Ballantine 305A User manual

INSTRUCTION BOOK
for
MODEL 305A PEAK RESPONDING
ELECTRONIC VOLTMETER
BALLANTINE LABORATORIES, INC.
BOONTON, NEW JERSEY

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MODEl 30SA
INSTRUCTION BOOK CONTENTS
FOR
MODEl 30SA PEAK RESPONDING ELECTRONIC VOLTMETER
Pa ge
1. INTRODUCTION
AND DESCRIPTION 3
1.1
Purpo se and Use 3
1.2
Techni cal Characreristics 3
2. OPERATION . 3
2.1
Power Connecrion
3
2.2 Starting Procedure
3
2.3
Function of Swit ches 4
2.4
Me asu rement of Peak-to-Peak Amplitude s . 4
2.5
Measurement of Pe ak Amplitudes
..j
2.6 AC Overloa d Considetati ons 4
2.7
DC Component of Input Si gnal
5
2.8
Input Impedan ce 5
2.9 Use as an
Amplifiet
5
2.10 Pan el Controls with Screw Adjustment
5
2.11 Use of Adjustable Controls
5
2. 12 Peak Me as urem ents Below 1 Millivolt . G
2.13
Measurin g Short Pulses with low Dut y Cycles 6
2. 14 Te c hniques for Highe r Accuracy Me asurem ent s . . 6
2.1 5 Use as an
Ammeter
6
2.16
Me as urin g Ab ove 1000 Volts Peak 7
217
Power line Effects 7
2.18 Effect of R.
F. Line Transient s.
7
3. CIRCUIT DESCRIPTION 7
3 1
Input Attenu;!ror 7
32 Input Amplifier 7
3.3
Buffer Stage an d Midsection ArrenuatOr ..
7
3.4
Output Amplifier
7
3.5 Peak-to-
Peak Dete ctOr.
7
3. 6 Pulse Stret c her 8
3 7
Me as uring Stage . 8
38
Power Supply S
4. MAINTENANCE
8
4.1
Gen eral S
4.2
Recommended Maintenanc e Pro ced ure 8
4. 3 Necessary Ma
inten ance Equipment 8
4.4 Removal
of th e Case 8
4.5
The 200 Hour Check 9
4.6
The 1000 H ou r Check 9
4.7
The 2000 Hour Check . 9
S. SERVICE
AND TROUBLE SHOOTING
10
5 .1
Gener al
10
5. 2 Necessary
Equip ment
10
5.3
Simple Service Pro blems
10
5.4
DC Volt age Checks 10
5.5
Signal Tracing ... . . . . .. .. . .
11
5.6 Amplifier Frequc:ncy Response
Adj us tment
12
5.7 A[[
cn u3 ror Frequ en cy Response
12
5.8
Replac em ent of AttenliatOr ResistOrs 12
5.9 ServiCing the
Pow er Supply
13
5.10
Tr ouble ShoOting Chart . 14

FUSE
lA SLO-BLOW
PILOT LIGHT
POWER
SWITCH
INPUT
TERMINALS
RANGE
SElECTOR
Fig. 1
Ballantine Model 305A
Peak Responding Electronic Voltmeter
®
----====-=-=::-:-::=---:---:--:::- - - -
® 0
,('
Model 305A-S/2, Rack Panel Mounted Version

MODEL 305A
1. INTRODUCTION AND DESCRIPTION
1.1 Purpose and Use
The Ballantine Model 305A Peak Responding Electronic
Voltmeter is an amplifier-de
te cror type insrrument provided
with a peak dete
nor circuit for peak-ro-peak or pe ak va lue
measurements.
The insrrument indicares peak-ro-peak or
peak ampl
ir ud es of reperiri ve waveforms including si ne,
square, triangular and complex
wa ves, and pulse rrains.
The measurement is indi
ca teu on eirher of rwo loga rirhmic
volrage sca
les w hi ch allow rile same hi gh accuracy at alJ
points. A rhird linear decibel sca le with a range of 10
decibels
is al so provided.
T
he sens iri ve and srable wide-band ampli fi ers associat eu
wirh a special peak derecror c ir cu ir exte nu rhe sensirivity
of
th e insrru ment inro rhe microvolr region This a lJ ows
rhe measurement of low energy pulse rrains wirh pul
se
wi drhs down ro 0.5 microsecond anu repetition rares as low
as 5 pps.
In audirion
ro ir s function as a vo lrmerer, the 305A may be
used as a wide-banu, fast rise-rime ampl ifi er.
T he instrument design proviu es a ll (o ntr ols and 'lJjusrments
on the front panel.
The Model 305A ma y be obrain cd in
portable and ra ck-mo unttu versio ns.
1.2 Technical Characteristics
Voltage Range
1 millivolr ro 1000 vol rs peak·ro-peak or pe ak in 12 rang es .
Frequency Range
5 ro 500,000 cps. S in e wave - 200 ro 300,000 cps. square
wave. Pulse
Range
Dur a ti on - 0.5 ro 2, 500 microseconus. Reperi ti on ratc -
minimum 5 pps. Accuracy
Sine Wave- := 2 ': (:
20 cps. ro 200 kc.
z:4':i; 5 cps.
ro 500 kc.
Square Wa ve - -= 31 ;· (: 200 cps. to 300 kc.
Pulses - _ 3 S:-& above 3 microseconds and 100 pps.
- 59c above 1 microsecond and 100 pps
± 5 ~ c below 1 microsecond and tOO pps when
correcrion is used.
-5':" below 3 milli vo lr s for all waveforms.
Input Impedance
2 megohms shunt ed by 10 pF on 350 millivolt range anJ
above. 2 megohms and 25 pF below 350 mi ll ivo lt ran ge
Meter Scales
Lo garirhmic vo lr age sc ales fr om 0. 9 ro 3 .5 and 2.S [() I [
Linear decibel scale from 0
to 10 .
Amplifier Characteristics
Ourput -Amplifier o mput a va ilable at BNC conn eCtor
markeu OUTPUT.
Gain - Maximum of 86 DB == I DB adjusr eJ in 10 DB
sreps with range selector.
Frequency Respo
ns e - 5 ro 500,000 cp s. 2: 3r; if loa Ji ng
abo ve 1 me gohm wi rh para ll el capaciry below 10 pF.
Source Imp edance - Ar 1 kc appro xi ma r el y 3 ohms in
se ries wi rh 0.22 /LF.
l'-bx i111um Ourpur Voltage -70 vo lts po si ri\c, 40 volts
negativ e.
Maximum Lo ading - 30,000 ohms a nd 10 pr:.
Warmup Drift
L es s rhan 0.3 r;. after 15 minutc warmup .
Noise
[0 [() 14 microvol ts RMS referred [() firsr griJ.
Line Voltage Effects
Specified accurac), ovcr tO o volrs ro 130 vo lr s or 2{)O vults
to 2ciO volts line volragc.
Power Supply
[00 [() no vo l ts or 200 ro 260 vo lr s 60 cycles S2 wa rr s. Al so
available in 50 c ycl e version, uesig r1<Hed Mouel .; 05A· S'l
Dimensions
Portable: 8 in ch es wiue, 15 inches hi g h, 10 inch cs Jeep
Rack:
19 inches w iu e, 8 - ~ · . ; , inches high. i:)1 l in ches deep
Weight
Portable or rack: 21 pounds
Ship
ping weig hr : Portable 27 pounds, r ac k 40 pou nu s.
2. OPERATION
2.1 Power Connection
The volrmerer is supplieJ r ea dy [() operatc on 100 ro 1 .'\0
volts 60 cycles power, or 50 cycles, if so ordcred. A decal
mounted adj
ac ent [() rh e power cord indicar es rhis volrage
and
fr equency. For highest srabiliry a magnetically re gu lar.cci
power rransformer is uscd in ril e insr ru111ent. To real ite the
full advantage
of rh e rransformer til e insrrument must be
ope
ra red at rhe spe ci fied line frequenc y.
- 3
2.1.1 -Line Voltage Conversion -T he 30 5A mav
be co nv cned for 200 vo lr s [() 2. ;0 vo lrs wirh instru c-
ri o ns given on rhe sc hemaric d ia gram ar r ile enu of
rhis book.
2.2 Starting Procedure
Insert the rh ree prong power plug into rilc AC (l u ric , or
use
rh e co n ve rsion unit. Muve rhe p ow er sw ir Ul no ON
posirion Red pi lor lighr siloulu gl ow .

MODEL 305A
For initial turn-on, or if instrumenr has been out of use for
2.4.2 - Measurement of Peak-to - Peak Value of
many monrhs, permit a warmup period of at
le asr 30 min-
Unsymmetrical Waveforms and Pulse Trains -
ures. In ocher cases
10 minuees will suffice. Use the follow ing procedure:
PERMIT AIR TO CIRCULATE FREELY AROUND THE IN-
SET TO
STRUMENT. The volrmerer is ca librated in the ve rtical Function Swirch
PEAK·TO- PEAK
position and
is inrended for use in this manner. For con·
venienr reading a tilting device
is provided beneath the case. Polarity Swirch POSITIVE,
if Posirive Peak is High·
er
in Amplirude, or NEGATIVE, if
2.3 Function of Switches
Negarive Peak is Higher. If wave·
TITLE POSITION
FUNCTION
form is not exacrly known, use peak
measuremenr
to determine higher
Power
ON Applies AC Power ro Insrrumenr peak.
If polariry swirch is nor in
OFF Removes Power agreeme::m wirh higher pea.k, the
ac-
METER Depressed
Decreas~s discharging time con- curacy of measurement may be af-
RESET stanr
of derecror from 3.3 to 0.7
fected.
seconds for fast decay of poinrer. Other Controls
As in 2.4.1
When depressed, the reading is
highly in error and no measure·
2.5 Measurement of Peak Amplitudes
ment should be raken in rhis po·
sirion Before making a peak value measurement tile PEAK AOJ
control should be checked for calibrari on.
Tht clleckinl! a ncl
Function PEAK Disables Negative Peak DereCtor readjustment procedures arc outlined under
2.11. 3 ,~
Switch Instrumenr indiGltes Peak Am·
plitude Chan
gi ng rhe position of rhe po.lariry switch may cause a
PEAK-TO· Instrumenr measures Peak-to- switching rransient when making a peak measurement. This
PEAK Peak Amplitude of
Input Wave·
effect may be eliminared by swirching rhe polarity switch
form ro posirive and rben negari
ve shorrly before mc:tsuring.
AMP Connecrs Ourpur Amplifier
ro
The procedure for measuring rhe peak value of a waveform
Outpur Jack depends on its degree of symmer
ry.
Detector Circuit
is disconnected 2.5.1 -
Nearly Symmetrical Waveforms with
Polarity POSITIVE The ourput of the amplifier is in
Positive and Negative Amplitudes in Less than a
phase with the
vo ltmeter input. 1
to 2 Ratio -Proceed as follows:
With function sw itch in PEAK
position,
in Strulllenr indicates
SET TO
positive peak FunCtion Switcil PEAK
NEGATIVE The ourput is out of phase with PoLlfiry
Sw i tcll
POSITIVE ro measure Positive
the volrmerer input.
With func- Peak,
NEGA TIVE to measure
rion swirch
in PEAK posirion, Negarive Peak
instrument measures negarive
peak Orher Contro
ls As in 2 .4 .1
Range MILLIVOLTS Attenuates input signal and In·
Selecror
3.5 to 1000 clicat es full scale voltage. 2.
5.2 - Unsymmetrical Waveforms with Peak
VOLTS
Amplitudes in More than 1 to 2 Ratio. Only rhe
3.5 to 1000 higher peak amplitude can be measured accurately.
Tile lower peak may be calculared
by subtracting rhe
2.4 Measurement of Peak-to-Peak Amplitudes
higher peak
amp litude from rile peak-to-peak va l ue as
measured in 2.5 .
2.4.1 - Measurement of Peak-to-Peak Value of
Symmetrical Waveforms (AC) -Measurement of
SET TO
nearly symmerrical waveforms whose posirive and neg· FunCtion Swirch PEAK
ative amplitud
es differ by less than a 1 to 2 ratio is
accomplished by the following procedure: Polarity Switch Posirion giving Higher Indicarion
SET TO
Orher Controls As in 2.4.1
Function Swirch PEAK-TO-PEAK
Polarity Switch POSIT!
VE
2.6 AC Overload Considerations
Range SeleCtOr 1000 vo lr s and rum coum er-clock·
wise until rhe merer gives a sready
The insrfllmt'nt is dcsigned ro wi thsrnnd se::vere overloads
deAection wirhour damage
to compOllents.
METER Depress
to speed clecay of pointer. The maxillluill AC vo lr age which Inay be applied ro rhe
RESET Release and rake reading or wair for instrument on
rh e four lowesr ranges is limited by rhe max-
indicaror decay imum
allo~·ed \·olragc ro the grid of the first rube::. For an
- 4 -

MODEL 305A
extended time this should not exceed 100 volts peak-ro-
peak.
The input rube may not necessarily be damag ed by
higher voltages applied for a s hort time.
RANGE MAXIMUM INPUT
3. 5 ro 100 millivolts 100V peak-ro-peak or 35 V RMS
350 millivolts ro 1000 V 1000 V peak-ro-peak or 350 V RMS
2.7 DC Component of Input Signal
The voltage measurement by rhe insrrument docs nor in-
clude rhe
dc co mponent of the signal. If rhe dc co mponent
is measured indep e ndentl y rhe complere peak values may
be calculated by
adding algebraicaJJy.
The maximu m dc input ro rhe instrument is lOOO volr s. If
the dc input is grearer, an exrernal capacitOr musr be con-
nected in series
wirh rhe insulared input rerminal. For
measurements do wn w 5 cycles this capaciror should be
0.22 f,F or hi gh er.
2_8
Input Impedance
The inpur impedan ce of the insrrum e nt d epe nds on rhe
se
rting of the range switc h. For ranges of 350 millivolrs
and above, the
input impedance is represeoted by lO pF in
INPUT RESISTANCE MODEL J05A
I
'~
Ial
-,
"
1\.'
~ RANG S 3.~ TO 100 ~ILLIVOLT5
~"'NG[S J~O MILLIVOLTS AND UP
~
'l"
\-...
0.
1 •2 .5 I
KC
10Ke 100 KC
IMC
FREQUENCY
parallel wirh 2 megohms. For ra nge s from 3.5 millivolrs ro
100 miJJivolts rhe
input impedance is 25 pF in parallel with
2 megoluns.
The capacitive comp one nt of inpur imped ance is pr a Cti cally
constant over rhe e ntir e frequency range of the ins rrum ent.
Th e resistive component chan ge s with frequency as sh own
in the following gr a ph.
In normal use with low impedance sour ces, the i nput im-
pedance does nor
present any appreciable loading. H oweve r,
w hen rhe source imp e danc e approaches lO,OOO ohms the
effeCts
of loadi ng should be con side red.
2.9 Use as an Amplifier
The instrument may be employed as a wide-band faSt rise-
time am plifier ro d eliver up ro 70 volts intO a low capaci-
rance
lo ad. For use as an amplifier:
SET TO
Functi on Swirch AMP
Polariry Switch POSIT! VE for I n- Phase OutPUt
NEGATIVE for Re versed OutPUt
5
Ran ge Swit ch
Ran ge ro give Scale Reading or
to a Hi g het Range
Connect input sign al ro input te rminal s and rake o urput
from BNC conneCtor marked OUTPUT. AdjUSt ran ge
swirch for desired
amplificarion wirhout di s[() [[ion.
Amplifier characteristics are described in 1.2,2.6,2 .7 and 28.
To utilize the full freq uency rang e and shortest rise-t ime of
the amplifier rhe capacitiv e load ing at the omput mu st not
exceed 10
pF and the load re sistance SllOUld nut be bc:low
.3
0,000 ohms.
Capaciriv e loading of the outpUt may be increased above
10 pF if fast rise-t im e and wide band-width are nor re-
quired. Th e resistive load ing may also be in cre:ascd if max-
imum ourPll[ voltage is nor necessary.
2.10 Panel Controls with Screw Adjustment
Three adju stable controls ar e provided to the righr of tite
indica
ting met e r.
CONTROL FUNCTION
SCALE AD] Controls rhe Scale Lineari ry
CAL AD] Cont ro ls the Sen siri vity and Calibrarion
of rhe ln str ument. Ad jllJ lliI l?lll of Ibis
c Olltrol (zjJ l?ct s the im l l'llm C Ilt's ,I CCtl-
facy alld shlM ld only b~ lIuder /uk 1/
alter readilJg Sectioll -/ ,6 .3, ,/lid lI' heli
req uired ,ICCllfatl? c( (lib ril lio!l equip-
ment is ({l"tlilable.
PEAK AD] Controls rhe Scale Linea rit y of Peak
measur
em e nt and m ay be Changed [()
allow Peak measur eme nt be l ow I mil-
livolr.
The controls are SCt at Ballantine Laborarories for b es t O\U-
all accuracy on a widc variery of waveforms,
The SCALE AD] and PEAK AD] cont mls may be re-
;Idjusteci ro com
pen sate f or rube aging or f or special meas-
urements as in 2.11.1 and 2 11 . 3. Th ese adjustments shou ld
be checked every 200 homs of operation .
2.11
Use of Adjustable Controls
2.11 .1 The SCALE ADJ control shu uld be adjus ted
wh en an in dicarion of precisel y LO on the up per volt-
age scale does nor produce a reading of I ± O. 2 5' ,
on the lower voltage scale on the nexr hi ghe r ran ge .
The input volrage, of course, mU St be quite cons tant
during this check.
For
general use this check shou ld be made with a sine:
wa
ve . 1£ rhe ins trum e nt is [() be used onl y for m e: a s·
uremenr of a particular waveform or eype of wav,,-
f
orm, rhen the adju st ment may be made usiog this
waveform and hi ghe r accuracy on rhis part icular sig-
nal wi
ll be obtained. Proceed as folluws:
A. Allow 30 minmcs or mure: warmup.
n. Connecr an a mplitude stabk vu lt'1 gc ,o ur, e: ot
approximarely I volt and 1.00 [() :2000 cycles
ro rh e input te rmin als.

MODEl 305A
C. Set polarity to POSITI VE, funerion to PEAK-
TO-PEAK and range to 1000 millivolrs. Adjusr
mpur volrage unril merer reads exactly LO on
rh e upper scale.
D. Switch
to 3.5 volt range. Meter should read L
on
lowet scale. If not, turn SCALE AD] to
give exact ly 1. T ap metet face lighrly during
measurement to teduce friction effects.
E. Repeat C and D u ntil indicated r ange agre es
with arrenuatnt range to within ::'::0. J fJ c.
2. 11.2 CAL ADJ - DO NOT READJUST -See
NOte in 2.10.
2.11.3 PEAK ADJ - is to he .adjustcd if, when
measuring perfectly symm ett ical waveforms , the
PEAK indication is nor exactly 50
rr'
of the PEAK-
TO-PEAK indicatinn .
Procedure:
A. Allow a[ least I hour warmup. Set Function
Switch to PEAK-TO-PEAK, Polarity Switch to
POSITIVE and Rangc Switch to 1000 MILLI-
VOLTS.
B. Connect a stable disrortionless (less than 0.50( . )
sine wave source
of approximately 1 voir and
100 ro 2000 cycles to the input terminals. Ad-
JUSt the inpUt voltage for an indication of 10
on
the upper scale.
C. Set Function Switch ro PEAK The indication
should be exactly 5. If not, adjust PEAK AD]
until an indication of 5 _ 020 % is obta ined.
Tap meter slightly as in 2.11.1.-D.
2.12 Peak Measurements Below 1 Millivolt
The PEAK A DJ control may be ll sed to ext end the volt·
meter range for peak measuremem down to !O microvolts.
This also allows use of the voltmeter as a sensirive peak
responding null derectOr.
Th e frequency range for extended m easurement is the same
as for all PEAK indicarions. The specified accuracy applies,
to which an additional error of = 10 microvoLts is added.
Procedure:
A.
Shorr the input terminal s.
B. Set Function Switch to PEAK, Polariry Switch
to polarity of signal and Range Switch to 10
millivolrs
or above.
C. Set PEAK AD] to givc an indicarion of L on
lower volts scale.
D. R
emove short, app ly signal and set ran ge to ).5
MILLlVOL TS. Pointer will indicarc a slightly
AllCtuaring
reading which Illay be interpreted
using rhe lower volrage scale between I and 2.
I no w corresponds to 0 and 2 corresponds [()
I millivolt. Every subdivision is 50 microvolrs.
When measurement is finished, rhe PEAK AD]
should be reser according [() 2. 1 13 [Q a\'oid errors
in normal me asurement.
2.13 Measuring Short Pulses with Low Duty Cycles
When pulses wirh durarion less rh an I microsecond or
reperition rares below LOO pps are measured, and when rhe
duty cycle is below 0. 002 , a correction should be added [()
rhe rea dings if the readings fall berween 0 and Ii db on rhe
clecibel sca
le .
The correcrion depends up on rhe dury cycle, rhus:
Dury Cycle
Pulse
Widrh In ) Add
To Mulriply
(Sec. X Rep. Rare in Sec. I )
Reading
Reading By
0.0002
ro 0.002
-L 2 ~(
1.02
0.00002
to 0.0002
+ ~ %
[04
below 0.00002
+) 00
106
The measuring error decreases wirh increasing indicarion
so rhar
the readings above 4 db on rhe decibel scale are
wirhin specified accura cy. Wilen correcrions are applied ro
readings below 4 db , the rotal error does nor exceed .:.... 5'; c.
2.14 Techniques for Higher Accuracy Measurements
The inStrument accuracy is specified for rhe SCALE AD]
control set wirh a si ne wave input. This pro vides rhe best
compromise berween accuracy and variery of measureable
waveforms in normal use.
Generally, if accuracy is foremosr, Peak-to-Peak measure,
ment should be preferred ro peak measurement, or if peak
IneaSllrementS are made rhe PEAK ADI should be checked
according to 2.11.3. .
For some special waveforms higher accuracy measurements
arc possible when rechniques described below are used.
2.14.1 Mea s uring flar rop waveforms, pulse trains
and
square waves may be made up ro 1Ct' more ac -
curate by serring the SCALE AD] widl rhe particular
waveform as described in 2.11.1.
2.14 .2 In measuring below lO cycles ser POLARITY
Switch ro NEGATIVE
2.14 .3 When me asuring beJow ) millivolrs, the noise
of rhe input srage affecrs rile accuracy. This noise is
app r oximare ly 10 to 12 microvolrs rms as referred
to rhe firsr gr id. The actual error depends upon the
signal a
mpliw de and waveform. For sine wave rhe
correCtions
are rhu s:
AT CORRECTION
MiJlivolt --4 ~ ~ ;
.3 Millivolts
-15 %
Abo\ 'e "i Millivolts rhe noise error is negligible.
2,15 Use as an Ammeter
'V(fhen rh e M odel 305A is coup led wirh the Ballantine Series
600 Shunt Resisrors, peak currents from I microampere ro
G

MODEL 30SA
10 amperes may accurately be measured. These and other
accessories may be found in the gene ral catalog of Ballantine
instruments .
2.16 Measuring Above 1000 Volts Peak
With the Ballantine Model 1305B Voltage Multiplit:r, the
range of the 305A may be extended to 28 kilovolts Peak·
1O-Peak.
2.17 Power Line Effects
The instrument is operative from 80 volts ro 140 \'olrs and
58 cycles 10 65 cycles.
Line vatiations from tile specified operating voltage affects
the accuracy of the instrument by appro ximately :::!:::0.15 ~
per lOc-E of line voltage chang e.
Line
frequency variations change the accuracy by approxi-
mately 0.5t;' ;:' per cycle deviation from 60 cycles.
2.18 Effect of R. F. Line Transients
Line transients may enter rhe instrument through tilE:: inpur
circuitry and affect the indication. Careful shielding of the
inpur leads is a necessity when the power line cont ains large
transients of this type and accurate measurements are dc-
sired.
The voltmeter does not respond to these transic11ts
rhrough irs own power cord.
3. CIRCUIT DESCRIPTION
The block diagram, schematic and replacement parts list are
included at the end
of rhe instruction book.
3.1 Input Attenuator
The voltage 10 be measured is applied through the input
sending parts and dc blocking capacirot C I 10 the input
atte nuaror. This arrenuaror is at lower frequencies a resis-
tive
divider and presenrs a 2 megohms load to the input
signal. At higher frequencies above 25 kc the arrenuator
becomes a capacitive divider. The dividing r atio of larr er is
adjusted 10 the co rr ect va lue by trimmers C2 and C3. Th e
attenuation ratios are as follows:
Range Swicch Seuing
fULL SCALF.
Inpu[
AI[.
Anenua[ion Rario
Mid.enion AI[. TOlal
35mV
I 1 1
10 mY 1 3.162 3
162
35
mY
I 10 10
100 mY I 31.62 31.62
350
mV 31.62 3.162 100
1000
mV
31.62
10
316.2
3.5 V 31.62 31.62 1000
10
V 1000 3.162 3 1(,2
:'>5
V
1000
10 10000
100 V
1000
31.62 31620
350
V 31620
3.162 100000
1000 V 31620
10
'>1(,200
3.2 Input Amplifier
The input amplifier consists of twO capacitively coupled
penrhode stages V 1 and V2 followed by a direer coupled
split-phase invert er stage V3. The amp lifier has over 40 db
negative feedback at midfrequencies with the ro ll- off rate
of 6 db per oerave at the high and l ow frequency ends. Th e
r
espo nse at the high frequency end is adjustable ro a limited
amount by variable capaciro r C6
The first stage rube V I is shock-mounred and shie ld ed ro
reduce
microphonics and hum pickup. First and second
stage heaters are
()ptr~[(:d with de. Tht plare voltage of
direcr
coupbl stagt V2 can be adjusted wirll rhe scrc:en
snits resisror R 18. Neun bulb NEZ prorecrs V3 in case of
V2 failure or removal.
The Polarity swi tch S2 connects the following buffer stage
ro the plate or cathode of the phase inverter stage V3 which
inverts the phase of the signal so that pulses will always
drive ourput amplifier positively to assure faSt rise-time and
rrewnr cur-off of rhe outpur stage.
3.3 Buffer Stage and Midsection Attenuator
Buffer stage V4 is a cathode follower which couples the
high source impedance of the plate of input amplifier ro
rhe relatively low resistance
midseerion attcnuaror. To
eq ualize the high frequency response of the plate take-off
(NEGAT IVE ) with the high frequency response ro the
ca thode take-off (POSIT IVE ) a variable capaciror CIS is
connected 10 the cathode when signal is taken from the
plate.
The midsection atrenuaror is a four-step string attenuator.
Over most of rhe frequency range it acts as a resistive
divider. Fixed
capacitors C 1.8 and C 19 provide correction
at the highest frequency range of the instrument.
3.4 Output Amplifier
The ourpUt amplifier consists of twO capacitively coupled
penrbode stages V5 and V6 and a direct coup led cathode
follower V 7. The l oop feedback is approximately 38 db ar
midfrequencies with a roll-off rate of 6 db per octave ar
both ends of the frequency response. The high frequency
response
is slighrly ad j ustable by the variable capacitor C20.
The heater of V5 is operated with de. The plare voltage of
V(i may be adjusted with screen resisror R.:"i I Neon bulb
V8 limits the cathode volrage of V7 during the warmup
period and proteers the rube.
3.5 Peak-to-Peak Detector
The outpur amplifier is connec red o\'er G,paciror C26 and
function switch S3 ro rhe peak-ro-peak detector which co n-
sists of
twO vacuum diodes. V 12 for positive and n eg ative
derection and a charging capaciror C32. Divider R57, R58
provides a de bias to the detector.
The diudes charge capocitor C.\2 with a short rime constant
of approximarely DO l microseconds. C32 disch,ages over
a 22 megohm resisror R59 wirh a rime constanr of 2.2 milli·
7 -

MODEL 305A
seconds. A high discharging-charging rime consranr rario
insures rrue peak derecrion
of rhe inpur signal.
Th e derecror srages are conn ecred ro rhe differenrial carh ode
follower V 13. C33 berw een rhe grid and carhode of V13 in-
creases rhe derecror efficiency for low
reperirion rare pulses.
3.6 Pulse Stretcher
Th e differenrial carh ode follower V13 which acrs as an
impeda nce rransformer feeds rhe sig nal ro anorher pair of
peak recrifiers V 14 which rogerher wirh condensers C34
and C35 are charged ro rhe peak value of signal. The dis-
char
ge over resisrors R63 and R64 has ve ry long rime con-
sranr
of :'>.3 seconds so rh ar rhe peak charge on C34 and C35
;rays almosr consranr, even berween a pulse rrain for repe-
tirion rare
of S pps.
f
or fasr disclnrge R62 :lnd R65 can be connecred parallel
ro
R63 and R64 by opera ring rhe METER RESET Sw itch S4.
For peak·ro·peak measurement borh capac irors C34 and C35
arc co nn eered ro rhe second differenr ial ca rh ode follower
V 1
5. For peak measurement rhe negarive channel of rhe
pulse srrercher is disconnected by FunCtion Swirch S3 and
an adjusrable bias ove r rhe divider R66, R68 a nd PEAK
AD] R67 is fed ro rhe carhode follower. Wirh PEAK AD]
rhe scale lineariry for peak measurement is controlled.
3.7 Measuring Stage
Th e carhode follower V15 feeds a shaped pole piece moving
co il indicaror. The current range of rhe indicaror from 0 to
10 db is 190 ro 600 microamperes.
The CAL AD] conrrol R76 in series wirh rhe indi caror
changes rhe volrage sensitiviry of rhe indicaror and is used
to ser rhe sensiriviry of rhe insrrumenr during calibrarion.
Th e SCALE AD] conrro l R70 affecrs rhe bal ance of rhe
differential
carhode follower. Ir inAuences rhe on-scale in-
dicarion more rh an rhe fu ll scale indica ri on, and so is used
ro
conno l rhe scale lineariry of indi ca ri on .
The hearers of all rubes in rhe peak derecror-pulse srretche r
circuir are regulared ro assure high srabiliry of balance
againsr line ,·olrage va ri arions.
3.8 Power Supply
A consranr volrage rransformer rogerher wirh clccrronic
r
egularion is used in power supply to srabilize rhe hearer
and +B voltages
and achieve exce ll enr srabiliry againsr line
volr
age changes and rransienrs. A silicon reerifier volr age
doub l er circuit is used in rhe +B recrifier cirOJir. Three
se parate filamenr circuirs are used. One XX for rub es in
power supply, one YY for amp lifiers, and a recrified de
filament for rubes V I,
V2 and V5.
4. MAINTENANCE
4.1 General
4.3 .2 A dc volrmerer I voir ro SOO volts with 10 meg ·
ohms inp ur resistanc e· 3~ o accuracy. (F or checks
Th c insr rumenr IS designed tor an exrend ed period of
4.2.2 and 4.
2.3.)
r roub l e·f r ee service. Th e l oading of compo n ents and rubes
is
kepr we ll bel ow rarings, rhe rub e heat ers arc r egulared
4.3.3 A volr age ca libr arcd (::!: O.S ':'£' or bener) dis-
and rhe
opera ri ng r emperarure of a ll compo nenr s is low.
ronion-free so urce, 400 cycles ro 2 kc (s uch as Balian·
Ir is expected that under normal laborarory use rhe rube
rine Model 420 Precision Ca libr aro r or an accurat e
life will exrend
ro 4000 ilours wirhour need for recalibrarion
J... o.srf or b ener) volrmerer wirh srable disrortion·
of rhe insrrumenr.
When rhe mbes are replaced wirh rubes free volta
ge source. ( F or resrs 4.2.2 and 4.2.3.)
of
normal charaererisrics rhe vol rmerer performanc e will be
resror
ed wirhout rhe ne ed of exrens ive calibrarion.
4.3.4 A rube cheekltr wh ich mcasures ru be rranscon-
ducrance.
(For resr 4.2.3.)
A
periodic mainrenance as desc ri bed below is recomm ended
to guaranree tile maximum accurac), of rhe instrum ent and
4.4 Removal of the Case
help
prevenr possible breakdowns in service .
The resrs 4.2.2 and 4.2.3 require rhe rcmoval of rhe case,
which can be done as follows:
4.2 Recommended Maintenance Procedure
a. Place ril e insrrumenr with rhe front panel down on
Th e fo ll owing periodic c il ecks are r ecommended.
a table .
4. 2.1 Every 200 hours a scale and peak ad j ustment
b. Rem ove rile powe r cord, unscrew rhe rhree ,f I0 binder
check. head screws
from rile back.
4.2.2 Every 1000 hours a 1000 hour cileck.
c. Lift up the case.
4.2.3 Every 2000 hours a 2000 hour check.
To pur rhe case back proceed in reverse order.
WARNING: WHEN INSTRUMENT IS OPERATED
4.3 Necessary Maintenance Equipment
WITHOUT THE CASE THE DANGER OF ELECTRIC
To perform rhe rests li sred undtT 4.2 rhe following e quip.
SHOCK EXISTS. EXERCISE EXTREME CARE.
ment is n eeded:
Th e hig hesr ,·olrages are:
4.3.1 A variab le ourpu r ( app r ox . I voir) sr ab le vo ir ·
age
source 400 cycles co 2 kc wirh below OJ' ,; wave·
On Power Supp l ), C ha ss is
SSO Volrs ;\C
form distonion. (For ellccks 4.2.1,4.2.2 and 4.2.3.)
On Amplifie r Chasis
300 Volrs DC
. 8 .

MODEL 30SA
4.5 The 200 Hour Check d. Remove the instrument case (See 4.4),
This serves ro check the adj ustment of PEAK AD] and
e. Shunt, or add in seties an Allen-Bradley Type
SCALE
AD] controls and is performed according ro th e
En \.j watr resistor ro R2 l. Add the series re-
2.11.1 and 2.11.3.
sistOr when the POSITIVE response is higher
than the
NEGATIVE re sponse. 100 ohms gives
approximately I(
i., corr ec tion.
4.6 The 1000 Hour Check
This entails a check of the general performance of the in- Shunt R21 when the
NEGATIVE response is
strument and consists of the following tests: higher. 1 meguhm gives approximately 1'I
f: cor-
rectio
n. (Fig. 2)
Correct the SCALE
AD] and PEAK AD] as described
under 2.
11.1 and 2.11.3. R21 is located between rh e Pin 5 of Tube V3 and
rhe lowest terminal boatel on the amplifier chassis,
4_6_1 Check the dc coupled stages V3 and V7 as fol-
lows:
4.6.3 A check of the CAL AD] control should be
made only when an accurarely calibrated voltage sou.rce
a. Remove the case (See 4.4 ). (4.3.3)
of good waveform is available.
b. Shorr the voltmeter input terminal, set the range A
0.5 s" i or more accurate RMS or average responding
switch
ro 1000 volts, connect the power cord, laboratOry smndard instrument could be
used with a
turn the instrument ON. 400 cycle
to 2 kc distOrtion-free voltage somce. Line
c. After 10 minutes warmup measure the dc voltage frequency
is not suitable for calibration purposes be-
on Pin 7 of
V3 and V7. The voltage should be-
cause of high disrortion and tOO low frequency. \X/hen
an RMS calibrated instrument
is used as a standard
50
to 68 volts for V3 and the conversion
fr om RMS to peak-ro-peak can be made
100
ro 115 volts for V7.
as follows:
When the voltage is out of limits rhe tubes V2 or V6
I volt Peak-ro-Peak = 0.354 volts RMS of sinewave
should be replaced. Any rube within the manufaCturer's For CAL AD] Check, proceed
as follows:
specifications
is suitable for replacement. However, for
highest stability, mb es with approximately 50 hours of
n. Allow a minimum of OJ hours warmup.
aging under similar conditions
as in the: voltmeter are
recommended.
b, Check SCALE AD] as described under 2.11, l.
c. Apply accurate I volt Pcak -tO- Pe ak ±0,259( to
After tube replacement the Pin 7 voltage should
be
the voltmeter.
adjusted
to following limits: Set -Range Swirch
to 1000 mV
Pin 7 Tube
V3 60 volts ro 68 volts Function Switch
to PEAK-TO-PEAK
Pin 7 Tube V7
106 volts ro 116 volts Polarity Switch
to POSITIVE
The adjustment is made by conneCting an Allen-Bradley Adjust CAL
AD] to give an exact reading of to on
Type
EB 1/, warr resistOr in series or in parallel with
the:: upper voltage scal e. Tap the meter slightly before
R
18 or R4 L An inct ea se in R 18 or R41 will increase raking the reading.
the
vo ltage. A decrease of R IS or R41 will decrease
the Pin 7 voltage.
4.7 The 2000 Hour Check
4_6.2 Checking the Phase Inverter for Symmetry -Includ
es all checks described under 4.6 PLUS the tube check
Proceed
as follows: and the power supply check.
a, Connect a disrortion-free sine wave source (4. 3.1
4.7.1 Tub es should be tested for proper transconduct-
or 4.3.3)
to the input of the voltmeter. ance and
low grid current. Any common tube testcr
may be used for the transconductance test. Tubes
b. Set Function Switch to PEAK-TO-PEAK with transconductance below the manufacturer's limits
Range Swirch
ro any range 350 mV ro 3.5 Volts should
be replaced.
Polarity Switch
to POSITIVE
The grid current oi Tub es VI, V2 and V6 should be
Adjust the input voltage to produce an acc urarely measured
by J1lL':l suring the grid voltage at Pin I of
readable indication at any point
in rhe upper 1/3
rhose tub
es wirh range swirch ser [() 3.5 millivolts and
of
th e meter scale. Nore the indication, rhe
inpLl[ co rhe volrmerer shorreJ, The maximum grid
c. Switch rhe PubriC)' Swirch ro NEGATIVE Nute
vol rage is:
rhe new inJic<ltion.
Tube -I 0. 05 V
The rwu indicarions should not differ more than
Oj ~ ( If the difference is more rhan 0.5'; (: cor-
Tube 2 - 0.2 V
recr
as follows:
Tub e 6 - 0.2 V
- 9 -

MODEL 305A
Tubes which measure a higher grid voltage should be
Tube 9. This voltage should be 300 V to )10 V. If the
replaced. voltage
is Ollt of these limits it should be brought with-
in them by adding to, or shunting R56 with Allen-
Tubes which measure normal do not have to be re- Bradley
Type EB resistOr. (Fig. 4).
placed until tra nsconductance drops, or grid cu rrent
or some Other fault is observed . Tests ar Ballantine
If Tube VI 0 in the power supply is replaced, the power
LaboratOries indicate that this may take over 10,000
supply ripple at Pin I of Tube 9 should be checked as
hours of operation described under 5.9.2, page 13. If the ripple is more
than 12 mV pp adjustment of R49 should be made to
4.7 .2 +B voltage should be measured at Pin I of
bring the ripple inro 12 mV pp limits.
5. SERVICE AND TROUBLE SHOOTING
5.1 General 5.3 Simple Service Problems
In case of volt meter malfunCtion, limited servIcing by the
5.3,1 Pilot Light Replacement is acco mplished from
user
is feasible provided sk illed per so nnel and recommended
the front. Afrer unscrewing rhe red plastic cap the
eq uipment are available and the procedur es outlined below bayo
net base pilot light can be removed and replaced.
are followed.
5.3.2 Fuse Replacement - The fuse is Slow-blow
However, it should be
pointed OUt that the described pro- type
(Bu ssman MOL or equivalent) rated I amp for
cedures are only simplified outlines of recommended service
11 5 and 0 .5 amp for 230 V operation and may be re-
and calibration. Refined service and
comprehensive calibra- placed by unscrew
ing the fuscholder cap on rhe froor
tion requires accurate and special equipment normally nOt
panel.
available to
the user. Therefore if trouble develops which
ca nnot be corrected by the simplified meth ods outlined here Befo
re replace ment , the reason for fuse failure should
or when accurate recalibration of the instrument is needed,
be investigated and corrected.
Normally it will be on
it is recomm c: nded that the voltmeter be returned to Ballan-
the prim a ry side of rhe' power transformer. Because of
tine LaboratOries for service and / or recalibration . If it
the special nature of the regulatOr transform er a short
should
become necessary to rerum the instrument or any in
the filament or +B circuit doe s not nec essarily burn
part thereof to Ballantine LaboratOries, Inc. for examination
O llt the fuse n or harm rhe power transformer.
or se rvicing, at least 4 inches of packing material should be
placed
around all sides of t he instrument to prevent damage
5.3 .3 Tube Replacement - This may be done after
during s hipment . Ship via Railway Express or m otO r truck.
removing the case (see 4.4). Any tube within tllbe
A
letter de sc ribing rhe trouble or desir ed service will help
manufactllrer's specificarions can be llsed for repl ac e-
our Service Departm e nt greatly and insure a fast reruro. ment . When replacing tubes V2 and V5 pr eag ing of
the tubes for a pprox imately 50 hours is rec om mended .
After repl ac ing rhose rubes the DC voltages should be
5.2 Necessary Equipment
checked and ad justed according to the instrucrions in
4.6.1.
For successful servici
ng and trouble shoOting, the following
equipment is nee ded : 5.
3,4 Conversion to 230 V Operation - After re-
moving the instrument from rhe case (see 4.4), can·
5.2.1 A DC Voltmeter, I Volt to 500 Volts Full Scale sulr
the wiring di ag ram at tbe end of the instrucrion
± ~'7(, 10 megohm input resistance (Fo r Test 5.4).
book for detailed informari on.
5.2.2 A sensitive AC vol tmeter, LO cycles to 100 kc ,
5.4 DC Voltage Checks
I millivolt to 100 volts, ± 300 (For Test 5.5 ). BaLlan-
tioe Model 3 00, 300 0, 31 OA, or 302C would be suit- A
check of the DC voltages on tube pins should be und e r-
able for tbis purpose.
taken when the voltmeter sho ws malfuncrioning which
cannOt
be corrected by tub e replacement.
5.2.3 Signal Generator 10 cy cles to I Mc, 1 volt output
(For Test s 5.5, 5.6, 57) . For DC volt age measurement proce ed as follows :
Rem ove the case (4.4)
5.2.4 Approximately ca librated sensitive oscillos cope
DC to 1 Mc (For Te sts 5.6, 5.10).
Sh ort the input terminals
Set - Ra nge Switch to 1000 V
5.2.5 Accurate volta ge calibrator, I volt:::!:: 0.25% ,
Funni on Swirch ro PEAK-TO -P EAK
kc , such as Balla ntin e Model 420 (For Te st 5,5) . Polarity
Switch to PO SITIVE
5.2.6 Accurate HF voltage sourCe, such as Ballantine Measur e tube pin voltages with a 10 megohm inpur resis t-
Micropotentiomerers or Mod el 39 3 Voltmeter (For
ance voltmeter and compare the r es ults wirh the fo ll o wing
Tesrs 5.6, 5. 7).
rable:
-10

MODEl 305A
TUBE PIN VOLTAGES MEASURED TO THE CHASSIS
2
1 4
3 5 0 7 8
~
9
TUDE
VI 0
0-0.05 2.1 6.1 110
2.1
90
V2 0-0.2
12 .2
1.5 18.3 55-65 100-130 l.5
100
V3 100
55 -65 235-255 235-255
235-255 56- 68
V4 100
250 100 250 110
250
V5 0-005 6.1 12.2
90-140
100-130 1 5
15
Vo
100
0-0.2 100
1.6 100-113 130-160 1.6
V7 100-113
300-310 100 100 300-310 10 2-115
300 - 310
V9 300-310
150 150
295 150 295
3R5
VIO 105 150
107 150 295 107
150
VII
107 107
0 0 -0
-
VI2
70 100 100
70 -
70
-100
VI3
300-310 100 100 300 - 310
70 93
93
VI4
90·
100 100
93
93
93
JOO
VI5 100
90·
300 100 100
100
300
90
"Measnreu with METER RESET depressed.
All voltages, unless
otherwise specified, should be within
_ 10% of the TABLE VALUES.
Tube Pin
No_
Tube Element Voltage V RA'
IS
VI
I
Control Grid
0.011
VI
2 Carhode 0.0107
V2 I
Control Grid
0. 0075
V3 I
Control Grid
1.45
V3 7
Cathode
136
V3
2,5,6
Plate L'>6
V4 I
Control Grid
])6
V4 7
Cathode
130
V5 1
Control Grid
0_13
V5
2_7 Cathode
0,126
V6
I
Control Grid
0, 13 roO. 16
V6
5 Plate
235
V7 I
Control Grid
235
V7 7
Cathode
225
VI2
1
Cathode
22.5
VI2
2 Plare
225
If any voltage is outside the sp e cifi~d limit the associated
tube should be checked, co
nn ecrions inspected and compo-
nents measuted until the reason for voltage Jeviati on is
found and correcred .
-
5_5 Signal Tracing
If the reason for the voltmeter malfunction cannot be found
by a dc voltage check, signal ttacing siloulu be used to locate
tile trouble.
For signal
tracing apply a I volt Peak-to-Pea k (0. :;5 voll
RMS ) 1 kc signal ro the input of the voltmet er and set:
Range Switch ro I VOLT
Function Switch [Q PEAK - TO - PEAK
Polarity Switch ro POSITIVE
Use a sensitive high inpur impedance voltmerer (5.2 2) ro
measure the AC voltage ar tube pins listeu in the table be-
low.
The measured voltages should be within = 10 % of
the listed values.
If
disag r eement with the tabulat ed voltages is found, rhe
whole amplifier in
which the discrepancy is found should
be checked since in feeuback amplifiers trouble in any of
rh e stages will likely affect voltages el sewhere in the circuit.
If all signal voltages measure normal and the incorrect
indic ation is still observed, the peak detecror circuit should
be checked as follows:
With I volt Peak-to-Peak and rhe VOlrrllClE:r (o t1 {[ ul,
set as
ab ove rhe uc cathode vult: 1!,! es of rubes V I ; :w ,l
V 15 should be measureu. Thi s me asurement should be
II -

ADJUST INPUT' AMPLIFIER ADJUST
ADJUST OUTPUT
AMPLIFIER
100 mY, 400 KC
SEC. 5.6.
ADJUST " NEG"
RESPONSE
100 mY, 400 KC
SEC. 5.6.
PHASE
INVERTER
400 KC 100mV, SYMMETRY
SECTION
5.6
SECTION 4.6.2
Fig. 2

MODEL 30SA
repeated with thc same input signal but with the range
switch on 3.5 volts FULL SCALE.
The voltages should be:
TUBE PIN I V FS 35 V FS
VI3
3
120
104
V 13 8 9-i
97
V 15
3
130
112
VI5 8 80
97
5.6 Amplifier Frequency Response Adjustment
This should be corrected when the voltmeter gives a correct
indicarion on rhe 3.5 millivolr FuU Scale Range ar mid-
frequencies (400 cycles ro 2 kc) but an excessive error ar
higher frequencies .
The adjusrment of the amplifier respons e should be made
after replacement of defective rubes and compon ents and
after the midband accuracy according ro 4.6.3 has been
checked or corrected. Also, Capacirors CIS and C19 should
be checked.
To correct the amplifier frequency response proceed as
foll ows:
a. Remove the insrrument from rhe case ( 4.4).
b. Set Range Switch ro 100 mV
Function Switch ro PEAK-TO·PEAK
Polariry Switch ro POSITIVE
c. Connect a 15 ro 30 millivolt rms microporcntiom ete r
to the voltmeter input and a generaror with less than
0.5% distortion ro the micropor e ntiomctcr , as shown
in following diagr am.
MICRO MODEL 305A
R.F
PEAK
POTENTIO
~ f-+-
GENERATOR
VOLTMETER
METER
t
D.C.
MICRO-
AMMETER
d. AdJust rhe signal level ro some convenient point on
rhe scale and take the reading.
e. Keeping rhe microp o rentiomerer output constant, in·
crease rhe frequency ro 400 kc. The voltmeter should
indic a re 0,5 ro 1 C;c below the previous reading . If nor,
adjust C6 and C20 ro specified limits. Adjustment of
C6 and C20 should be made so rhar borh rrimmers will
have approximately the same capaciranc e value. The
locarion of C6 and C20 is shown on phorograph (Fig.
2) .
f. Turn rhe Pulariry Swirch ro NEGATIVE Adjust C!5
until merer gives rhe same indicarion as in POSITIVE
posirion.
5.7 Attenuator Frequency Response
Adjusrment should bc made when the \' oltmeret ex hibits
excessive error at higher fre quencies on ranges 350 mV to
3.5 \'olrs
or 10 volrs to 1000 volrs. The adjusrment of ar·
renuaror frequency response sh ould be underraken only
afrer
rhe amplifier freCJuency response has been checked or
corrected . The adjusrment of rhe 10 volts to 1000 volts
range should be done befor e rhc adjusrment of .J 50 milli·
volrs to 3.5 volrs range because the first adjusrment affecrs
the second.'
To a djust rhe arrenuator re spo nse proceed as follows:
a. Rem ove rhe Range and Polarit y Swirch Knobs and
Escutcheon Plan : by removing four ~. ! binder head
screws
from rhe front panel
b. Replace rhe range swirch knob and turn rhe switch
four posirions back fr om rhe mosr clockwise pos irion
( 10 voir range).
Set Function Switch to PEAK·TO·PEAK
Polarity Swirch ro POSITIVE or NEGATlVE
c. Apply 1 kc 3 to LO volts Peak-ro-Peak disrorrion·frce
s inewave ro rhc inpur. Set the input boel to a con ·
venienrly readable poine on rhe scale.
d. By means of it Ballantine Model 393 Typ e C Volt-
merer or equivalent accurare device keep rhe inpur
volrage constant wirhin 0.25% ; change rhe frt'quency
ro
200 kc.
e. Adjust rrimmer C2 wirh an insulated screwdriver until
rhe indication is exactly rhe same as for 1 kc. For lo-
cation of C2 see photograph (Fig . .').
To adjust rh e 350 millivolts to 3,5 volrs ranges proceed as
follows:
a. Ser the rang e swirch to rhe sixrh position clockwise
( 1
voir).
b. Apply a I kc approximarely 1 voir Peak-to· Peak dis-
rartion·free sinewave ro the inpllt and set the level to
a conveniene poine on rhe scale.
c. Keep the inpur voltage consrant rLl 0.25 '12 and change
the frequency ro 200 kc.
d.
Adjust Trimmer C3 with screwdriver until the indica-
ri on is exactly the same as for 1 kc. For loc ation of C3,
see photograph ( Fig. 3) .
e. Replace the escutcheon plate and knobs.
5.8 Replacement of Attenuator Resistors
The arrenuaror resisrors arc stable and carefully matched in
value, rem
perature coefficient and HF characreri srics. Th ey
do not dissipat e any puwer and ir is very unlikely rhar
troubl e with arrenua tor resistors will occur. Therefure, before
changing any resisrors, a careful check should be made for
, lOy orher source of rroubk: such as lo ading rhe attt'n U;Hu[
by a rube which draw s g riJ current, erc. Aft er all p"s, ible
ClUses a
re: inH,srigared and rhe ins([umt: [1[ still i" in C rfll[
on sume: ranges at luw frequenLies (app roximat ely I k ... "
the art<:nuators
should be irwcsri gar<: d. Ever) ' porrion of in·

Fig. 3

MODEl 30SA
pur and midsec ri on a rrenuaror is used in several ra nges as
marked on rhe w iring di agram. Th e group of ranges which
show rhe error will be rhe gro up wirh rhe faulry a rr e nuaror
and rhe spec ifi c resisror can easily be der ecr ed .
To correer an a((enuaro r res is ror, rhe va lu c of rhe suspeered
resisror, rogerher wirh
orher resisrors in rhe same arrenuaror,
should be measured accurarely 10 0.1 %. The measured valuc
should be w
irhin llir of rhe value srared in rh e partS lisr ar
rhe end
of rhe insrru crion book. H oweve r, rhe arrenuarion
rarios figures
from rhe measured resisrance va lu es sho uld be
within 0.25% of rhe values srar ed on Table , pa r. 3.1.
If rhe arte nu arion va lue differs bi more rhan 0.25 % , rhe
faulry resisror should
be replaced wirh a selecred res i sror of
correer value and of rhe same type and make, since rhe
seleerion of o
ne wirh 0.25 % accuracy is highly i mpract ic al
for mosr
us er s. It is srrongly re com mended rhar rhe vo lr -
merer
be sent 10 Ba llantin e Laborarories for service when
such rrouble occ ur s.
5.9 Servicing the Power Supply
The power supp ly shou ld be checked if rhe fi l ame nt or + B
vo
lr a ges are nor normal, or excessive err or is observed when
measuring 60 (50) cycles or 1 20 ( 100) cycles sigm l or
when indicarion is unsrable wirh srable signal input.
5_9.1 Shorts in filament or + B circuit do nor nor·
mally cause rhe fuse ro blow becaus e of rhe ch aracte ris-
rics of rhe power
rransforme r. Tbis also does nor dam -
age rh e rransformer .
Sm a ll deviarions in +B vo lr age from + 3 00 to +3 10
volrs measured on Pin 1of Tube 9 should be correned
as de sc rib ed unde r 4.7.2.
If rhe
+B measures approximar e ly 250 vo lr s and hear-
er volrages 4.5 volrs
rIllS . a shorr circuir in Tub es 9 and
10 filament may be suspecred.
If rhe -t-B measures approximare ly 150 vol rs and all
rubes look unJir, a
shorr circuir in rhe amplifier fi la -
ment circuirs may be suspecred.
A shorr cir cu ir in +B circuir or defeerive by-pa ss or
fil rer capaciror causes rbe burn our of Rilli and resulrs
in no
+B voltage .
5.9 .2 Excessive Hum in +13 Volra ge or Tub c:s VI ,
V2 or V5 filament circuir causes a high e rror when
makin g 60 (50) cycle or 120 ( 1 00) C) ,cle measure-
ments, and incre ases (jQ (50) cycle: ro 120 ( 100 ) cycl e:
compon enr ar rhe am plifier ourpu r wirh shorred input.
In a no rmal insrrument r he amp lirude of ra n dom noise
e quals rilar of GO cycle or l 20 cy cle component.
The peak·ro-peak hum amplirude on Pin I of Tube 9
co uld be measured by using anorber peak r espondi ng
vo lrmerer or calib rared oscilloscope If rhe h um is
hi gher rhan spec ified, T ube VI O should be changed or
R49 or R 50 shunted by an Allen-Bradl ey Type EB
resistOr. The va lue of rhe s hunt rcsisror ca n be founJ
exper im entally a nd wou ld be g r ea rer rhan I megohm.
( Fig. 4 ).
5.9.3 Instability of Indication in f orm () f rand,)111
pointer il ucruarion above lOO millivolr ran ge s may b
caused by a fautry ref er ence T ube V II \\ hich s ho uld
be replaced. [f rhe instabiliry o ccurs on sensir i\t' rangt's
of rhe
insrrum e nt , shielding of rhe inpur wirin g sh uu l
be check ed for RF pickup .

AD), RIPPLE
ADJ. + B VOLTAGE 300 TO 310 V
SEC. 5.9.2.
Fig. 4

MODEL 305A
5.10 Trouble Shooting
Pertinent
Symptoms
Possible Cause Section
lns[[um e nt inoperariv e
Pilot ligln does nor
lighr
Merer indicaring wirh
no
Inpur
M icro ph onics
No power
Blown
fu se 5. 3.2
Def ecr in power s up p l> '
Inpur n or shiel de d,
picks
up hu m
PEAK AD J o ff 2. L 1.3
Def ecrive rube ( hearer
ca
th ode lea k)
Microphonic tube V I
or V5
Loose connecrion
High err or ar GO (50 ) Hu m pickup in rhe
a
nd 120 ( LOO ) cycle co nn ecr lO ns
m
eas ur emenr Gro und c urr e nt in
meas
uring cir cuir
Strong
mag neric fi eld
Hearer
da mag e in V I,
V2, V5
Hi gh hum of power
s
uppl y 5 9.2
Un stable indica ri on Ins
uffi cie nt shielding in
Inpur wlfJng
Def ecrive VII
Defec ri ve pow er supply 5. 9
Inac
cur ate peak Misadjusred
PEAK ADJ
2.11.3
me asur eme nt
Defec ti ve V6
Impo ssible to ser
Tub es V12, V13, V1 4,
SCALE
ADJ
VI 5
Re
si st or s R70 , R7
,R 74
High error in l
owe r SCALE
ADJ needs 2. 11.1
parr of rhe scale
adjus rme nt
Error in NEGATIVE
Def ecrive ResistOr
posirion only R 2 1 4.6.2
Hi gh frequen cy re- Frequency
re sponse of 5.6
s
pon se or short pulse
the am pl ifi ers or
5.7
mea s ur eme nt In error
arrenuatOrs incorre cr
in POS and
NEG
p os ition
Same in
NEGATIVE
Cl 5 m is adjusr ed 5.6
posirion on
ly
DC Vol ra ges abnormal
Dd ec ri ve po wer suppl y
59
V <) , VII
S hurr in rubes or ci rcuir
- 14 -

MODEL 305A
REPLACEMENT PARTS
LIST
REFER TO MODEL 305A SCHEMATIC DIAGRAM , DWG. No. ME-2936B
B.L. Ci-twit
Part N o.
Symbol Capacitors Mall!l/acilirer
2363 Cl
.1 I" F, 600 Y, 5 ~ , Type 663-UW
Goodall
2438 C2 1-5 pF, Type 5MlI-160-102 E. F. Johnson
2429 C3 7-45 pF,
Type 503-27 Erie
225 [ C4 62 pF, 500 Y, 5
C; c, Type CM-15 Areo
2255
C5
),300 pF, 500 Y, 50;, Type CM -2 0 Areo
2429
C6 7-45 pF, Type 503-27 Erie
2236 C7 200 pF, 500 Y, 5q ,
Type CM-15 Areo
2752 C8A 10
I-'F, 350 Y, Type DFP
Sprague
2752 CSB 50
I-'F, 350 Y, Type DFP
Sprague
2752 CSC
60 I-'F, 350 Y, Type DFP
Sprague
2"72
C9
.022 I-'F, 200 Y, 109(, Type
I92P
Sprague
2753 CIOA
20 I-'F, 300 v, Type DFP
Sprague
2753 CIOB 20
I-'F, 300 Y, Type DFP
Sprague
2753
ClOC
30 I"F, 50 Y, Type DFP
Sprague
2080
Cll 35 I"F, 6 Y, Type 30DI32
Sprague
2510
CI2 .47 pF, 10 %, Type QC
Qualiry
2367
CI3 .1 I-'F, 200 Y, 10 llf , Type I92P
Sprague
2364
CI4
033 I"F, 200 Y, 5'/( , Type 192P Sprague
2431
CI5
3-12 pF, Type 503-27 Erie
2535
CI6
.01I-'F, (-0+100) 6 me wI., Type BYA6S1 Cornell-Dubilier
2067 CI 7
12 I"F, 250 Y, Type BR-1225
Cornell-Dubilier
2508 CI8 6.2 pF, 5%, Type QC
Qualiry
2248
Cl9
18 pF, 500 Y, 5 0E , Type CM-15 Areo
2429 C20 7-45 pF, Type 503-27 Erie
2236 C21
200 pF, 500 Y, 5% , Type CM-15 Area
2371 C22 .047
I-'F, 200 Y, Jo q , Type 192P Sprague
275)
C23A 20 I-'F, 300 Y, Type DFP
Sprague
2753 C23B 20
I-'F, 3000 v, Type DFP
Sprague
275)
C23C
)0 I"F, 50 V, Type DFP
Sprague
2509 C24 1 pF,
10 %, Type QC
Quality
2370 C26 .2 2 I-'F, 400 Y, 10 % , Type
355E224K
Gudeman
C27 .S5
I-'F, 850 V (Supplied as parr of #3052, Tl) Sola
C27 1.0
I-'F, 850 Y (Supplied as parr of #3055, Tl) Sola
2754
C28A 1,000 I"F, 25 Y, Type DFP Sprague
2754 C28B 1,000
I-'F, 25 Y, Type DFP
Sprague
2751 C29
80 I-'F, 300 V, Type DFP Sprague
2750
C30A 80 I-'F, 350 V, Type DFP
Sprague
2750 OOB
20 I-'F, 350 Y, Type DFP Sprague
2370 C31 .22
I-'F, 400 Y, 109'(, Type 355E224K Gucieman
22 28 C32 50 pF, 500 Y, 5 S:L Type CM-15 Areo
2256 C33 500 pF, 500 Y, W
eE- , Type DM-15 Areo
2354
C)4
.15 I-'F, 200 Y, Type 192P Sprague
2354 C35
15 I-'F, 200 Y, Type 192P Sprague
-
15 -