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Sect.IV
Page 14
5) Repeat steps 1 through 4 on the other bands.
On the highest frequency band adjust the slug with
a plastic allen wrench (#8).
If any
adjustment
is necessary check maximum
oscillator current as in paragraph 4-15.
6) Connect
the probe
of an
oscilloscope to the
cathode of CR3, This point can be found on the pink-
white wire between the amplifier stator turret ter-
minal block and the tie-point for the 33K resistor
R25,
7) Set the MODULATION
SELECTOR to EXT. DC,
8) Connect a square-wave
generator, such as the
@ Model 211A
set to 1 KC to the MODULATION
INPUT-OUTPUT
connector.
Feed
in sufficient
square-wave
signal so that the carrier is cut-off
for at least part of the cycle.
9) Tune throughout all bands and check the pattern
on the oscilloscope for ringing or squegging.
Re-
duce the frequency of the external modulation
to
300 cps on the lowest frequency band to keep from
overmodulating.
If ringing is found, remove
the
shield to retune the amplifier. See paragraph 4-2
for instructions to remove this shield.
10) Measure
the RF Amplifier plate current with
@ Model 428A Clip-On Milliammeter clipped over
the red-green lead going to the 100 ohm resistor
R15
on
the turret stator contact terminal block
(beneath RF Amplifier chassis).
If a Model 428A
is
not available, unsolder the red-green lead on
the B+ side and insert a conventional 300 ma milli-
ammeter,
By-pass the point between the 100 ohm
resistor and the meter with a 0.1 mfd capacitor.
11) Tune the inner slug in the amplifier coil from
the
top for a plate current dip at the low end of
one band.
12) Tune the trimmer capacitor fora plate current
dip at the high end of the same band.
This adjust-
ment is made through a hole inthe chassis between
V3
and V4 underneath
the amplifier
turret shaft.
Use a plastic screwdriver for this adjustment.
In
addition, if this tool has a metal tip, slide a tiny
piece of tubing over the metal tip to prevent the
trimmer
shorting
to ground
when
making
this
adjustment.
13)
Recheck ringing as in step 9.
14)
Repeat steps 9-13 on all bands.
Model 606A
4-15
SET
MAXIMUM
OSCILLATOR
CURRENT
Set MODULATION
SELECTOR-
- - - - - - CW
RANGE
---+-+--+----
19 MC-65 MC
1) Measure
RF Oscillator plate current with
@
Model
428A
Clip-On
Milliammeter
clipped over
red-green
lead going to the 100 ohm resistor R9
on
turret
stator contact terminal
block (beneath
oscillator chassis). Ifa Model 428A is not available,
unsolder the red-green lead on the B+ sideand in-
sert
a conventional
300 ma milliammeter.
By-
pass the point between the 100o0hm resistor and the
meter with a 0.1 mfd capacitor.
2) Tune
FREQUENCY
dial throughout the 19 MC-
65 MC band while noting the current.
3) Adjust Osc, Level control (R3) on the oscillator
chassis
for
a maximum
current of 25 ma
atthe
frequency of maximum current.
If this
adjustment is made,
check the following:
- Paragraph 4-16, Carrier Zero Set
- Paragraph
4-17,
Maximum
Carrier
Set and
Modulation Zero Set
- Paragraph 4-18, Set Percentage Modulation
Meter
4-16
CARRIER
ZERO
SET
Set RANGE
- ----+-+----
50 KC - 170 KC
ATTENUATOR
- - + ---+----
1 VOLT
ATTENUATION
VERNIER-
=
- - - fully ccw
Carrier
Output Zero (R35)
- - - - fully ccw
MOD, SELECTOR - - -
EXT DC with no input
MODULATION
VERNIER
- - - = - fully ccw
1) Connect
oscilloscope
to output
of the Output
Termination.
2) Zero-Set the carrier output meter with the in-
strument off as explained in paragraph 4-9,
3) Turn on and allow 5 minutes warm-up.
4) Slowly turn Carrier Zero Set control (R35) on
the RF
Amplifier
chassis clockwise until there is
some
output
on the oscilloscope.
Then
adjust
Carrier Zero Set until the indication on the oscil1-
loscope,
set
to the
most
sensitive
range,
just
collapses.
Set the sweep
on the oscilloscope for
a free-running condition so that the indication will
not disappear
for lack
of synchronizing signal.
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