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T
ELECTRICAL CIRCUIT
Co
5.0V
5V4
-G
L,
-O
J
300V.
-300V.
10.5V.
-10.5
V.
6.3
V.
6.3V.
Fig. 6.
Circuit diagram of
the
SSB
Jr.
power supply
Circuit Constants
(All resistor,
and
capacitors
*20%
tolerance
unless
specified
otherwise)
C,
40
mf
450
volt electrolytic
Rx
..
1000
ohm
1
watt
C:, C,
50
mf
50
volt
electrolytic
S,
SPST toggle switch
J
Closed
circuit jack
or
terminal
posts
to
S.
DPDT
toggle switch
L
permit
metering
with
0-100
mil
meter
7
henry
choke,
160
mils
(UTC
R-20)
T
Power
transformer,
350-0-350
at
75
mils,
6.3
volts at
3
amperes,
5.0
volts at
3
R,
100
ohm
potentiometer
amperes
(UTC
R-11)
l
ferent ohmmeters may give different readings,
since
the diodes
are
non-linear in nature.)
It
is
recommended
that
transformers
T1, T2 and
T3
be as
specified.
Do not make any
substitution
un-
less
you wish to duplicate
a
long
series
of
tests to
determine
if
the substitutes
are
suitable. The types
indicated
are
standard parts, inexpensive, and
easy
to procure.
Observe
that
the connections
are
indicated
on
the
circuit
diagram by
their
color
code.
It
is
further
recommended
that
you
use
Millen
No.
69046
coil forms
as
specified.
While
the coils
are
not critical, they must
have
a
certain inductance
and
distributed
capacitance, and
if
you adhere to the
specifications given you should encounter absolutely
no
difficulty
coil
-wise.
The adjustment of the audio
phase
-shift network
circuits
is
most easily done
with
the
phase
-shift
sub-
assembly
out of the
chassis.
The resistors
R7
and
R.
(and
R10
and
Ro)
should bear the
ratio of
133,333
to
6
It
-.
Fig.
7.
SSB
Jr. Power
supply
100,000,
that
is,
4
to
3, as
closely
as
can
be
deter-
mined.
If
in doubt
as
to the
ratio of
the resistors
you
used,
double-check
their
value
on an
accurate
bridge. The
adjustment of
the
phase
-shift network
now consists
only of setting
the
four capacitors
(C7
through
C10)
to their proper values. Several methods
can
be
used.
The most accurate
will
be
described.
An audio oscillator
capable
of operation from
225
to
2750
cycles per second
(with
good
waveform)
is
required, plus
an
oscilloscope.
The oscillator should
be
carefully calibrated by
the method described
later. Connect the
output of
the audio oscillator
through
a
step-down
transformer (the Stancor A
-53C
will
serve
nicely) to
a
1000
ohm or
2000
ohm poten-
tiometer
with
the arm grounded.
Adjust
the arm
position
so
that
equal
(but
op-
posite) voltages appear
on each
half of
the poten-
tiometer. A steady audio frequency signal
of
any
convenient frequency may
be
used
with
an oscilloscope
acting
as
a
convenient
voltmeter for this job.
Swing
the
vertical
deflection lead from
one end
of
the
potentiometer to the other
and
adjust
the arm
to
obtain
equal voltages (a
true
center
tap).
Set
up
a
temporary
double cathode
-follower circuit
using
a
12AT7
with
500
ohms
from
each
cathode
to ground
and connect
as
shown in
Fig.
9.
(It
will
be
convenient
to
provide
leads
M,
N,
and
1
and
2
with
clips at the
ends
to facilitate checking.)
One
may
use
the 12AT7
in the
rig
as
the double cathode follower by temporar-
ily
short circuiting the plate of
each
tube to
its
respective center
tap of the
UTC
R -38A transformers.
Be sure
to remove the 12AU7 and the 6AG7 at this
time, and
of
course
supply operating voltages for the
12AT7. Pins
3
and
8
should connect to the
H
and
V
deflection amplifiers in the oscilloscope, and the oscil-
loscope common connection should
be
made
to the
chassis.
First
connect lead
M to terminal A
on the phase
-
shift unit,
and lead
N to terminal A'.
Connect
leads
1
and
2
to terminal M. (Note
that
the
dashed con-
nections
are
missing at
this
stage
of adjustment.)
I
4
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