Tektronix 7704A User Manual

L eft Out put Am p lifier
Transistors Q4325, Q4351, Q4356,Q4371, and Q4381
are connecte d as α current-d riven fee d bac k amplifier . T he
input current is converted to α voltage out p ut signal to
drive t he left h orizontal deflection plate of t he C RT . Input
transistor Q4325, an ΝΡΝ transistor, res pon d s b est to
positive-goi ng input signals .
T
h e signal at t he collector of
Q4325 is connected to t
h
e emitters of output transistors
Q4356-Q4371 t h roug h two parallel path s .
H
ig
h -fre q uency
signals are connected t
h roug h
capacitor
C4325
.
L ow-
fre q
uency signals are connecte d
to t
h e output transistors
t
h
roug
h R 4324-Q4351- R4354 . T h e
output transistors
Q4356 an d Q4371 are
connecte
d
in
t
h e complementary
configuration to p rovi d
e
less
resistive
loa d
ing
at t
he
output .
T h e outp
u
t signal at t h
e
collector of Q4356-Q4371 is
connected to t h e left deflectio n p late of t
h
e C
R T
t
h
roug
h
R
4375 .
N egative fee db ack is p r ovi ded from t he collectors of
Q4356-Q4371 to t h e base of Q4325 t h roug h fee d bac k
networ k R 4374-C4374-Q4381- R 4329-C4329 . E mitter
follower Q4381 in t h e fee d bac k n etwor k provides current
gain for t he feedback signal . Wit h t h is configuratio n , t
h
e
inp u
t impe d ance of t
h e L eft
Output
Amplifier is low since
t he feedbac
k
networ k b eyo nd t h e emitter followers is
effectively re du ced in impe d ance as far as t he input signal is
con cerne d . V ariable capacitor C4374 a d j usts t
he transient
res p onse of t he feedbac k networ k to
provi de good linearity
at fast sweep rates . C4385-
R4385 provide ad j ustment for
correct h ig h -fre
q ue
n
cy gain versus fre q uency response in
t he amplifier .
R ig h t Output Am p lifier
B asic operation of t he Righ t O utput Amplifier stage is
t h e same as j ust descri b e d for t he L eft Out put Am p lifier
stage . N otice t hat t h e input transistor in t
h
is stage is
complementary to t h e corresponding transistor in t
h e L eft
Out put Amplifier stage .
T h erefore,
t
h
is stage
provid es t h e
best res p onse to
negative-going inp u
t
signals
.
C4391 pro-
vides linearity
a
d j ustment for t he Rig h t Output Amplifier
at fast swee p rates . T he output signal at t h e collectors of
Q4366-04395 is connecte d to t he rig h t d eflection plate of
t h e CR T t h ro ugh R4393 .
T hermal Balance N etwor k
Q4346 provi des t h ermal balance for t h e H orizontal
Amplifier circ u it . T he T h ermal Balance ad j ustment R4346
sets t he bias on Q4346 an d t h ere b y d etermines t h e
operating voltage for Q4325-Q4335 . T h is a dj ustment
com pensates for DC s h ift in t he CR T display to re d uce
low-frequency signal cross tal k . Dio de CR4348 provi d es
reverse-voltage b rea kd own p rotection for Q4346 w h en t he
instrument is first turne d on . Dio d es C R4346 and CR4344
establis
h
t
h
e operating b ias for Q4325-Q4335 .
+150- V olt Supp ly
Circu it
Description -7704A
Service
CR
T
CI
RC U IT
T he C R T Ci r c u it p rovi des t he control circ u its and t h e
h
ig
h
-voltage
poten tials necessary for the op eration of t h e
cat
h
ode-ray tube (C
R T) . T h is circuit i n clu d es t he Ζ -Axis
Amplifier stage to set t h e intensity of t h e CR T d isplay and
t h e A u to- F ocus Am p lifier stage to maintain o p
timum focu s
of t he C
R T
dis p lay .
T h
e
CR T Circ u it also contains t h e
Graticule- L ig
h
t
Su pply . F igure 2-48 s h ows α d etaile db lock
diagram
of t he C RT Circuit .
H ig h - V oltage
Transformer
T he H ig h - V oltage
Transfo r mer, Τ 4201, is driven by t he
20- k ilo h ertz s qu are-wave
voltage from t h e Inverter/
Rectifiers circuit (secondary
of L ow- V oltage Transformer
Τ 3101 on d iagram 8) . F
our secondary windings on
Τ 4201
provi d
e power for t he Graticu le- L ig h t S
up ply, +150- V olt
Su pp ly, CRT h eater voltage, A nod
e
V oltage
Mu lti p lier, and
t
h e C R T-Cat h od e Supply .
T
h e s q
uare-wave output of
Τ 4201 also d rives t h e Control-G r id
DC Restorer and
Focus-Grid DC Restorer stages t
h
roug
h R4217 and R4214
respectively .
T h e +150- V olt Su p
ply provi d es α semi-reg u late d voltage
for use in several
circuits in t h e 7704 Α (semi-regulation
is
ach ieve d by
Inverter Regulator ; see Inverter/
R ectifiers
description for
f u
rt
h er information)
.
B ridge rectifier
C R 4201-C R 4202-C R 4203-C
R4204 rectifies t he voltage
from t he secon dary of
Τ 4201 . R4201-C4201
filter
t
h e
rectified voltage
.
Graticule- L ig ht Su pp ly
T h e graticule lig
h
ts
DS5001-DS5002-DS5003 are
powere d by t h e Gratic
u
le- L ig h t Su p
ply Q4250-04254 .
Rectifie d voltage for t h is supply is provid e d by
CR4250
from α secon dary win d ing of
Τ
4201 .
T h e setti ng of t h e
front- p anel G R AT
I
LLUM control
R5000 determi n es t h e
bias on t h e b ase of
Q4254 . T h e level on t h e collector of
Q4254 t
h en determines t h e current th roug h Q4250 an d t h e
graticule lig h
ts .
Cathod e-Su pp ly R egulator
Α sam p le of t he o
u
tput of
t he C R T-Cat h o de S u pply is
connecte d to t h
e
Cat
h ode-Supply Regulator stage t h roug h
d
ivi
d
er R4123- R 4240- R 4241 . F ast ch anges of t
h
e cat
h
o d
e-
su pp ly output are couple d to t
h e
Cat
h
o
d e-Sup p ly Reg u -
lator t h roug
h R 4244-C4244 . U 4110 is connected as an
error am p lifier to sense any
ch ange in t he voltage level at its
non-inverting input (pin 3) .
T h e +50- V olt Su p ply, con n ec-
ted to R4123,and t
h e grou nd connecte d to p in 2- U 4110
t h roug
h R4120 p rovi d e t h e reference for t h is stage . H ig h
V
oltage
a d j ustment R4123 sets t he quiescent level at p in
3- U 4110 for α -2 .96- k ilovolt operating potential at t
he
2- 5 9

Tektronix 7704A Specifications

General

Brand	Tektronix
Model	7704A
Category	Test Equipment
Language	English