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TM 11-6660-204-25
creases resistance and a more negative voltage
itors have a low reactance to ripple frequencies
increases resistance. Control amplifier tube V410
and practically the entire voltage change appears
controls the amount of voltage supplied to the
across resistor R410. This voltage change either
grid of tube V409. The cathode of tube V410 is
adds to or subtracts from the grid voltage sup-
connected to a constant reference voltage, which
plied by potentiometer R412, so this circuit re-
is supplied from negative voltage reference tube
duces the 120-cycle ripple voltage as well as the
V411. Because the cathode voltage is held con-
changes due to line voltage or load conditions.
stant, only the grid voltage affects operation of
Capacitor C406 is the output filter capacitor.
this circuit. The grid voltage is supplied from a
c. The negative regulated power supply (fig.
bleeder network across the regulated negative 175
218) furnishes a constant negative 175 volts re-
volts determined by the position of the arm of
gardless of variations in the input voltage or load
potentiometer R434. When the line voltage in-
creases or the load current decreases, the voltage
across the bleeder increases. A portion of this
(1) Rectifier tube V408 functions as a con-
voltage change, determined by the setting of po-
ventional full-wave rectifier. This circuit is shown
tentiometer R434, is amplified by tube V410 and
as a block in figure 218; for individual compo-
applied as a negative swinging grid voltage to
nents, refer to figure FO6. Fuses F403 and F404
tube V409. This decrease of grid voltage causes an
are connected in series with the plate leads of
increase in the effective plate to cathode resist-
rectifier V408 for overload protection. Capacitors
ance and increases the voltage drop across tube
C415 and C416, with choke coil L402, comprise a
V409, This increase in voltage drop, which is al-
pi one-section filter for the unregulated supply.
most equal to the original voltage rise, returns the
Resistor R421 is a bleeder resistor which dis-
grid bias value of tube V410 to the original input.
charges the filter capacitors when the equipment
The action of the regulator is so rapid that it can
is turned off. The negative series regulator tube is
be considered to be instantaneous. Capacitor C418
a twin-triode type which obatins its plate voltage
provides a low reactance path to the grid of tube
from the unregulated supply, through parasitic
V410 for any rapid changing voltage or ripple
suppressors R424 and R425 in one plate circuit,
voltage. This voltage change either adds to or sub-
and parasitic suppressors R426 and R427 in the
tracts from the grid voltage supplied by poten-
other plate circuit, The cathode is returned to
tiometer R434, so this circuit tends to minimize
circuit ground. The negative 175 volts is obtained
ripple voltage in addition to rapid changes in line
from the center tap of the plate winding. Resis-
voltage or load conditions, Capacitor C420 is the
tors R428 and R429 are grid-current limiting re-
output filter capacitor and bypasses any hf volt-
sistors, A voltage divider which consists of resis-
age component.
tors R433 with potentiometer R434 is placed be-
tween the regulated negative 175-volt output and
d. A positive 500-volt unregulated voltage sup-
circuit ground. The voltage of potentiometer R434
ply is obtained by taking the unfiltered and unreg-
is applied to the control grid of negative control
ulated voltage from the filament of positive sup-
amplifier tube V410. The screen-grid voltage" for
ply rectifier tube V401. This voltage is applied
this tube is obtained from a voltage divider con-
through resistors R417 and R418 to the control
sisting of resistors R430 and R431 and the nega-
winding of balancing motor B501. Filtering is
tive voltage reference tube V411 to ground, con-
accomplished through capacitor C408 and the in-
nected across the regulated negative 175-volt sup-
herent inductance of the motor winding.
ply. The plate of tube V410 is directly connected
e. A filament burn-out neon indicator lamp
to the grids of tube V409 through grid-current
(E401) is provided for pen-lifter control tube
limiting resistors R428 and R429, and controls the
V407. This lamp is connected across the filament
operation of this series regulator tube. Negative
so it is normally short-circuited and does not indi-
voltage reference tube V411 is a cold cathode-type
cate until the tube filament opens. A similar indi-
gas voltage regulator tube, which normally oper-
cation is provided for tubes V305, V304, V309,
ates at 87 volts and is connected to the cathode of
V308, V306, and V307 in the signal converter cir-
tube V410 to provide a constant reference voltage
cuits by neon indicator lamps E301 through E306.
for comparison with the grid voltage of negative
control amplifier tube V410.
2-18. Frequency-Time Recorder
(2) Series regulator tube V409 functions as a
The purpose of the frequency-time recorder is to
variable series resistor, which is controlled by its
make a continuous record of the frequencies re-
grid bias voltage. A less negative grid voltage de-

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