Tektronix 434, Инструкция по эксплуатации

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Circuit Description—434
stage. The adjustm ent o f R817 determ ines overall h o ri­
zontal a m p lifie r gain. Pressing the LO C A TE b u tto n applies
— 15 volts to the base o f Q825B through R95 and R 811.
T his provides a small am ount o f p o sitio nin g o f the display
in the d ire c tio n o f the non-store pre-view area to aid in
locating display p rio r to storing a single-sweep. The o u tp u t
signals fro m the co lle cto rs o f Q 8 2 5 A and Q825B are
applied to the bases o f e m itte r fo llo w e rs Q 8 3 0 A and
Q830B respectively.
Signal L im itin g Push-Pull A m p lifie r
Q 835 and Q 836 fo rm a push-pull a m p lifie r stage w ith
Q 835A and Q 836A com prising a cascade a m p lifie r in one
side and Q835B and Q836B a cascade a m p lifie r in the other
side. Sweep m a g n ifica tio n is accomplished by m o d ify in g
the gain setting resistance between the em itters o f Q 8 3 5 A
and Q 835B. C R 835 and C R 865 lim it the difference in
signal am p litu d e between the bases o f e m itte r fo llo w e rs
Q 836A and Q 836B . This prevents a m p lifie r over-drive when
the sweep is m agnified or positioned to one extrem e or the
o th e r. CR836 and C R866 provide a d d ition a l overdrive
p ro te c tio n .
Q861 is a re la tive ly co nstant cu rre n t source fo r Q 835
and Q 836. When the B EA M F IN D E R pu sh -b u tto n is
pushed the c u rre n t through Q861 is reduced by a p p ro x i­
m ately tw o m illiam peres. This reduces the d ynam ic range
o f the signal lim itin g push-pull a m p lifie r stage, thereby
lim itin g the trace to w ith in the CRT graticule area. The
M a g n ifie r R egistration a d justm ent R 868 balances the
quiescent DC c u rre n t to the bases o f Q 870 and Q 880 so a
centerscreen display does n o t change po sitio n when the
sweep is m agnified.
O u tp u t A m p lifie r
The push-pull o u tp u t o f the Signal L im itin g Push-Pull
A m p lifie r stage is connected to the O u tp u t A m p lifie r
th ro u g h C R870 and C R880. Each h a lf o f the O u tp u t
A m p lifie r can be considered as a single-ended feedback
a m p lifie r w h ich am plifies the signal cu rre n t at the in p u t to
produce a voltage o u tp u t to drive the h o rizo n ta l d e fle ctio n
plates o f the C RT. The a m plifiers have a low in p u t
impedance and require very little voltage change at the
in p u t to produce the desired o u tp u t change.
Q 895 is a re la tive ly constant voltage source. The base o f
Q 895 is biased to set the e m itte r at a p p ro xim a te ly +5 volts
and the anode o f C R 898 a t a p p ro xim a te ly +6.5 volts. T his
sets the base o f Q 880 and the base o f Q 870 very near the
same quiescent DC level. C R 870 and CR880 become back
biased and are tu rn e d o ff when overdrive in the positive
d ire c tio n occurs at th e ir cathodes.
Transistors Q 870 and Q 880 are inverting am p lifie rs
whose c o lle c to r signals drive the em itters o f com plem entary
am p lifie rs Q 874-Q 877 and Q 884-Q887 respectively. The
o u tp u t signal fro m com plem entary a m p lifie r Q874-Q 877
drives the le ft h o riz o n ta l d e fle c tio n plate o f the C R T, and
th e o u t p u t s ig n a l
f r o m c o m p le m e n ta ry a m p lifie r
Q884-Q 887 drives the rig h t h o rizo n ta l d e fle c tio n plate.
C871 and C881 adjust the tra n sie n t response o f the
a m p lifie r so it has good lin e a rity at fast sweep rates.
POWER SUPPLY P R IM A R Y
General
The Power S upply P rim ary c irc u it provides c o n tro lle d
drive to the p rim a ry o f pow er transform er T 1 0 8 5 to
achieve m ore e ffic ie n t generation o f secondary voltages.
This c irc u it also contains the c irc u itry necessary to regulate
the secondary voltages against change due to variations in
in p u t line voltage o r frequency, or changes in pow er supply
load. Figure 3-13 shows a detailed b lo ck diagram o f the
Power S upply P rim ary c irc u it. A schematic o f this c irc u it is
shown on diagram 9 at the rear o f th is manual.
Line In p u t
Power is applied to this c irc u it through Line Fuse
F I 0 0 0 , R 1002, T herm al C u to u t S1002, Line F ilte r
F L 1 0 1 0 , and POWER sw itch S1Q10. Resistor R 1002 lim its
the am p litu d e o f surge currents at in stru m e n t tu rn -o n .
Therm al c u to u t S1002 provides therm al p ro te c tio n fo r the
in stru m e n t. If the internal tem perature o f the instrum ent
exceeds a safe operating level, S1002 opens to in te rru p t the
applied pow er. When the tem perature returns to a safe
level, S I 002 closes to re-apply the pow er.
The Line F ilte r made up o f C 1004, C l 006, L I 004,
R 1004, and T 1 0 0 4 is designed p rim a rily to suppress the
2 5 -k ilo h e rtz interference originating w ith in the pow er
supply. L I 004 provides d iffe re n tia l and com m on-m ode
in d u c ta n c e ; T 1 0 0 4 provides a d ditional com m on-m ode
inductance. Com m on-m ode filte rin g is provided by C l 005
and C l 006 along w ith the com m on-m ode inductance of
T 1 0 0 4 . R 1004 provides com m on-m ode dam ping fo r
C 10 0 4 -C 10 0 6 -T 1004.
When the POWER sw itch S1010 is closed, line voltage is
applied to the p rim a ry o f transform er T 1 1 1 5 and to the
full-w ave b rid g e -re ctifie r C R 1016. T 1 115 provides a sample
o f the AC line-voltage to the Trigger Generator c irc u it fo r
o peration in the L IN E triggering mode. C R 1016 rectifies
the AC line voltage in to a DC voltage to be used in the
Power Supply P rim ary c irc u it. C l 016 provides a measure o f
filte rin g to the rem aining AC com ponent. R 1016 discharges
C 1016 w hen in stru m e n t power is turned o ff. T ransform er
T 1 0 3 6 provides a d d ition a l 2 5 -k ilo h e rtz filte rin g .
3-18