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USEFUL INFORMATION FOR USERS OF TEKTRONIX INSTRUMENTS
NUMBER I Z PRINTED IN U.5.A FEBRUARY 1962
MEASURING A SMALL AC trol the dc voltage to I N I ' U T B. See Fig- I n using the Type Z Unit t o measure
COMPONENT ure 2. T h e capacitor, potentiometer and the signals discussed in this article, set the
RIDING ON A DC VOLTAGE leads to the oscilloscope of this circuit, as 4 C - D C switch to DC. Set the M O D E
well a s the lead from the voltage under switch to A-Vc if the signal is applied to
investigation to the oscilloscope, must he I N P U T A o r to Vc-B if the signal is
If you wish to measure a stnall ac com- adequately shielded against stray hum pick- ~ppliedto I N P U T B. Set the C O M P A R I -
ponent riding on a tic voltage, a number up. A battery offers certain advantages S O X - V O L T A G E P O L A R I T Y selector to
of ways t o do so present tl~emselves. T h e over an ac power supply, i.e. low noise and natc11 the polarity of the dc component
following describes several of the more no ripple. F o r signals having a negative tlc sf the input signal and set the C O M P A R I -
simple methods employing Tektronix oscil- component reverse the battery connections. S O N - V O L T A G E R A N G E selector to a
loscopes. voltage value that exceeds the voltage of
P e r h a p s the most simple method is to INPUT [he d c component of the input signal By
switch tlie input selector o r AC-DC switch 1- w i t h ac comoonent
A means of the Heilidial, adjust the compari-
of the scope's vertical input to the A C posi- son voltage to cancel out the unwanted dc
tion. D o i n g this switches a dc blocking m e t o - a x i a l cable component of the applied signal. \Irith the
capacitor into the circuit between the input A - I N P U T VOLTS/CM (ATTENUA-
terminal and the vertical amplifier. See T O R ) control in the .05 position, a 5 rnilli-
Figure 1. T h e capacitor blocks the dc volt- volt ac component will give 1 lnrn of
age but allows the ac component to pass deflection on the crt screen. Maximum
through t o the amplifier. This blocking o r voltage swing a t this sensitivity is .t- 100
ac-coupling capacitor is usually a 0.1 pfd volts combined ac-dc signal.
capacitor rated a t 600 volts and the input- By using the V O L T S / C M ( A T T E N U -
grid resistor a 1 megohm precision resistor. A T O R ) control, mixed ac-dc signals up
T h e r c time constant of this combination to a n~axirnum of 500 volts peak-to-peak
is 0.1 second which contributes 3-db attenua- Figure 2 can be investigated in this manner. Bear in
tion f o r 2 cps (approximately) sine wave This method will work satisfactorily for mind, however, that the sensitivity of the
signals. Combined ac and dc voltage of the dc components up to 2-5 volts depending osc~lloscope will be reduced by the factor
input signal should not exceed 600 volts. on the instrument used; beyond that you to which the V O L T S / C M control is set.
may saturate the input stage of the dif- * .% Type 81 Adapter is required f o r use
ferential amplifier unless the input is at- with Types 581 and 585.
tenuated.
F o r dc components up to 20-50 volts, a
pair of 1 0 s probes (one for each input) CONSTRUCTIVELY CRITICAL
plus 45 volts from batteries will \vork satis- COMMENTS O N
factorily. This will, however, reduce the "GRATICULE MOUNTING PROBLEMS"
sensitivity of the oscilloscope by a factor
of ten. Tektronix Field Engineer Bob L e Rrun
In the case of the Type G Plug-In P r e - ( I h l t i m o r e ) writes us regarding the article
amplifier which has separate input-attenu- "Graticule Mounting Problems," lvhic11 ap-
T h i s method works well provided the ator controls for each input, you do not peared in the December '61 issue of
above conditions a r e met and the frequency need 1 0 S probes. Using these attenuators, S E R V I C E S C O P E , as follows:
of the a c component is above 10 cps. T h e a 1.5-volt battery is sufficient for balancing "There a r e a couple of statements in this
vertical-sensitivity control can he set t o out a tlc component u p to 600 volts, though article that I'd like to comment about.
maximum if needed. the display sensitivity under these extreme
S o ~ v let's make the conditions a little Statement: 'There is little to he gained
conditions is only 20 v/cn~.
tougher. \\'e Imve a few millivolts of lo!\- by placing the light filter
T h e Tektronix Type Z Differential C o n -
frequency component riding on a dc voltage over the graticule. T h e grati-
parator C n i t in a Tektronix Type 530,
of about +2 volts. T h e frequency of the cule lines will not sho\v
Type 540, Type 550, o r Type 5SO* Series
;ic component is tlo~vn beloxv several cycles through the filter sufficiently
Oscilloscope, will eliminate the need for tlie
per second. Here a differential input ( s u c l ~ enough to be useable.'
extraneous circuitry shown in Figure 2.
a s that available on the Tektronix Type This versatile unit contains a built-in reg- Comment : Placing the light filter over
502 o r T y p e 503 Oscilloscope, o r the Type ulated dc comparison vo1t:ige. \\'hen the the graticule reduces parallax
63 o r T y p e D o r Type G Plug-In P r e - M O D E switch is in the A-Vc o r Vc-R by moving the graticule and
:unplifier in a Telitronix Oscilloscope for position, the calibrated dc voltage is inter- trace one filter thickness
\vhich the preamplifier is designed) ivill d l y applied to cancel out any unwanted closer together. T h e gr;lticule
help t o solve the problem. Set the input- dc component in the applied signal. This lines can I)e made to sl~o\v
selector s\vitch to .+R, and the AC-DC allows accurate measurements of relatively tllrougl~ enough to he useahle
switch to DC. Apply the signal to I S P Y l ' small ac signals riding on relatively large tlc under most ambient light con-
X and feed an equal tic voltage to I N P C T signals. Precisely accurate selection of plus ditions hy using the white
B. A n inexpensive multi-turn potentiometer o r minus dc comparison voltages over a g r a t i c d e lines. T h e rcti lines.
(such a s rnade by the Chicago Telephone range of from 1 to 160 volts is possible 1,: of course, ivon't sllo\v through
Sup1)ly Company), a battery and a bypass means of a C O M P X R I S O S - \ - O L T A G E :I colored filter unless it too
capacitor provide a convenient way t o con- R - \ S G E selector and a Heilidial control. is red.
S t a t e m e n t : 'If you use the Tektronis Tlie modification kit includes a complete ;~lx-see picture above. .Apl,arently tlie
Bezel, T e k number 014-001, set of components, pravired amplifier as- ahel has been applied upside down. The
( f o r mounting cameras, other ;embly, parts list, schematic, photos and irrolv supposctlly pointing to tlie positive
than Tektronix types, 011 step-by-step instructions. -4 skilled tech- :nd of tlie Ixlttery ;ictually points to tllc
Tektronix 5" oscilloscopes). nician can install the modification in ap- 1eg:itive end.
it takes the place of the proximately four Ilours. R;ttteries of this configuration and voltage
graticule cover in the above Order through your local Tektronis Field ire used in tlic Tcktronis Type 321 Tr;in-
instructions.' Engineer. Specify Type 551 Chopping- ;istorized Oscilloscope. An esperienced a~itl
Trmsient Blanking Field Mod Kit, Tek :areful operator \vould proba1)ly notice this
Comment: T h e T e k Bezel ( f o r non- S o . 040-274. Price is $17.50. :rror in labeling and install the battery prop-
T e k cameras) can be used * Other Tektronis Oscilloscopes in \vhicll ~ l polarized.
y
wit11 the graticule cover and tliese Plug-In Preamplifiers will pro- I t is not inconceivable, l1on.ever, that the
I believe sl~ould be because duce transients a r e : n t t e r y might be installed incorrectly (polar-
without it light leakage ruins ( 1 ) . Type 531, Type 535, Type 541, Type ty re\.ersetl) by a n inexperienced operator
pictures." 545, serial numbers 101 to 3999. >r one in ;I hurry. I n :in instrument oper-
Rob's comments a r e good antl u-e appreci- F o r these instruments ask you. Tek- tted under these conditions the incorrectly
a t e them. T h e idea of using the white tronis Field Engineer for Chopping- ,nstnlletl battery \vonltl eventually esplotlc.
g r a t i c ~ l l e lines never occurred to this Transient Blanking Field Mod Kit, The csplosion could have sufficient force to
e d i t o r - just too simple a solution, I guess. Tek S o . 010-200. Price is $5.23. ierior~slydamage the oscilloscope.
B o b is also correct in his belief that the ( 7 ) . Type 531.4, Type 535.4, Type 541.4, For the benefit of those who may not
graticule c o \ w should be used with the T e k Type 545.4, serial numbers 5,000 to Iknolv, in this type of niclcel-cadiurn Ixittery
Bezel ( f o r non-Tek cameras). \\-it11 the 20,000. F o r these instruments ask tlie protruding o r nipple-like enti is c ~ h l c ~ j s
your Tektronis Field Engineer for .he positive end. If there is any question
graticule nuts removed, the bezel will mount
Chopping-Transients Blanking Field thout the polarity of a battery, check it out
o n the graticule studs and right over the
Mod Kit, Tek S o . 040-198. Price ivitli L voltmeter.
:
graticule cover. Reinstalling the graticule
is $5.25. Every nickel-catlium battery received :1t
n u t s will then hold all firmly in place
Tektronis from our suppliers is placed on n
T Y P E 502 S \ \ X E P L O C K O C T M O D charging line. I t ~ v o u l d be virtually im-
KIT possible f o r :In incorrectly marked battery
A CLARIFICATION F o r Type 502 Oscilloscopes, all serial L get into a production instrument o r to
o
I>e shipped on ;I customers parts order.
numbers.
I n the December issue of S E R I - I C E However, this brand of battery is nation-
This field modification kit converts your
S C O P E , tlie article "Accurate Frec1uenc~- ally marketed antl m : ~ ybe purchased lo call^^.
Type 502 Oscilloscope for the study of one-
Measurements" suggested a method for \\.e do, therefore, urgently recommend a
shot pl~enomena. c a r e f d inslmtion of locally purchased bat-
checking tlie accuracy of rt Tektronis Type The mod kit contains a xvired chassis as-
180A Time-Mark Generator by beating teries of this type before installation in zn
sembly, new front panel, and necessary com- instrument.
t h e 1 psec markers against the \\'\\'I7 car- ponents to incorporate the s\veep-lockout
rier. The statement that the "difference feature in your instrument. I t also includes
frequency in cycles ~ v i l lbe a measure of the a photo, schematic, parts list and step-by-
time-mark generator's accuracy in parts per step instructions.
million" may be misunderstood. Order tlirobgh your T e k t i o n i s Field E n -
T h e actual beat (difference) irequeucy MISSING INSTRUMENTS
gineer. Specify Type 502 S ~ v e e p Lockout
will be between a I~nr~ironic tlie 1 psec
of Mod Kit, Tek. KO. 010-209. Price is $45.00.
( 1 mc) 180.4 output and the particular T h e National Broadcasting Company in
\\:\\'V carrier used. If \\'\\.Y1s 5 rnc car- Burbank, California, ,reports that a Tek-
rier is used, a beat frequency of 5 cps will tronis Type 310 Oscilloscope, s / n 1864 dis-
indicate a 180A error of 1 ppm. If the A WORD OF CAUTION appeared from their premises on August 8tl1,
10 nlc \ \ l \ ' V carrier is used, a beat fre- 1961. They presume the instrument to be
quency of 10 cps will indicate 1 ppm error stolen since a check of authorized personnel
in the 180A, and so forth. failed to reveal the instrument. If you have
T h e nominal accuracy of the 180A xvben any knowledge of the whereabouts of this
shipped from the factory is +.001%, o r oscilloscope, please contact Mr. F r a n k Som-
10 ppm. After being zero-beat wit11 \\.\\'I7, mers, Engineering Department, National
it will remain accurate within f3 parts Broadcasting Company, 3000 Alameda, Bur-
per million over a 24 hour period. Innk, California.
A Tektronix T y p e 317 Oscilloscope, s / n
001771 is missing from the U.S. A i r Force
at Selfridge A F B , Michigan. Tlie A i r Force
FIELD MODIFICATION KITS non~enclatureof the missing property is as
follows : Portable oscilloscope, Model #317,
T Y P E 551 C H O P P I N G - T R A S S I E K T Serial #001771, Stock #676-1302, Class
BLANKING FIELD M O D K I T Symbol 6625, Listed value : $800.00
F o r Type 551 Oscilloscopes, all serial If you have any knowledge of this instru-
numbers. The Type 53C, Type 53/53C and ment contact Gene P . Moritz, Colonel,
T y p e C-A Plug-In Preamplifiers will pro- U S A F District Comm;uider, 507th O S I De-
duce troublesome transients in a Type 551 tachment, Selfridge A F B , Michigan.
Dual-Ream Oscilloscope \vhen operated ~vitli
t h e preamplifier M O D E switch in the T h e Picatinny Arsenal a t Dover, New
C H O P P E D position.* Jersey, reports that a Tekronix Type 517
Ii'e have available a field modification Oscilloscope is missing f r o m their premises
kit that provides a circuit to blank the and is thought t o be stolen.
transients generated under these conditions. If you have any information on the where-
T h i s kit provides individual C R T cathode- abouts of this instrument, please contact the
selector switches that allow blanking on Picatinny Arsenal o r the Tektronix Field
either or both the LO\\'ER and V P P E R Recently \ve came across a 1.25-v nickel- Office, 400 Chestnut Street, Union, New
beams. cadium battery lvith an improperly applied Jersey.
Copyright 1962 Tektronix, Inc.
reports t h a t a Tektronix Type 317 0 s c 1 l l ~ - 131138' Sanford Ave
scope, serial number 879, mas lost In translt Flushing, S e w York
t o one of their R a ~ Flaw Detection Cars.
l
Information on the whereabouts of this i TI pe 545 o r Chas. \\'ikon
instrument should be sent to Mr. E I TI pe 545.4 501 Keebler Road
Cook, Maintenance Manager, Howe P r e - King of Pruss~;t, I'a
cision P r o d u c t s Company, Shelter Rock
Road, Danbury, Connecticut, Telephone. I 3" Tektronis D . Cleveland
PIoneer 8-9243. Oscilloscope 10 Museunl Road,
Beverly, M;iss.
USED INSTRUMENTS FOR SALE INSTRUMENTS TO TRADE
1 Type 561, s / n Tr:tnsitel Internation- I T) pe 515.4 wope Bart I-Iealy
for T I Technical Instru
889. P r i c e :%I Corporation
scope ments, Inc.
$382.50 615 \\.inters .Avenue
1 Type 72 Plug- P:tr:mus, S e w .Terse>. 90 Main Street
In, s / n 565. Reading, Mass
Price $225.00
1 Type 67 Plug- KING SIZE HELMHOLTZ COILS
In, s / n 1031. USED FOR TEST AND RESEARCH
Price $135.00
Figure 2
1 Type 541, s / n Bernie Stapler Tel 378 Columl~ia Tec1inic:d turing Staff Engineers) recently completed the same magnetic field with the sweep
Corporation construction of a king size Ilelniholtz coil. synchronized to 60 cycle ac antl no signal
24-30 Queens Rroo1;- ( A He11i1lioltz coil consists of t\vo equ;tl- applied to the scope input. Kotice that in
Iyn Express, \\'est diameter coils spaced a distance equal to this 25 Oersted magnetic field the trace on
\Voodside 77, S e w their diameter apart.) They will use the the face of the crt shows only ahout 2 mm
York. coil to measure the effects of magnetic of ripple. This indicates that the crt shield-
Phone : YElloastone fields on Tektronix oscilloscopes. ing prevents all hut % negligible amount of
:
2-0800 This Helmholtz coil contains two coils, the magnetic field from reaching and
each two meters in tlianlcter and holding influencing the electron heam of the crt.
1 T > p e 316, I.tte August Sclionefeltl 90 turns of heavy copper wire per coil. .A Although built primarily to answer the
niodel I'rec~s~on In5trument total of just under 4,000 feet of \vim - question, "Can \ye put our oscilloscopes in
Co 40 pounds of copper. Spacing tlie coils a magnetic field 5 units (Oersteds) strong
1011 Commerctal S t one meter apart and applying an electric and not displace the crt spot more than
San Carlos, C a l ~ f current sets up n highly uniforni magnetic 1/16th of an inch?", the Heln~lloltzcoil will
field of a l ~ o u ta cubic meter in size bct\veen lend itself to many other uses as a test ant1
1 T y p e N Plug- Morris-Cooper Corp. them. TIi:%t leaves plenty of room to insert research tool.
In, s / n 683 3832 Terrace Street an oscilloscope in the field and ol~seryetlie \VIiat's the ans\ver to the question? \\'ell,
1 Type 110 Pulse Philadelphia 28, P a . efiect it produces on the elcctron 11e:tm of TMSE's best guess from previous work \vas
Generator antl Phone: I\' 6-6533 the scope's crt. that we could - but no one \vas positive.
Trigger Take- Xo\v we k n o w we can.
o f f , s / n 291
1 Type 113 Delay
Cable, s / n 291 TRUANT SCOPES RETURN
1 Type 514AD Engineering Xssoci- TO SCHOOL
ates T w o oscilloscopes absent without leave
434 Patterson Roatl f r o m their respective' schools returned t o
Dayton 19, Ohio the halls of learning recently. M r . R . W .
Moulton, Executive Officer of the Univer-
2 Type 551 scopes I*. Nucci sity of \\'ashington Chetnical Engineering
2 Type C.4 Plug- General Applied Sci- Department, writes us that the Tektronix
I n Preamplifiers ence 1~l1or:ttories Type 504 Oscilloscope, serial number 214,
Merrick Sr Stelvart reported missing in the December '61 issue
Avenues of this paper, mysteriously reappeared in
\\'estl>ury, Long Is- one of their laboratories.
land, New York Through our Palo Alto Field Office,
we hear that the Tektronix Type 515A
1 T y p e 535, R S Kampf, P A Oscilloscope, serial number 6135, (also re-
\/n 10751 Computer D ~ v ~ s ~ o n ported missing in the December '61 issue
3 'Type 51.5, Pliilco C o ~ p o r a t ~ o n of SERVICI.1. S C O P E ) has been returned
\/n 11669, 13900 \\'elih Road to the S a n Fr:uicisco City College after a
11670. four n~ontlis:ihsence.
13671 \\'e have no \vay o i knowing if the notices
8 'Type 541, \\'~llo\\ Groxe, P a . Figure 1 in the "Llissing Instrun~cnts" column of
\/n 7171, P l i o n e Oldiieltl 9-7700 S E R V I C E S C O P E played any part in the
Figure 1 sl~o\vs :i Tektronis T ~ y e 531.3 return of these instrun~entsto the schools.
7172,7473, ~ s c i l l o s c o p e sitting in the magnetic fielc
7190, 7191, \\'eld like t o speculate, however, that maybe
wit11 a search coil (tlie \v:tnd-like tlevic' -just mayhe-the borrowers o r "kidnap-
7192, 7193, laying on top of the scope) connected 1,
7194 pers" of these instruments read the notices
the scope input. T h e trace on the crt f:~c in S E R V I C E S C O P E and that either pru-
indicates ;I pickup 11y tlie se:~rcli coil o dence o r an uneasy conscience moved them
an nc mnp~ictic field that iiieasures 2. to return the oscilloscopes.
USED INSTRUMENTS WANTED
Oersteds peak-to-peak. \\:hatever the cause, the scopes were re-
1 T y p e -502 Luis A. Roclia, % Figure 2 slio\vs the same oscilloscope i~ turned atid that's the important thing.
A LIMITED OFFER me flange, equ~distant f r o m each end anti
In 5" centers, vie drilled and tapped t\vo
\\re have remaining :I small quantity of ioles. \Ve usetl a number 36 drill and a
the hooklet entitled "Impulse Tests :untl 5-32 tap. Into these holes u.e screwed the
Measuring Errors". \\'e can best descrilx .wo banana plugs that attach the holder to
the ~ n a t e r i a l in this hooklet hy quoting the In oscilloscope by fitting into the two top
introductory p;iragrapli : zraticule studs. O n the top surface of the
"It has been sliov,m . . . . in internatioml tiolder, we laid out and drilled and tapped
comparisons of the work of various 1al)or;t- ziglit equi-distant holes again using a num-
tories, that the accuracy of measurement in ber 36 drill and a 6-32 tap. Into each hole,
tests with impulse voltage does not fulfill we screwed a 6-32 x .1/8" binder head screlv.
t h e d e n ~ a n d sit has been thought appropriate Taking a 1%" length o r aluminum rod, we
t o nlake. This article analyses a part of drilled and tapped it at each end for a 6-32
t h e question - the problem of measuring screw. W e then mounted the rod on one
he amplitutle and s l ~ a p eof impulse voltages of the installed 6-32 x .?/s" screws. I n the
Figure 1 exposed end of the rod, w e installed a 6-32
a n d currents with sufficient accuracy for
practical purposes. T h e methods of check- stud. W e made the stud by running a 6-32
ing impulse circuits which have been usetl nut onto a 6-32 x 5/8" screw, threading the
T h e design of the pictured holder permits screw into the rod until it bottomed and
a t t h e High-Voltage Laboratory at L u d v i l a
attachment of it t o a n y Tektronix 5" oscil- then turning the nut down snug against the
f o r some years a r e descril~etiand the mini- loscope (see Figure 2 ) except when an oscil-
mum detnands which should be m:lde on rod. \\'e then cut the screw off with a
loscope camera is in use. hack saw so that about extended he-
measuring circuits intended for various
impulse tests are set out. Descriptions a r e yond the nut. After rounding off the edges
given of a number of measuring circuits". of the stud, we ran the nut off the stud.
\\'e o f f e r these booklets to those readers This reforms ;und deburs a n y daniagetl
of S E R V I C E S C O P E whose interests lie threads on the stud.
in this area. Place your requests for a copy U s e the rod and stud to hold the pincher
with your local Tektronix Field Engineer. tip of the prohe and the other seven screlvs
\\'e must of necessity refer all requests to hold tlie other probe tips.
sent direct to us to our Field Engineer \Ve used a rat-tail file to remove the
serving the area in which the request metal f r o m the circular cut out of our
holder.
originated. So, since this o f f e r is on :I
first-come-first-served basis, you will espe- -
F o r attachinp the * nrobe holder (that white
plastic object with a slot) to the prohe-tip
dite your request if you place it with !-our
holder, we used an ordinary ground post
local Tektronix Field Engineer.
mounted in a hole drilled in the front flange
of tlie probe-tip Iioltler.
Perhaps you do not care to mount your
probe-tip holder on the graticule studs of an
A CONVENIENT PROBE-TIP HOLDER oscilloscope o r to construct as functional a
Figure 2
holder a s the one described here. By apply-
Tektronix Field Engineer Jerry K r a s - T h e circular cut out in the base o i the ing the idea of tlie seven screws and the rod
berger sent in this idea for a convenient holder allo\vs it to fit over the new Polar- with stud, ~ O L Ican make a probe-tip holder
probe-tip holder. ized Viewer (see October '61 issue of SEII- to suit your individual ambition and neecis.
I f you, as this writer often does, spend V I C E S C O P E ) o r a tubular light shield. Install it any place that's handy-bench, wall,
frustrating m n u t e s looking for mislaid probe F o r the base of this holtler, \ye usetl a oscilloscope cart.
tips, the do-it-yourself probe-tip holtler pic- piece of sheet aluminum 2" wide by 6" long. Installed and used, this probe-tip holder
tured in Figure 1 will undoubtedly appeal W e formed the %" flanges by making two should save you time and put an end to your
to you. 90" bends using a sheet metal bre:tk. O n probe-tip hunting.
T e k t r o n i x I n s t r u m e n t - R e p a i r Facilities: T h e r e is a fully-equipped a n d properly-staffed T e k t r o n i x I n -
s t r u m e n t R e p a i r S t a t i o n n e a r you. A s k y o u r Field E n g i n e e r a b o u t T e k t r o n i x Instrurnent-Repair facilities. 2/62
USEFUL INFORMATION FOR USERS OF TEKTRONIX INSTRUMENTS
NUMBER 1 3 P R I N T E D I N U.S.A APRIL 1962
FAN-VIBRATION PROBLEMS: -un the motor. If the fan motor is the culp- lent to show the filament V734 connected
SOME CAUSES AND CURES .it, vibration will still be present but, most o the elevated ( i- 350 v) f ilatnent supply.
ikely, considerably reduced. This will in-
licate that the fan motor, through wear, has
In Tektronix instruments employing leveloped excessive bearing play. More r Y P E 535A, T Y P E 545A, T Y P E RM35A,
forced-air ventilation, fan vibration is not -arely, it may indicate :I defective motor 9 N D T Y P E RM54A O S C I L L O S C O P E S
normally a problem. Fan-vibration problems, In either case, the motor should be re- When operating the above instruments
when they do occur, generally stem from one placed. intl using Time Base B triggered in the DC
of two sources-the fan motor or the fan- Absence of vibration will indicate that node, tube V94 map go into oscillation. The
blade assembly (fins, spider and hub). the fan-blade assembly is too badly out of )roblem can he overcome by tube selection.
In most of our forced-air-ventilation in- digntnent to be corrected by the means qowever, a very simple tnodification will
struments, the fan motors operate at rela- lescr~hed here. Under these circumstanceq cive a more satisfactory solution and elimin-
tively slow speeds. T h e fan motors used in you will no doubt find it most expedient to lte the necessity to select tubes.
these instruments are typically in proper replace the old fan-blade assembly with a T o make the modification, locate R90.
balance a s we receive them from the sup- new one i 1.2 meg, 1 w, 10% resistor. You will find
pliers. I n instruments where the rotation -his resistor connected between the 4th and
speed of the fan motor might conceivably 3th notches (counting from the front of
cause a problem we shock mount the fan :he oscilloscope) of the ceramic strip located
motor a s a precautionary measure. SERVICE HINTS llmost directly over tubes V74 and V95.
The fan-blade assemblies are fabricated These tubes are in turn located on the
by techniques designed to produce assern- T Y P E 551 D U A L - B E A M OSCILLO- swing-out chassis containing the Time-Base
blies in balance both statically and dynami- SCOPES R Trigger and Generator, Delay Pickoff,
cally. T h e fins in a properly balanced assem- Filament wiring change to increase power and External Horizontal Amplifier circuitry.
bly a r e all aligned to operate in the same supply reliability-s/nls 101 to 2357. Replace this resistor with a 2.2meg, % w,
plane and all have the same pitch or angle You can considerably reduce the possi- 10% resistor. Correct the instruction man-
relat~veto the axis of the fan-motor shaft bility of heater-cathode breakdown in V734 ual (Time-Base B diagram) to show the
Troublesome fan vibration is niost often
caused by an unbalanced fan-blade assembly
(6AU6 error-amplifier tube in * 500 v new value for R90.
This modification applies to instruments
power supply regulator) by changing the
Instruments undergo a check, before they heater of this tube from a grounded supply with serial numhers below the following :
leave o u r factory, to assure that they have to an elevated supply. Type 551 'scopes, Instrument Serial Number
a mininiu~n fan vibration.
of serial numbers 2358 and up incorporate Type 535A 27860
However, any rough handling of the in- this modification. Type RM35A 2550
strument can upset the balance of the fan- T o modify instruments in the field, re- Type 545A 33015
blade assembly by altering either the pitch move the bare wires connecting the fila- Type RM45A 2760
or rotation plane (or both) of one or more ments of V734 (pins 3 and 4) to pin 7 Respective instruments hearing serial nuni-
of the fins (grounded) of V657 and the 6.3 v filament hers above those listed here have this modif-
Often you can restore the fms to t h e ~ r buss at pin 8 of V687. ication incorporated at the factory.
proper plane antl degree of angle by the Also, unsoltler from pin 4 of V734, the
following procedure : hare wire coming from pin 9 of V616 and T Y P E S (53/54) A, B. C-A, G, A N D H
1. Check all fins to make sure they turn resolder it to pin 1 (grounded) of V619. PLUG-IN PREAMPLIFIERS-TRANS-
in the same plane by referencing a Wire the filaments of V734, in parallel C O N D U C T A N C E A N D G A I N CHECK.
gauge bar (screw driver tip, pencil with those of V747. For proper access, you I t is sometimes difficult to determine in
or etc.) within of one of the side will probably find it necessary to unsolder a low-level, low-gain, video amplifier stage,
edges of the fins. While maintaining one or two of the components mounted whether transconductance and gain are ade-
a slight axial pressure toward the fan above the V747 socket. Unsolder these quate or whether the tuhes should he re-
motor, slowly rotate the fan-blade components at one end only and bend them placed.
assembly and note the clearance be- up out of the way. If you find it necessary Here's a trick that works well in Telc-
tween the gauge bar and the fin edges. to remove the P T M capacitor C744 (0.01 tronix Plug-In Preamplifiers Types (53/
If the fins are all turning in the same p f ) , unsolder it at both ends and tempo- 54) A, B, and C-A for checking the in-cir-
plzne, the clearance will be the same rarily remove it. cuit transconductance of the input-amplifier
f o r each fin. Correct any difference Use insulated or sleeved wire to connect stages, and in Types G and H for check-
by grasping the tip of the offending pin 4 of V734 to pin 4 of V747. If you pay ing the output-amplifier stage, using a dis-
fin between x thumb and forefinger careful attention to lead dress, you may use play of the calibrator waveform or other
and bending in the required direction. bare wire when connecting pin 3 of V734 convenient signal.
2. Con1p:ire the pitch of a11 fins by check- to pin 3 of V747. The trick is si~nplyto rotate the VAR-
ing both sides of the fin cdges as ill After carefully checking the wiring antl I A R L E V O L T S K M control over its full
step 1. Twist antl hentl the fins with lead dress, replace and resolder any compo- range with the G A I N ADJ control fully
thunib antl forefinger as necessary tc nents unsoldered for access. clockwise. If the range of the variable
m:tke each side of each fin run ir A resist:ince check should now show: Pin vol ts/cm ch;mges display ;implitrlde by 2%-
its proper plane. Correctly done, tlii: 3 or 4, V734 to k 3 5 0 v supply buss, approxi- to-1 or more, the transcontluctance of the
should establish the s:me degree of ~nately 100 k. Pin 3 or 4, V734 to ground, tuhes in the affected stage is adequate. Tf
pitch for each fin. 110 I< or more. the control range is less than 2%-to-1, the
If vibration still persists, remove the fan- Correct the instruction tn;\nual (.power tuhes are prohahly weak and should hc
1)latlc assembly from the motor shaft an( supply diagr;un) for the modificd ~ n s t r u - chnngctl.
T h i s method will also work with the Type mperative. Tektronix part numbers for
K a n d L Plug-Ins( input amplifier check). hese tubes :
I n these instruments, however, the range of (154-187) tube, electron Type 6DJ8 $2.75
the variable volts/cm change in the display (154-195) tube, electron Type 6922 $7.35
amplitude will be 2-to-1 (2%-to-1 with new
360