Operating instructions

Screen
voltage is
supplied
from
the 90-volt
d-c
potential
at
pin
6
of
J4, through
voltage-drop-
ping
resistor
R25
and
OUTPUT
HIGH-LOW
sx'itch
54
(in
HIGH
position).
Capacitor
C3g
places
the
screen
at
a-f
ground
potential.
plate
r.'oltage
is
supplied
from
pin
6
of
J4
thlough
a
portion
of
the u'inding
of T14
and
OUTpUT
HIGH-LOW
srvitch
54.
Capacitor
CB6
is
an
h-f a-f
fiÌter.
c.
The
signals
are
amplified
by
the
tube,
ancl
the output
is inductively
coupled
from
a
por-
tion
of the
primary
of T14
to the
secondary
of
T14,
thence
to the
PHONES
connectors
and
the
loudspeaker.
d.
In
the HIGH
operation
of
OUTPUT
HIGH-LOW
su'itch
S4, B+
voltage
(90
volts
dc) is
connected
directly
to the
plate
of lolv
a-f
amplifier
V7,
rvith
a-f bypass
capacitor
C3T
connected
from
plate
to
ground.
This
effective-
ly cancels
any
output
signal
from
VZ.
e.
DIAL
LIGHT
sr,vitch
SB can
be used
to
illuminate
dial light
E1 rvhen
required,
but re-
duces
the output
of tube
V8
by removing
the
filament
voltage
from
half
of
the filament.
62.
Beot-frequency
Oscillofor,
Port
of
V7
(fig.30)
The
bfo is
operative in
aÌl
positions
of PHN.-
C.W.-NET-CAL.
switch
32,
except PHN.
The
filament
and first
two
grids
of
Y7 are
used in
the bfo
circuit.
a. The
oscillator is
a self-sustaining,
series-
fed
Hartley
oscillator
operating
at
a
fundamen-
tal
frequency
of
151.66
kc
-+-1
to
1.167
kc.
The
third harmonic
(455
kc
-+3.5
kc) is
coupled
to
the
grid (pin
6)
of second i-f
amplifier
tube
V5.
The circuit
is
tuned by T13, the
capacitor
(535
ppf) connected in
the assembly
and
capacitor
C43.
Capacitor
C44
(B.F.O.
trimmer)
is used
to vary the frequency
of the bfo
and
produce
the beat note
for
the audio section
of
the
receiver.
b.
The
75-ppf capacitor
and the 150K-ohm
resistor
in the coil
assembly form
the
grid-leak
bias
network
for
the tube.
c.
The
bfo utilizes
the filament
and first
trvo
grids
of a
1R5
pentagrid
tube. Filament
volt-
iijr-e is
obtained from the 1.4-volt
d-c
potential
i'
pin
11 of
J4
through
r-f filter
choke L2.
rpacitor
C45 bypasses to
ground
the
audio
rìquency
at the filament.
Oscillator
plate
volt-
r,q€ is
supplied from
the 90-volt d-c
potential
48
at
pin
6
of
J4 through
a
portion
of
T13
and
voltage-droppinC
r.esistors
R28
and
R29
con-
nected
in
parallel,
l-hen
switch
52 is
in
C.W.,
NET,
or
CAL.
position.
Capacitor
C4l keeps
the center
tap
of the
bfo
tank
coil
at
r-f
ground
potential.
d.
The
third
harmonic
of
the
bfo
signal
is
coupled
from
the
gricl (pin
4)
of VT
and
fed
through
resistor
R11
ancl
capacitor
C24
to
the
grid
of
seconcl
i-f
umplifier
tube
Vb.
The
bfo
signal
mixes
rvith
the i-f
signal
to
produce
an
audible
difference
ft'eqnency,
rvhich
is
detected
and
amplified
in
the usnal
manner.
e.
Section 1,
rear,
of PHN.-C.W.-NTET-CAL.
sx'itch
52 disables
the
bfo r.vhen
the srvitch
is in
PHNI.
position,
by connecting
the bfo
plate
circuit
to r-f
ground
through
capacitor.
C46.
63.
Colibrotion
Oscillotor,
Port
of
V5
(fig.
31)
n,.
A
portion
of
\r5 is connected
as
a crystal
oscillator rvhen
PHN.-C.\V.-NET-CAL.
su'itch
52 is in
the
CAL.
position,
and
the output
of
the oscillator
is
used
to calibrate
the
receiver
dial. The
harmonics
of the 200-kc
funclamental
frequency
are converted
to
the intermediate
i-f
frequency,
u'hich
is useci
to beat
against
the
bfo and
provide
an
auclio beat
for caliblation
purposes.
The filament
and first
two
grids
of
V5
(pentagrid
1R5)
are
nsed in
the oscillator
circuit.
ó.
The
oscillator is
a self-sustaining
modified
Pierce
oscillator,
the
fundamental
frequency
of
rvhich
is
crystal
controlled. The
output
at the
calibration
oscillator
plate (pin
3)
of
V5 is
coupled
to section 2,
front,
of BAND
SW. srvitch
51 by means
of a long u'ire
used
as a radiating
element
when the
oscillator is functioning,
and
used
as a disabling
element,
connected
to
ground,
in the PHN.,
C.W., and NET
positions
of
PHN.-C.W.-NET-CAL.
switch
S2.
The
tuned
circuit for
the oscillator
consists
of
Crystal
Unit CR-2
/U
and
the
paralleled
coil
and 345-
ypf capacitor
connected rvithin
coil
assembly
TL2.
c.
Grid-leak bias is developed
when
the crys-
tal
is
excited. Resistor
R14 and
capacitor
C25
form
the
grid-leak
bias network.
Filament
volt-
age
is
obtained from
the l.4-volt
d-c
potential
at
pin
11 of
J4.
Plate
voltage is
supplied from
the
90-volt d-c
potential
at
pin
6
of J4 through
the
l0K-ohm
resistor in
Tl2 coil
assembly,
the
AGO 313A