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Set
the signal
generator
to
exactly 4)) kc and adjust iron cores
in
T4
and T6
for maximwn
output.
The
o,·craJJ sensitivity
of the
i,f ampli6er can
now be measured and should be 70 microvolts for
rn
milliwatts out, if the
signal generator fs «liable and the output meter matched to the output
transformer, i.e., approximately 17,000 ohms. The selecti-,ity of
the
i•f channel
should be
such that signals are 40 db
down,
at 14
kilocycleJ
of! reJonancc.
For checking purposes
the high
side of the
signal
generator may be
tr1nsfcrred
to
the
grid
of
the IP)GT/G i,f ampli6cr. Hert an input
of
4)00
microvolts should give
an output
reading of 10 milliwatts.
After the
,.( ampli6er
has been
accurately
adjusted,
the
PHONE.(.W
,,.·itch should
be
turned
to c-w
and the
core in the BFO transformer T)
ad;ust<d
to gh·c a
1000 cycle
bdt with the i-f signd. This
.
can best
be
adiusud
by
taking the modula11on off the i-f signal from the signal generator.
The r-f
detector and oscillator circuits may be adiustcd now.
Connect
the high side
of the signal
generator to the antenna connector
through
a
100
uuf condenser and
the other
side
to
any convenient
point on
the chassi$.
Lea,·c
controls as
gi,·cn abovt but remove the short from the
gang
condenser.
·
Set the receiver dial and signal generator to ).8 megacycles modulated
30%
at
400
~Jes. Adjust the trimmer condensers C2, C4, and C9 for
maximum
output: these arc mounted on the gang condenser. Consideriblc
care must be
t.aken
in these adjustments to see that all three circoit.s arc in
tune.
It
will be found necessary lo rock the gang condenser back and forth
•cross the
signal when
adjusting
the antenna and detector trimmers C2 and
C4
rcspectiv,ly.
Now set
the
signal generator and receiver dial to a frequency
of
}.2 mega~les modulated 30% at 400 cycles and adjust the iron cores in
lransformm Tl, T2, and T; for maximum output.
The •bove
adjustmcnlJ
should be r<pcatcd until the correct adjustments
of the
com
do not affect the
correct
adjustments of the trimmer
condenscu.
Wh,n the receiver h>.s been correctly adjusted the ovcraU sensitivities
at ;.2. 4.6 and ).8 megacycles should be 4, ) and 6 microvolts respectively
for
10
milliwatts
out.
These 6gures will varr. however, depending on the
trpe of signal generator being used, so that ,f the sensitivities arc approx-
im,tely as
abo•e, the
re<:eiver
showd
be
considered
correctly
adjusted.
When replacing vah·es v.,hich arc used
in
any part of the receiver
circuit that has a tuning
adjusllncnt
associated with it-. that particular
adjustment should
be checked
foi
maximum s,nsitivity. Thi, may
be
done
without a
si,gml
~ncr.toc
by
adjusting
for maximum noise lc\·c1. However,
the use of a signal gener,tor is strongly recommended when at all possible.
When the IA 7GT/G
converter
valve is changed it is necessary to trim
the receiver at ) 8 megacycles, as previously outlin<d, to compensate for
vui1tions
in
valve
capacities.
13
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