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BOONTON
RADIO
CORPORATION
MAINTENANCE AND CALIBRATION
E. POWER
SUPPLY
ADJUSTMENT
Potentiometer R108 marked "+-260V ADJ" should
be set to produce 260V -- 10V at pin 3 or б of tube V14
(6AS7G).
Normally,
this control need be adjusted
only if tubes V15
or V16
(GAUG
and OB2)
аге re-
placed. If the OB2 has been replaced, it is desirable to
"age in" the tube for two or three hours of operation
before adjusting R108.
F. METER
RECALIBRATION
General
The Carrier Monitor Meter is essentially a dc volt-
meter,
used
to read the rise of dc voltage
at the
cathode of the follower caused by rectified carrier. The
Percent Modulation Meter functions as an ac vacuum
tube voltmeter reading the audio component
of the
carrier.
The calibration of both meters may be checked by
connecting calibrated "standard" meters to the Meter
Calib tip jacks.
Standard Meters required are as follows:
(a)
D.C. Voltmeter 0-50V, 100,000 ohms or more.
Calibrated
to be accurate
within
144% from
20 to 50V.
(b)
А.С.
Voltmeter
0-10V,
impedance
greater
than 100,000 ohms. Calibrated to be accurate
within 2% at 6.68 and 7.92V RMS at 90 cycles.
Calibration of the "Carrier Monitor" Meter
Connect the calibrated D.C. Voltmeter to the Meter
Calib tip jacks (J6 and ]7); turn the Carrier Switch
(S1)
to Off; and carefully zero the Carrier Monitor
meter
(M2), using its Zero control
(R56). Read the
D.C. meter (normal reading is approximately 27 volts).
Switch to КЕ, and set the Carrier Adjust control
(R13) for a reading on the D.C. voltmeter exactly 22
V. higher than that obtained in the preceding step.
Check the reading of the Carrier Monitor meter,
which should read red line. If it does not, adjust the
Mon Cal control (R54) to produce a red line reading.
Repeat the procedure to insure greatest accuracy.
Calibration of the "Percent Modulation" Meter
Connect the calibrated A.C. voltmeter to the Meter
Calib. tip jacks. Turn the Mod switch
(S5) to 90-
150 ~;
the DB Тие Ratio switch (S6), to Cal 90 — ;
the modulation
range switch
(S3)
to 0-50%,
and set
the Carrier Monitor meter to the red line.
Adjust the Mod Level control
(R1)
for a reading
of exactly 6.68 volts on the AC voltmeter. The Percent
Modulation meter should now read 42%. If necessary,
adjust the 5096 Cal control
(R40)
to produce a read-
ing of 42%.
Operate
the meter
range
switch
to the 0-100%
range, adjust the Mod Level control for a reading of
exactly 7.92 volts on the AC voltmeter and, if neces-
sary, adjust the 100% Cal control (R51) for a reading
of exactly 50% on the Percent Modulation meter.
*NOTE:
The 0-50% range must be calibrated be-
fore the 0-100% range.
Set-up of Mod Level Control Knob
Turn the Carrier switch (S1) to RF, the Mod Level
control
(R1)
full counterclockwise,
the Frequency
dial to 332.0 mc, the Mod switch
(S5) to the 90-150 —
position, the DB Tone Ratio switch (S6) to Cal 90 ~,
and set the Carrzer Monitor meter
(M2)
to the red line
using the Carrier Adjust control (R13). Turn the 90--
(R83),
150~
R84 and 1000 —
(R82)
controls
(lo-
cated behind
the panel door)
full clockwise.
Advance the Mod Level control until the Percent
Modulation
meter reads 46%
(with the meter range
switch
(S3)
in the 0-100%
position).
Switch
to Cal
150 —
and note the reading of the Percent Modula-
tion meter. If it is more than 46%, reduce to 46%; if it
is less than 42%, increase to 4206 using the Mod Level
control. The pointer of the Mod Level control knob
should be at the reference mark (vertical). If it is not,
loosen its set screws and reposition it to be so. Tighten
set screws and check to be sure the electrical setting of
the Mod Level control has not been disturbed.
With the DB Tone Ratio switch at the Cal 90 ~
position, set the 90— control for a reading of exactly
40% on the Percent Modulation meter. Switch to Cal
150--- and similarly set the 150— control for a read-
ing of exactly 40%. Switch from the Cal 90—to the
Cal 150— position several times to be sure that the
Percent Modulation
meter reads 40% on each.
With the DB Tone Ratio switch in either the Cal
90 — ог the Cal 150— position, turn the Mod Level
control fully clockwise. The Percent Modulation meter
should read more than 100%.
a
es
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