TM 11-662525514/TO 33A1-13-1701
produced by the voltage drop across R20, in the
and V10 controls the output of V8.
fixed resistive arm of the bridge (fig. 6-3). The
62. Preamplifier Circuit
output of V4 is obtained at the cathode. This out-
put is applied to the input of V2 as additional
negative feedback, and to the junction of the fixed
of the preamplifier circuit. Input signals to the
resistive arm and series reactive arm in the bridge
preamplifier circuit may be connected to AF IN-
circuit.
PUT binding posts E7 and E8, or to AF-RF IN-
PUT (TS-723A/U only) binding posts E5 and E6.
6-3. Wien Bridge Circuit
AF-RF selector switch S2 (TS-723A/U only) pro-
vides selective switching between the AF INPUT
of the bridge. The bridge circuit operates as a
binding posts and the AF-RF INPUT binding
variable-frequency rejection filter. It has a fixed
posts. When S2 is set to AF, the AF INPUT
resistive arm, a variable resistive arm, a series re-
binding posts are connected to the input of the
active arm, and a shunt reactive arm. The fixed
p r e a m p l i f i e r circuit through C6. AF INPUT
resistive arm consists of R20 and R21. The
binding posts E7 and E8 are used to connect
variable resistive arm consists of fixed resistors
audiofrequency signals.
R24, R25, and R22, and variable resistors R89
b. Tube V2 is the first voltage amplifier. Signal
INPUT control R4 is a variable resistor which ad-
a n d R23. Resistor R89 is the range setting
balancing chassis c o n t r o l which is adjusted
justs the level of the signal applied through C7 to
during alignment of the spectrum analyzer and
the grid of V2. Operating bias for V2 is obtained
does not normally require readjustment. Variable
from the voltage drop produced across R9. Resis-
resistor R23 is the BALANCE control which is
tor R8 is the grid return. Resistors R6 and R7,
adjustable from the front panel.
and variable resistor R5 (NOISE GAIN) deter-
b. Resistors R1, R26, R3, R27, R39, and R28
mine the amount of negative feedback returned to
V2 from the output of bridge amplifier tube V6.
are connected by frequency RANGE switch S3 in
pairs according to the frequency range selected.
Resistors R6 and R5 are switched in or out of the
These resistors form a part of the series reactive
circuit by section S4B of function switch S4.
arm. For the X1 frequency range, R1 and R26
When these resistors are switched out of the cir-
form the series resistance for the arm. For the X10
cuit, R7 and R9 form a divider network for the
frequency range, R3 and R27 form the series
negative feedback voltage. The resultant gain of
resistance for the arm. For the X100 frequency
the combined preamplifier and bridge amplifier
range, R39 and R28 form the series resistance for
circuits is 20 dB. When R5 and R6 are switched
into the circuit, they form a divider network, in
the arm. Variable FREQUENCY tuning capacitor
C13 is a four-section tuning capacitor. Capacitor
combination with R7 and R9, which adjusts the
C13A and C13B are parallel-connected in the
overall gain of the preamplifier and bridge ampli-
fier circuits to 40 dB. Resistor R5 is used to adjust
series reactive arm. Capacitor C13C and C13D are
the overall gain of the preamplifier and bridge
parallel-connected in the shunt reactive arm of the
amplifier at 40 dB. This control is adjusted during
bridge. Trimmer capacitor C12 provides a vernier
c a l i b r a t i o n and alignment of the spectrum
tuning adjustment of the series reactive arm of
analyzer and does not normally require readjust-
the bridge to calibrate the FREQUENCY tuning
ment. Resistor R10 is the plate load for V2. The
dial. Fixed capacitor C14 compensates for the ef-
screen voltage of V2 is reduced by voltage divider
fect of the input capacitance of V5 in the bridge
R11 and R12. Resistors R13 and R90 provide a
amplifier circuit.
negative feedback path between the cathodes of
c. Resistors R47, R29, R91, R30, R2, and R31
V2 and V4. The output of the V2 is coupled to V3
are connected by switch S3 in pairs according to
through C8.
the frequency range selected. These resistors form
c. Tube V3 is the second voltage amplifier. Op-
a part of the shunt reactive arm of the bridge. For
erating bias is produced by the voltage drop
the X1 setting of switch S3, resistors R2 and R31
across R15. Resistor R14 is the grid return.
are connected to form a series resistance for the
Screen grid voltage is provided by voltage divider
shunt reactive arm. For the X10 setting of S3,
R16 and R18. Resistor R17 is the plate load for
R30 and R91 are connected to form a series resist-
V3. The output of V3 is coupled to V4 through
ante for the arm. For the X100 setting of S3, R29
and R47 are connected to form a series resistance
Cl0.
for the arm.
d. Tube V4 is the third amplifier stage and op-
erates as a cathode follower. Resistor R 19 is the
d. Variable FREQUENCY tuning capacitor
grid return for this stage. Operating bias is
C13 is mechanically controlled by two front panel
6-2
