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                                                      USEFUL INFORMATION FOR USERS OF TEKTRONIX INSTRUMENTS


NUMBER 24                                                                 PRINTED I N u . 5 . ~                                         F E B R U A R Y 1964




                                                                                                  er,   Accessory



Infrod~{cfion                                                     Tlie conventional current transformer with    in the spnce between tlie inner and o u t e ~
    Modern technology requires measurement                     1;imin;~tetl core (Ref. 2) is useful up to       contluctor of n coaxial transmission line
c a p a l ~ ~ l l t ~ Ini the f ~ a c t ~ o n a n.wosecond
                      c                         l              a few kc. Tlie tape \vourid version extends      of impedance Z, (Figure 1 ) . For simplic-
(lo-' second) a1 ex D ~ o d e s\T 1t1i sn ~tclimg              tlie frequency response :md phase correla-       ity only lialf of the IcngLh\vise section is
t~mes     \\ell under 100 p ~ o s e c o n d s(lo-'' sec-       tion to approsinlately 100 Icc.                  represented. The H (magnetic) field will
o n d ) :uid transistors n ~ t l if t (cut off ire-               If the design of a current transformer        terminate in a current sheath J in the eir-
quenc) ) of over 1000 Mc nl c presently a\ all-                is based on a T E M (Transverse Electro-         cular winding
able
     Tlie s a m p l ~ n g oscilloscope prov~des ;In
                                                               magnetic Mode) approach however, the              (Curl I l =         + J since
excellent tool f o r tlie ol~servat~on these       of
                                                               Insic f requcncy limitations are overcome                       b t
                                                               and fractional nanosecond speeds can be           inside the Ivinding .'. curl H   = J.)
phenomena provided the signals are pre-                        nchieved.
sented in a 5On characteristic impetl:mcc                                                                        Also, since H is proportional to I, then
system. Ilowever, it is \cry seldom that                                                                          $5 = I and a current I will flow in
 one can load a circuit with 50 either in                      Tlzc TEjlI Czirrcjzt Trnusforii~er                Z, for a single turn winding. A t X3 the
parallel or in series without disturbing it                      A single turn circular xitiding is inserted     current I in the single turn winding will
beyond use. Therefore, one has to provide
 means to extract the voltage and current
 waveforms from the circuit ~vithout dis-
 turbing the circuit to any great extent.
 T h e output of this device should present, to
 the sampling oscilloscope, an undistorted sig-
 nal on a 50 n level.
     I n tlie case of voltage measurements, a
 good high frequency resistor (Ref. 1) map
 be selected. Provided it is placed in a
 proper environment, this type of series probe
 will perform rather xvell up to 1000Mc.
  F o r the current waveforms, however, the
  solution is more complicated. Conventional
  current monitoring devices are restricted
  t o relatively low frequencies either by basic
  limitations or b y strap parameters. For ex-
  ample, the Hall potential in a Hall device
  is established in approxitnately                      sec-
  ond. Hoxvever, its inherent stray capacity
  and flux-linliage patterns prohibits its eco-                 Figure 1 . A single-turn winding inserted in the space between the inner and outer conductor of
  nomical use above a few Mc.                                   a coaxial transmission line of impedance Zo.


                 T e k t r o n i x Instrument-Repair Facilities: There is a fully-equipped a n d properly-staffed Tektronix I n -
 A-2205          strument Repair Station near you. Ask your Field Engineer about T e k t r o n i x Instrument-Repair facilities.                          2/64
I-cgener;\te I 3 in e c l ~ l l ~xignitutlc :lilt1 :1c-      \\'e have a trnnsiorrner \\.it11 one pri-                 2 Z, c:il~le, a s shown. I-Io\vcvcr, this will
c o r t l i ~ i a to tlic principle o i super-positio~i   m i r y : u ~ ln seco~itlary t u r i ~ s (Figure 2 ) .       work only i o r a time ccluiv;~lent to tlic
I;= =   r<, - IZ,.                                        I i we introduce a cui-rent step I in the                    double tlel;iy time ( 2 T ) in one Z , c;\ljlc
                                                          primary \vintliiig, \ye will i~itroduce n cur-               1)ec;lusc niter t h t the gener;itor will he              1
                                                          rent step i,, at tlic s c i i i ~ c timc antl o i equal      shorted. One c:ui extend this timc spati
                                                          m;\gniti~tlc in :\I1 n t u r i ~ s . T h e step i,, intro-   1jy placing an impetl;lnce in the short cir-
iiidic:ltiiig tli:lt tlie inipedmce Z I is ef-            duced in a particular turn \\.ill propngatc                  cuit loop - here done by means of a fer-
fectively plnccd in series \\.it11 Z,,. (Tliere-          iii n tr;~iismission-linc ~notlea r o u ~ x ltlie core       rite core (Iiefs. 6 antl 7 ) .
f o r e , to iii;\int:li~i ;I iirst ostler m:ltching,     in both tlirectioiis :11itl so \vill ;ill steps in
tlie ratio o i the tli;\ii~etcrsof tlie inner :md         every turn. Tlie resulting output Jvave-
o u t e r contluctor plst S. in the S direction           forms ;it tlie secondary terminnis of tlie
sliould 1)e reduced to I)e equal to Z?.) A sec-           transforiiier will, therelore, look like Fig-
ond order c;qncii~ve reflectioii occurs bc-               ure 3 indicating a "pusli-pull" mode oui-
cau5e tlie E field in going f r o m S1 to SJ
is confined l~ct\veen tlie inner conductor
anti tlie winding and betiveen the outer
 c o ~ i d u c t o r2nd tlie winding.
    Seglecting the winding transit time,          for
a n "n" turn \\inding       YJ   = I \vodd       still
6 b l d ; lionever, I \\.ill be a current I/n     per
t u r n . Tlie current through Z1 is I/n         antl
t h e series voltage drop reflected in            the
                              I
                              11   -      I
original    E   field is    ---- - -
                                   nZ
 Therefore, Z? =
                    T




     T h e reflected impedance is proportional
 t o 1/n2, similar to the conventional trans-                Figure 3.     Output of twelve-turn transformer.
 f o r m e r A true mathematical deriwtion of
 these results amounts to a dolible hountlary             put. Here, then, w e have tlie first basic
 value probletu ( R e f . 3 and I ) and is quite          limitation: tlie risetime of tlie output wave-
 involvetl. I-Iowcver, this is not essential              form will be approximately n times td,
 t o achieve a basic understanding o i tlic               where td is tlie delay of one ~vinding.                         Figure 5.   Twelve-turn bifilor winding.
  functionitig of a T E M transformer.                      Tlie second limitation of tlie conventional
     U p to this point w e really have not                current transformer is the fnct that there                       I n Figure 5, rather t1i:ln ~ v i n dan n turn
 solved all basic limitntions of the tmns-                is a certain :\mount of stray cap:lcitance                    single winding transformer, t\vo windings
 i o r m e r , ) e t tlie prccetlmg is essential for       (C,) antl inductance (Ia,). This will form
 t h e untleritand~ng of the methods itivolved            a distributed L-C circuit that ~vill resonate
                                                                                                                                        I1
 in solving them.                                                                                                       each having          turns have been wound
                                                           at a
                                                                                     0.33
                                                                    frequency below - - (equivalent
                                                                                      -                                                 -
                                                                                    n s ttl
                                                           3-db point due to tlie first limitation) antl,               bifilar, a s sho\vn. T h e four output volt-
                                                           therefore, give a poor transient response                    ages a r e then added and supply one single
                                                           especially ~ v h e n n is large.                             ended signal. Tlie addition is performed
                                                                                                                        n i t h tlic trans~nission line addition tecli-
                                                                                                                        nique. However, f o r practical reasons tlie
                                                                                                                        wires a r c kept very short and, therefore,
                                                                                                                        tlie double delay time (2T) is short. One
                                                                                                                        depends m:linly on the isolation provided
                                                                                                                        by ierrite beads placed in the short circuit
                                                                                                                        loop. Leads should be kept to the same
                                                                                                                        length t o assure time-coincident addition of
                                                                                                                        the signals. By doing this w e have acliie\wl
                                                                                                                        two improvements ( F i g u r e 6) :


                                                              Figure 4. A step V, placed simultaneously                  ( a ) T h e risetime of tlie output pulse, due
                                                           on two Z, cables, odds the two steps to a 2V                        to limitation one, has been reduced
                                                           step into a 22, cable.                                              f r o m n s td to n/2 s td ( T h i s is not
                                                                                                                               exact because the turns in this case
                                                             In Figure 3, if a step V is placed simul-                         nil1 be sl~glitly longer; therefore, td
                        b    b                             taneously on the two 2, cables, one can                             nil1 be sl~ghtlygreater. However, this
     Figure 2. Twelve-turn transformer.                    add these t ~ v osteps t o a 2 V step into a                        effect is small.)



                                                                                                                                                 @ 1964 Tektronix, Inc.
                                                                                                                                                    A I,   "!_L._   D^_^".,^-l
                                                                                9 turn
                                                                                                                                      trans-

                                                           ulser
tunnel                                         661
                                               452
diode
                                               5Tl




  ( 0 ) Pulse direct to 452.                                 ( b ) Pulse coupled to 4S2 via o straight            ( c ) Pulse coupled to 452 via 3 x 3-turn
                                                                   nine-turn transformer on o 1/2" dia.                 transformer on a 1/2" dio. by ',&" core
                                                                   by ',&I' core.                                        [some core as used in ( b )   1.

Figure 6. System used to obtain these waveform pictures: Tunnel diode pulser ( ~ 3psec risetime), Type 661 Sampling Oscilloscope with a Type 452
                                                                                   0
Dual-Trace Sampling Unit and a Type 5T1 Timing Unit, and a Type C-19 Camera. Sweep Time/cm: 0.2 nsec.



( b ) T h e transient response, due t o limita-                                                                   Generally the low permeability ferrites
        tion t ~ v o , Iias been improved due to                                                                have a Iiigli resistivity and the high perme-
        the fact tliat the stray capacit;uice has                                                               ability icrrites a low resistivity. Tliereiore,
        been reduced since the trvo windings                                                                    the high permeability ferrites liave higher
        at every point on the core move in tlic                                                                 loss than the low permeability versions.
        same manner volhge-\vise [ i r (reso-                                                                   Some typical high frequency ferrite materi-
        m n t irequcncy) proportional t o l / ,ic]                                                              als a r e :
        while the inductatice and resistance stay
        essentially the same.                                                                                                         Periileabilifg R h o ( Q 2111)

  Note that a t DC the two windings a r e in
                                                                                                                Ferroscube      101       200-250           >   10"
                                                                                                                                102       250-100           400-600
series. Tlie output voltage is the same a s                                                                                     101       300-700           250-150
that o i a conventional 11 turn transformer.
One cnn use niultiplc turns througll the iso-                                                 FERRITE           Kearfott    hfX30      4,000-6,000          300
                                                                                                                            bli\'60    5,000-10,000         230
Intion 1)eatls t o obtain a large time constant.                                              BEADS
Kote also tliat one is not limited t o 2 rviiid-
ings of n/2 turns per I\-inding. One can                                                                        T h e Design of a T E M Current Trans-
use n windings o i 1 turn per ~vinding (as                                                                      f o1.111~~
long as n/a is greater than 1 and a real                                                                           In order to design a Iiigli speed current
number). T h e liiiiitntion is 11 rvindinns of                                                                  transformer, one Iias to consider several
1 turn per ivintling and there the risetime                                                                     factors; transformer ratio, risetime, lo\v
is equivalent t o 1 s td o r the total prop:\-                                                                  frequency time constant, space ava~lable,
gation titnc around tlie core, wliichever is                                                                    impedance level, ctc. T h e lumped constant
greater (Figure 7 ) .                                                                                           equivalent circuit is represented in Figure 8.
    One can i~uiltla t r m s f o r m e r \vitli :I large                                                        H e r e R, = R, n ? ; L = I-, n'
                                                             Figure 7. Eight-turn multifilor winding.
~ l u i n i ~ c r tusns to get n long time const:int,
              of
but at the sntne time one c:r!i get a very
                                                                                                                   R, is assuiiiecl to be a constant propor-
                                                           o i the r\.iiiding. T o cxtend this lime usu:illy    tional to tlic core losses and expressed in
iast risetime and good tr:insient responsc,
                                                           i o r higli frcquency :ipplicntic,iis n ferrite      olims/turn2. I n practice, lio\vever, one might
ns \\-ill Ije esplai~letllater.
                                                           core m:iteri:\l (Ref. 5) is used. Fcrrites           Iinve to use a tlifierent 13, i o r high fre-
                                                           a r e sinteretl innterials, generally of a l m i -   quency (and lo\\- frequency) calculations de-
Core -1ftrterinl
                                                           cally spinel cryst:illinc structure consisting       pending 011 material and bandrvitltli. Tlie
  Unlcss a core rvitl~ a permc:il~ility >1 is              o i I\IOFe20, n-liere Bf can be o i any of           values given .1 the ferrite manuinctilrers
                                                                                                                                ,
inserted inside tlie \\inclings, the tr:uisiornicr         tlie follorving elements: Co, Xi, hIn, Cu,           generally refer to the lorv-frequency losses
action is limited t o t h e double t r a l i s i ~time     Mg, Zii, Cd.                                         of the material. They liave no consistent
                                                                                                            tinie constant since a t low frequencies the
                                                                                                            turns appear in series. T h e transformer
                                                                                                            may be used for current measuring purposes
                                                                                                            a s well a s f o r tnatcliing t ~ v opoints of dif-
                                                                                                            ferent impedance levels. I n either case, the
                                                                                                            transmission line will have a voltage Ivave-
                                                                                                            form a s well since tlie characteristic ini-
                                                                                                            pedance is always greater than zero. I n
                                                                                                            order to prevent capacitive coupling of tlie
                                                                                                            voltage waveform, tlie transformer has to
                                                                                                            be u d l shielded by a ground plane between
                                                                                                            tlie center conductor and tlie transformer.
                 Figure 8. Lumped-constant equivalent circuit of a current transformer.
                                                                                                            -4 perfect shield is not feasible, since tliis
                                                                                                            \voultl amount to a shorted turn on the
correlation \\-it11 tlie frequency vnlucs of R,,.       \\-ill he limited to a liiglier fl-ecluency. I t    trnnsformer. However, satisfactory shield-
T h e r e f o r e , these need to 11e nie:isuretl for                                                       ing can practic:illy he :~cliieved by leaving
                                                        can he readily verified that :
individual materials. '\;alucs vary from 20                                                                 a narrow gap in tlie shield.
f2/n2 to > 500 Il/n2 depending on core ma-
t e r i a l and dimensions.                                                                                 References
    Id,, is a constant proportional to tlie per-
                                                           Tlie phase shift \\.ill be :ipprosimately        1. C. N. \\'inningstad, I S A N D O U T O F
nie;kbility of tlie core, tlic cross section and
                                                        8.1" at tliis frequency. If :I m:lsitiium pli:~se      C I R C U I T S \\'ITI-I P R O R E S , Proceed-
t h e magnetic length. F o r a cylindrical core
                                                        shift of lo is required tlie lo\ver frequency          ings of the Xation:ll Electronic Con-
w i t h outer diameter D, inner diameter tl
                                                        response should be limited to a still liiglier         Icrence; 1610, pp. 161, 1963
and length t, tlie intluct:mce/turn' can be
                                                        frequcncy. Ii?; performing tlie necessary
estimated b y : L , = 0.2 pt I n D/d s lo-"                                                                    F. I<. I-Tarnis, EIdECTRICI\12 ME.-\S-
                                                        c:1lculntions one finds :
pH/n2                                                                                                          U R E M E S T S , \\rile,;,   pp. 542-564
   Z,,,   =   the transformed impedance.
                                                                                                               Reitz - Milford, F O U Y D A T I O S S O F
   T h e low f requcncy cut-of f is determined                                                                 ELECTRO-MAGNETIC                 THEORY,
b y the L / R time constant.                                                                                   .-itldison \\'eslep, pp. 210-214
                                                            A s a practical example, n transformer
  T h e re5ponse ~ v i l lbe 3-(111 do\\-n i f :        \\-it11 a low frequency 3-db point of 10 kc            Morse - Feslibach, M E T H O D S OF T H E -
w L = 2 x f L = R, where R is t l ~ e total             \\-ill have n 1% amplitude accuracy above              ORETICAL PHYSICS
resist:uice R,, in parallel \\-it11 L.                  7 0 1 ~  and less than l o phase shift above
                                                        570 Iic.                                               Polydoroff,        HIGH-FREQUEXCY
                     nT,,RI,
           R,, =                                                                                               M A G S E T I C X 4 T E R I A L S , \\'ilep
                   n'R,,   +  R,.                          F r o m the low frequency point of view it
                                                                                                                C. K . \\'inningstad, SAXOSECOXD
                                                        is tlesirablc t o have a Inrge numl~erof turns
                                                        to m:~lie I, and R I 1:u.g~. A s previously             PULSE       TRASSFORNERS,          IRE
                                                        sliolvn, this limits tlie risetime.                     Transactions on Kuclear Science, h/larch
   A t tliis point there will he a 45" phase                                                                    '59
                                                          Ii?; splitting the ~vinding into several
 sliiit through the trnnsiornicr.                       multiiilar turns, as previomly outlined, one            Lev% - \\'ells, M I T L I M I C R O S E C O N D
   I f accuracy of 1% is required in tlie               can maintain the risetime for high speed                I'UL2SE     T E C I H X I Q L E S , Pergamon
 transfer ratio, the low frequency response             operation and still have a large L and long             Press




                                                          One solution to this problem is to use                "Scope Pad" consists of twenty, trans-
                                                        :I slieet of "Scope Patl". This is a unique          lucent, :ldlicsive-lxd;cd sliects ruled with a
                                                        product ni:liiuiacti~rctl :lnd tlistri1)utetl 1,y    graticule-line g r i d .-\t tlie side of each
                                                        Eiisc:l, Inc., P . 0 . 130s 253, S e w YOI-li,       slieet a r e spaces for tinie and amplitude
                                                        N e w York 10023.                                    data.

    If you \\-anted to malie a record of a
 repetitive \v:~veform displayed on the crt
 of an oscilloscope and you didn't have a
 camera, you could stand 11:ick wit11 easel
 ;md pen, hold up your tliunib in Ren1br;lndt-
 style and slietcli alvny. O r , >-ou could place
 :I sheet of translucent pxper over the face
 of tlie crt and trace tlie waveform. Tlie
 difiiculty here, of course, is trying to hold
  the p a p c ~ firmly in place and at the same
  time n i d x the tracing.
             SHORTING PROBLEMS DURING TROUBLE SHOOTING                                                     T Y P E 575 T R A N S I S T O R CURVE
                                                                                                           TRACER - PEAK-VOLTS AUTO-
    Cliucl< hliller of our Field Training group       density (tightly-notched) ceralnic strips-           TR.4SSFORlER IMPROYElIENT
calls our attention to a serious problem              see Figure 1.
t h a t can exist wlien attempting to trouble-                                                                Here is a service that if performed on
shoot an instrument incornoratinrr Iiirrli-             I f , in this trouble-shooting, the probe          the Peak-Volts autotransformer (T701 in
                                                      employed uses a large tip-the       old-style        the collector-sweep schematic) will improve
                                                      double-pinclier tip for example-the danger           its operation at low collector voltage wlien
                                                      exists of shorting out components and pos-           the H O R I Z O N T A L V O L T S / D I V con-
                                                      sibly destroying expensive transistors, di-          trol is set to the 0.01 collector-volts posi-
                                                      odes, etc.                                           tion.

                                                        A way to minimize tliis problem is to                  Prior to tliis service the P E A K V O L T S
                                                      use the ne\ver and thinner pinclier tip (Tek-        control will not turn down past around
                                                      tronix P a r t Number 013-071-see Figure 2 ) .       5 ctn of volts with the H O R I Z O N T A L
                                                      This blade-like, single-pinches tip offers a         V O L T S / D I V control in the 0.01 position.
                                                      greater margin of safety against the sliort-         a f t e r the service it will turn do\\n to 2
                                                      ing out of components in cro~vtlcd areas             cm of volts and the oneration doum to and
                                                      and the improved pincher tip has greater             up from this position will be very sn~ooth.
                                                      holding ability. The thin blade design causes           The service consists of lo~veringthe mini-
                                                      a rnininiutn of component displacement dur-          nlum voltage output of the autotransfortner,
                                                      ing trouble-shooting and facilitates cliecking       T701. T o do tliis, loosen the screw liold-
                                                      dif ficult-to-re:~li test points.                    ing the rotational limit stops and adjust
                                                                                                           tlie stops so that counter-clockwise rotation
                                                        This newer pinclier tip is designed to be          can be made tlonn to the last one or two
                                                      used with the following Tektronix probes:            windings. Care m t s t be exercised ?tot to
                                                                                                           nllow file contact to rwz o f f the end of the
                                                                                                           ecim/it~gs as damage could result.
   Figure 1. These two ceramic strips are the
                                                         P6001        P6005      P6009       P6027
same length. The conventional strip ( 0 ) con-
                        -             ..,
tains 9 notches. the hiah-densitv strio i b \ con-
tains 16 notches.
                                ,
                                                         P6002
                                                         P6003
                                                                      P6006
                                                                      P6007
                                                                                 P6017
                                                                                 P6022
                                                                                             P6028
                                                                                                           P L A S T I C L I G H T S H I E L D F O R REC-
                                                                                                           T A N G U L A R CRT's
                                                                                                             A plastic liglit sliield, similar to that
                                                                                                           used in Tektronix instruments with 5"
                                                                                                           round crt's, is available for Tektronix in-
                                                                                                           struments with 5" rectangular crt's.
                                                                                                             T h e shield is designed to block any
                                                                                                           entrance of liglit onto the phosphor via
                                                                                                           the space between the crt shield and the
                                                                                                           front panel. Light escaping through this
                                                                                                           space can prove botliersorne in some oscil-
                                                                                                           loscope photography applications.
                                                                                                             Designed specifically for the Type RM-
                                                                                                           561, the sliield is equally useful in other
                                                                                                           Tektronix instruments employing a rec-
                                                                                                           tangular glass crt-the     T ~ p e 567, Type
                                                                                                           RM567, T ~ p e527, Type R X 2 7 and the
                                                                                                           Type 561.4 110D210C or 210E. This sliield
                                                                                                           is not needed nit11 the ceramc crt since
                                                                                                           light is shielded by the ceramic envelope
                                                                                                           and rubber boot.
                                                                                                              Tektronix part numl~er of tlie ne\v liglit
                                                                                                            shield is 337-586. Order through l o u r local
Figure 2. A comparison of the older double-pincher tip          (left1 and the new thin-blade,   single-    Tektronix Field Office or l o u r Tektronix
pincher tip ( r i g h t ) . Both shown with pincher extended.                                               Field Engineer.
                                                                 (2)       6-32                        ALUMINUM SPACER
    Breakage of the 3-ivire p o ~ v e r connector
                                                                 KEPS NUTS                                                       SUB PANEL            4
                                                                                                                                                      1
o n instrunients employing a t1etach:iblc 3-                           1                                                                  I/             i
conductor power cord can occur \vlien the
i n s t r u n ~ e n t s a r e tilted o r liitcd from the
f r o n t with the p o ~ v e r cord connected.
    T h i s breakage c:m be prevented by re-
cessing tlie po\ver connector a s slio~vn in
F i g u r e 3.

   P a r t s needed :
 Qtr                    Item             Tektronix
                                          P a r t No.

   1         alu~ninutiispacer              361-012
   2         l g " , 6-32 screw             211-545
   2         6-32 Keps nut                  210-457
                                                             Fig. 3 . Pictured instructions for recessing the 3-wire connector on instruments using a detachable,
                                                             3-conductor power cord.




                                  T Y P E 527 4 S D T Y P E R X 2 7 \ \ . X \ T F O R I \ I    1IOSITOR-VOLT-IGE

                                                                             S T R E S S O S 6E\\i6 T U B E S LIURIKG T U R K - O N

      \4'1ien the Type 527 o r Type Rh4527                      I i there is no appreciable change in hook           Type RM527:
 1Vavciorm Monitor is first turned on, 1 7 3 1 1             o r tilt, V111 and V54-4 a r e prolx~hly all
 a n d 1'5% (6E\\.6 t u l m in the txvo-stage,               right and the difficulty is most likely in the           730 tlirougli 732        1066
 push-pull input amplifier) a r e subjected to               tr;~nsmittetlsignal.                                     889                      1071 tl~rougli1074
 quite a voltage stress. This stress can c:iuse                 Type 577's wit11 serial nunibers above
                                                                                                                      908                      1097
 e s c e s s i w c;~tliotle tlcterioration \vliicli, in      ill ;mtl Type RM527's with s e r i d numbers
 t u r n , Ivill cause the tube to become gassy.             :111ove 1189 li:~ve this modification installed          980                      1116
 U n d e r tliis condition the input amplifier               :it the factory. Also, the follo\\;ing serially          997                      1121
 will not perform properly and the 6E\\'6                    numbered instruments were niodiiied out                 lOz0                      1122
 t u l m in tlie input an?plifier a r e doonled              of sequence :
 t o early failure.                                                                                                  1035                      1138 through 1141
                                                                Type 2 7 :
       A siinple modification to overcome tliis                                                                      1036                      1143 through 1145
                                                                 615                          724 tlirougli 726
 prohlem consists of replacing the 0.01 @f/                                                                                                    1147 tlirougli 1159
                                                                 616                          739                    1038
 47 1i R C net\vorli in the grid circuit o i both
                                                                 674                                                 1042                      1162 tlirough 1188
  V W and 1'5.13 \vitli a 153605 diode (Teli-
  t r o n i s P a r t S u m b c r 152-141)-See   Figure
 4. A i t e r the modification, R4-40, 47 ohmthe
  parasitic resistor will connect directly from
  t h e re:ir \\.afer of the R E S P O S S E switcli
  t o pin 1 of 1:W and tlie new diode will
  connect between pin 1 and 2 of V W , Be
   s u r e the cntliotle of the diode connects to
  pin 2. Repeat these clianges in tlie grid
  circuit of V 5 l l and the tiiodification is
   complete.
        Gassy 6E\\.6 t u l m in the 1-W and 1'54-4
   positions c:iusc Iiooli and tilt in tlie dis-
   played \vnvcform. This mnlfunction is most
   :ipp:ircnt \vlien vic\vi~igthe vertical blanlct\veen the center-tap of tlie            age ~ u u s t overcome this lxicl;-l~ias hefore
                                                                                                                      1 cni or Icss.
volt:tge divider and the quiescent triotlc                 triggering c:tn occur. Tliis should not 11e
plate voltages. T h e sisty-cycle polwr-line               ;t Ii;\ntlic:\p, lio\vcver, sitice :imple trigger-
w:lveform (:ind, of course, tlie tr:lnsient)               ing voltages a r e usually nvailable in polvcr-              T o w r i i y your adjustments, connect the
is connected to the input connector.                        line testing.                                             c:dil)r:itor output to tlie External Trigger
                                                                                                                      Input coiinector. Set tlic Trigger Slope
   T h e time constant of tlic I00 p i coupling                   Scar-rios~ii:il serisitivities can he realized      Switcll to  +    E s t . You slioultl IIC able to
cxpncitor :tnd the 100I< input resistor is                 I)!. repl:iciiig the 1.50 l i ~sesistorin tlie divider     oht;iin displays siiiiilar to Figure 3 over a
short enough to effectively I~locktlie sixty-               \vitli :I 2 2 0 1 ~resistor. It \\.ill I)e iicccss:iry    raiige of input voltnges i r o ~ i i2 to 10 volts.
cycle co~iipoinent; \vliile :it the same time,              to check the 11l:ite vo1t:iges for iniInl:mce.
alloning fast-c11:mging tr:uisient volt;tges t o              Removing tlie ground {I-om tile I-iglit-1i:uid             I M n i l s on ho\v this modiiic:ition tiiigl~t
pass through t o the input gritl. T h e t\vo                   triotle grid \vill per~iiit using tlle TIITG-          he i~istalletl in :in oscilloscope :me k i t to
triodes :\re operating as a pnr:ipliasc in-                    G E I I I S G I , I ~ \ T L control to achieve per-    tlie inventiveness of tlic re:itler. Certainly,
verter. If tlic input trmsieiit is positive-                   fect 11:tl;ince. Of course, the opcrntor must          consitler;ition should be given to ho\v fre-
going, it \vill cause tlic left-l1:ind plate                   Ile careful not to tlisturh this control once          quently it ~iiiglitbe used. In those situations
voltage to go tlo~vn. Similarly, if the input                  :itljusted.                                            \vInerc this tiiotle o i operation \vould be
transient is 11cg:ttive-going, it \\.ill c : m e the                                                                  used often, :i permanent s\vitcli function
riglit-1i:uitl plate to go down.                              T o :idjust the circuits i o r correct oper-            \voultl seem most convenient. On tlie other
                                                           :ition, set t l ~ e iront-p:mel coiitrols ns lol-          li:uid, for occasion:il "one-shot" applications,
    A negative-going voltage on either triode              1on.s :                                                    it might he simpler to "tncli-in" tlie conipo-
 plate will c:iuse the associated diode to go                                                                         ncnts :is needetl. On tlnose instru~iicnts1i:iv-
 into contlt~ctiun. \ \ l ~ e n one of the diodes                                                                      ing zun operator's manual conip:~rtment in
 conducts, a neg:itive-going volt:ige :~ppcars                                                                        the riglit-



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