Tektronix 543B, Instruction Manual

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Circuit Description — Type 543B/RM543B
activates K601 the series-string filaments have reached
operating tempera ture. When K601 is activated by K600,
relay contacts K601-3 shift the series-string filaments to the
regulated output of the + 100-volt supply.
The reference voltage source is the regulated output of
the -150-volt supply. V664 is the error amplifier, and
V677A is the series regulator tube. The error-feedback
circuit is trough R650 and R651, the junction of which is
connected to t he grid of V664. The top end of R650 is
connected to the regulated +100-volt output and the lower
end of R6 51 is connected to the output of the regulated
—150-volt supply to obtain reference voltage. With norma!
line voltages and loads, the voltage at the junction of R650
and R651 is about —1.7 volts with reference to ground;
this is the operating bias of V664.
If the load current, output voltage, or the input voltage
changes (incuding changes due to ripple), the output of the
reg100-volr supply starts to change also, but any
change appears across R650 and R651 and is applied to the
grid of V664 as a change in operating bias. Assuming that
the output of the reg100-volt supply tries to de-
crease, the reduced voltage at the top end of R650 permits
the voltage at the junction of R650 and R651 to go more
negative than the normal —1.7-volt level at that point.
The i ncrease in negative bias on the grid of V664 reduces
the flow of plate current through V664, the voltage drop
across plate-load resistor R663 decreases, and the plate
voltage of V664 and the grid bias of V677A go more posi-
rive. As the grid of V677A goes more positive, the resistance
that V677A offers to the flow of current is decreased and
the output voltage rises, compensating for the drop in output
voltage which initiated regulating action. Of course, the
regulator circuit can never completely compensate for a
change in output voltage, for there must be an error input
for the circuit to operate, but any error in output is reduced
by a factor equal to the loop gain of the regulator circuit.
The screen grid of V664 is used as a signal grid for in­
jecting a sample of any rippie or transient voltage present
in the unregulated side of the +100-voit supply into the
regulator circuit. The regulator circuit thereby becomes a
dynamic filter for ripple reduction. The ripple signal is
applied to the screen of V664, amplified and inverted in
phase by V664, then applied to the grid of V677A. By the
time the amplified and inverted ripple gets to the grid of
V677A, it is of proper amplitude and phase to ccncel out
the ripple appearing at the plate of V677A.
Unregulated +325-Volt Supply.
The unregulated +325-
volt supply voltage source differs somewhat from the voltage
source for the —150- and +100-volt supplies. A center­
tapped secondary on T601 (pins 5, 7, 10, and 14) and silicon
diodes D702 and D732 form a center-tapped bridge rectifier
circuit with the negative side connected to the positive un­
regulated side of the voltage source for the +100-volt
supply. The unreg325-voit output is taken from the
transformer center-tap (pins 7 and 10) connection.
The unregulated output of the voltage source for the
+100-volt supply is approxi180 volts. The unreg­
ulated output of the center-tapped bridge circuit is approx­
imately + 290 volts; this added to the unregulated —180
volts provides the +470 volts. However, for the unregulated
+350-volt output, the connection is made at the cerner tap
(+145 volts) of the bridge (the midpoint of the +290 volts).
Adding the +180 and +145 volts provides the desired out­
put of +325 volts.
+225-Volt Supply.
The voltage source for the regulated
+225-volt supply is the unreg325-volt supply
described in the preceding paragraphs. The regulator circuit
is similar to the regulator circuit found in the —150-volt
supply; the main difference being that instead of using a
glow discharge tube as a reference voltage source, the
reference voltage is from the —150-volt supply. The error
signal is picked off the junction of precision resistors R680
and R681. The upper end of R680 is connected to the +225-
volt output, and the lower end of R681 is connected to the
regulated —150-volt supply. The voltage at the junction
between R680 and R681 is approximately 0.1 volt which is
applied through R682 and R683 to the grid of V684B. The
cathodes of V684 are longtailed to the —150-volt supply
through R685. The grid of V684A is grounded. The error
signal is fed from the grid of V684B through the common­
cathode circuit to the A side of the tube. Notice that this
comparator is somewhat different from the comparator
used in the —150-volt supply; the output is taken from the
A side. The error signal is amplified by V684 and fed,
unchanged and in phase, to the voltage divider in the grid
of V694. V694 also amplifies and inverts the error signal
and applies it out of phase with any change in the +225-
volt output, to the grids of series regulators V677B and
V737B.
Here again, the screen of the error amplifier is acting as
an injection grid for ripple reduction. A sample of the
unregulated supply ripple is applied to the screen of V694.
V694 amplifies the ripple, inverts it in phase, and applies it
to the grids of series regulators V677B and V737B. The
result is that the same ripple appears simultaneously on the
grids and plates of V677B and V737B, but 180° out of
phase,- thus the ripple cancels out.
+350-Volt Supply. The input to the +350-volt supply is
t he full voltage output of the center-tapped bridge (see
description of unreg325-volt supply) added to the
unregulated side of the +100-volt supply. The operation of
the regulator circuit is very similar to the operation of the
-100-volt regulator except for different component values.
+ 500-Volt Supply. Rectified voltage from terminals 20
and 21 of T601 via D762 is added to the regulated voltage
of the +350-voit supply to supply the necessary voltage for
the +500-volt supply. The operation of the regulator circuit
is similar to that of the +100-vo!t regulator except for dif­
ferent component values.
Crt Circuit
The crt circuit (sec Crt schematic diagram) includes the
crt, the high-voltage power supply, and the controls neces­
sary to focus and orient the display. The crt (Tektronix Type
T5470-31 -2) is an aluminized, 5-inch, flat-faced, glass crt
with a helical post-accelerator and electrostatic focus and
deflection. The crt circuit provides connections for externally
modu'ating the crt cathode. The high-voltage power supply
is composed of a dc-to-50-kc power converter, a voltage
regulator circuit, and three high-voltage outputs. Front-panel
controls in the crt circuit adjust the trace rotation (screw­
driver adjustment), intensity, focus, and astigmatism. In­
ternal controls adjust the geometry and high-voltage output
level.
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