA distributr, headquarters fr RCA receiving and pwer tubes. RCA HAM TIPS is published by the RCA Electrn Tube Divisin, Harrisn, N. J. It is available free f charge frm RCA distributrs. Harvey Slvik, Editr FORM 5 REQUESTED