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The output f r o m cathode follower V5 i s coupled by capacitor C12
to the output amplifier.
3 -4
OUTPUT AMPLIFIER
The output amplifier includes tubes V8 and V9. The signal incom-
ing f r o m the selective amplifier i s passed to the grid of V8 via
variable r e s i s t o r R57, the setting of which i s adjusted by the AM-
PLITUDE control on the control panel. Thus, by adjusting the in-
put to the output amplifier, the AMPLITUDE control becomes, in
effect, the gain control for the instrument.
Pentode V8 operates a s a driver for high-mu pentode V9, the power
output tube. Pentode V9 i s connected a s a triode to allow the tube
to work into very low impedance loads without generating appreci-
able distortion. Negative feedback f r o m V9, applied via capacitor
C19 and r e s i s t o r R67 to the cathode of V8, is used to minimize
distortion.
The output of V9 i s passed, via a rectifier-type voltmeter, an
attenuator, and a n impedance -matching transformer to the OUT
-
PUT binding posts.
3-5
VOLTMETER
The voltmeter circuit includes variable r e s i s t o r R69, a germanium
diode full-wave rectifier, and a one-milliampere meter connected
a c r o s s the rectifier bridge. Resistor R69 i s provided for adjust-
ment of the meter calibration. The m e t e r i s arranged to indicate
the output voltage directly in volts a c r o s s 600 ohms and in dbm,
with 0 dbm equal to 1 milliwatt into 600 ohms.
3 - 6
ATTENUATOR
The attenuator has three sections, each of which i s controlled by
i t s own dial. One section i s of an L-type configuration, with ten
steps o f . 1 db each. The other two sections a r e bridged-T configu-
rations, one of ten 1 db steps and the other of ten 10 db steps. The
three attenuators provide f r o m
.
1 db to 111 db attenuation of the
output voltage.
3-7
IMPEDANCE-MATCHING TRANSFORMER
Connections to impedance -matching transformer T2 a r e established
by the IMPEDANCE switch, S2. In the 50, 150, and 600 positions
of the switch: (1) the output voltage i s passed to the p r i m a r y winding
of transformer T2 and (2) the secondary of T2 i s connected to the
OUTPUT binding posts.
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