Operating instructions

52,
First
R-f
Amplifier
Vl
(figs.
24
and
43)
The first
r-f
amplifier
covers
the
tuning
range
of the
receiver
in
four
bands.
In
the following
anal;rsig,
the band
1
circuits
(1.5
to 2.7
mc)
are discussed
in
complete
detail.
The
analyses
of
bands 2,
3, and
4
are
concerneil
onl1,
with
the circuit
variations
that
are accomplished
by
band
srvitching.
a.
The
signals
picked
up by
the
antenna
are
developed
across
the
primary
u'inding
of trans-
former
T1
(fig.
a3).
Contacts
on PHN.-C.W.-
NET-CAL.
srvitch
S2
(section
2, rear)
and
BAND
SW. su'itch
51
(section
2,
rear)
couple
the
antenna
to
the
transformer
winding.
Neon
tube E2
protects
the
transformer
primary
rvinding
from
overload.
The
primary
of
T1 is
shunted
by a
7\-ppf
(micromicrofarad)
capaci-
tor connected
internally
within
the
transformer
assembly.
b.
The
secondary
rvinding
of
transformer
T1
is
tuned
by
one section
of the MANUAL-PRE-
SET TUNING
capacitor,
C1A,
and
At{T.
TRIIII{ER
C2
(fie.
aB).
Section
3, rear,
of
the BAND
SW. stvitch
connects
the capacitors
ircross
the ri'incling.
The
tunecl
circuit is
coupled
to the
g'rid (pin
6) of V1 through
capacitor
CB.
Resistor
R1 and
avc
circuit
pr:ovicle
a
d-c re-
:.iln
for
the
gricl
circuit.
Capacitor
C11 is
a
part
of
the avc fiìter
circuit.
While
bancl 1
is
in
Lrse. another
section
of
the
BA\ID
SV/.
sri'itch
(section
3, front)
grounds
the
secon-
rlaries
of all
antenna
coils
not in
use-in
this
case,
u'iucling
C of T1
and B
and D rvindines
of T5
(fig.
24).
c. The
first
r-f
amplifier
utilizes
a
1L4
pen-
tocle tube
(fig.
43).
Filament
voltage for
the
tube is
obtained from
the
l.4-volt
d-c
potential
at
pin
11
of J4.
Screen voltage
is
suppiied
from
the arm of R.F.
GAIN control
R32
through
r-oltage-droppinC
resistor
R2
and
section
3,
rear,
of function
switch
52.
The
gain
control
is
cor.rnected across the 90-volt
potential
present
ìretrveen
pin
6
of
J4 and
ground.
Capacitor
C49
l,r'ovicìes
noise filtering, and capacitor
C4
places
the
screen
at r-f
ground
potential.
Plate volt-
r,.!re
is obtained from
the 90-volt supply
through
r',.sistor
R3, the
primary
of T2
(u'incling
C)
:r,ì
section
4, front,
of
BAND
SW. switch 31.
lì sistor
R3 and capacitor
C5
form
a
plate-
r'eLrit
decoupling netu'ork.
d.
Tube \-1
antplifies
the
antenna
signals and
develops
the
amltìified signal
across
the
nn-
tuned
primar'1'
of T2
(ri'incling
C).
The
signal
is
coupled
incluctit-el1-
to
the tunecl
seconclary
r.vinding
in
the
gricl
cii'cLrit
of
second
r-f
ampli-
fier
V2.
C10
coupÌes the
signril
from
the
sec-
ondary
winding
of T2
to the contxrl
grid
of V2.
e.
When BAND
S\trr.
sl-itch
31
is
pìacerl
in
the
band 2
position,
the f ollori-ing
circuit
changes
are
effected
to allou'
corelage
of the
2.7-
to 5-mc
band
(frs.
2a).
(1)
Section 2,
reay,
and section
3,
r'ear,
select
the
C
rvindings
of T1 in
place
of
the B rvindings
as the
anteuna
coij.
(2)
Section
3,
front,
removes
the
gr.onncl
from
the
C
rvinding
of T1,
ancl
places
a
ground
on the B r.vinding.
(3)
Section 4 selects
the D
section
of T2,
in
place
of
the
C
section,
as the
plate
load
for
V1.
/.
When BAND
SW. srvitch
is
placecl
in band
3
position
(fig.2a),
coverage
of the 5- to 9.b-mc
band
is
provided
through
circuit
changes
sim-
iliar
to those
detailecl
for
band 2. When
srvitch
51
is
set to band
3, sections
2,
rear,
and 4, front,
select
the
B r.r,inclings
of
T5
ancì the D rvinclings
of T6
as
antenna
coil and
V1
plate
load, r-espec-
tively.
Section 3. front,
of the srvitch
gronncls
the
unusecl secondaries
of
the antenna
trans-
formers.
A
25-t,t,f
capacitor
is in
shunt
rvith
the
primarv
of
the antenna
coil.
.9.
When BAND
SW. su'itch
is in
bancl4
posi-
tion
(fig.
24),
x.'indings
D
of T5
ancl
r.inding
E
of T6 are
selected
to
provide
coverage
of
the
9.5-
to
1S-mc
bancl. A 2,400-pp.f
capacitor
(in
series rvith
the seconclan
of T5)
is
usecl as
a
padcler
to
provicìe
proper
tracking.
/i.
Function
su,itch
32,
section
2,
rear
(fig.
43),
connects
the antenna
to
transformer
T1
or
T5 in
the PHN.
C.W.,
and NET
positions.
\\rhen
the
switch is
turned
to
CAL., section
2, rear,
grounds
the
antenna coil
and opens
the
antenria
circuit.
The
calibration
signaÌ
may
be sr-rpplierì
to
the r-f
amplifier
in
place
of the
antenna
sis-
nal
(par.
67).
53.
Second R-f Amplifier
V2
(figs.24
and 43)
The second
r-f
amplifief
co\-els
the
tuning
range
of the receiver
in
the
sanle
ntàìnner
as the
first
r-f
amplifier.
39