Heathkit DX-40 - ANALYZING AND ISOLATION; Power Supply Troubleshooting; Oscillator and Buffer Stage Checks

ANALYZING AND ISOLATION
The
transmitter
can
be
divided
into
stages.
Each
stage
can
then
be
isolated
and
worked
on
in-
dividually.
In
the
next
section,
simple
steps
willbe
outlined
to
test
each
stage.
A
Vacuum
Tube
Voltmeter
or
Multimeter
is
necessary
to
check
voltages
and
resistance.
Voltages
listed
were
made
witha
Heathkit
Multi-purpose
VTVM
(Vacuum
Tube
Voltmeter).
The
line
voltage
was
115
volts
AC.
The
transmitter
was
set
up
for
crystal
controlled
80-meter
PHONE
operation
(key
circuit
closed)
for
most
checks.
Voltages
listed
do
not
necessarily
indicate
those
in
your
transmitter.
Line
voltage
variation,
component
tolerance
and
the
presence
of
RF
will
cause
variations.
They
should
only
serve
as
a
basis
of
comparison.
AC
filament
voltage
may
read
high
due
to
the
presence
of
RF
which
affects
the
readings
on
vacuum
tube
type
voltmeters.
A
more
conclusive
check
inthis
case
may
be
obtained
with
a
meter
such
as
the
Heathkit
Volt-Ohm-Milliammeter.
POWER SUPPLY
TUBE
E
5U4GB
RECTIFIER
1.
Check
the
rectifier
tube
E
by
substitution.
Be
sure
the
socket
is
wired
to
the
correct
pin
connections.
+
2. REMOVE THE LINE CORD FROM THE POWER SOURCE. Make certain that the filter capa-
citors
are
discharged.
Test
the
filter
capacitors
and
high
voltage
circuit
by
measuring
the
resistance
between
pin
#1
of
the
5U4GB
rectifier
tube
E
and
the
chassis.
It
should
read
be-
tween
40
KQ
and
50
KQ
in
all
positions
of
the
operation
switch.
A
much
lower
resistance
reading
may
indicate
a
short
circuit
in
the
B+
circuit,
a
leaky
or
shorted
filter
capacitor,
or
the
ohmmeter
leads
not
polarized
properly.
The
meter
polarity
should
favor
the
higher
t .
3.
Sees
Ta
operation
switch
for
open
contacts,
or
solder
that
has
run
into
the
contacts.
4.
Test
the
transformer
by
removing
the
rectifier
tube
E
and
measuring
the
AC
voltages.
The
voltage
between
the
yellow
leads
should
read
approximately
5
volts.
The
voltage
between
each
red
lead
and
the
center
tap
should
be
700
to
800
volts.
The
center
tap
is
the
yellow
and
red
lead.
Both
filament
windings
should
read
approximately
6.3
volts
AC.
The
green
_
leads
are
filament
winding
#1
and
the
white
leads
are
filament
winding
#2.
5.
Inspect
the
filter
capacitors
and
see
that
they
are
polarized
properly.
If
not,
they
should
be
replaced
if
current
has
been
allowed
to
flow
through
them
for
any
length
of
time.
OSCILLATOR STAGE
TUBE D 6CL6 OSCILLATOR:
Test the 6CL6 tube D by substitution.
Check
the
crystal
switch.
Make
sure
the
switch
is
turned
to
the
proper
crystal
or
VFO
position.
3.
Test
the
crystal
you
are
using
by
substituting
other
crystals
of
proper
frequency.
4.
Test
the
1.1
mh
RF
choke
in
the
cathode
circuit
for
an
"open"
winding
(POWER
OFF).
5.
Check
the
40-meter
plate
coil
for
an
"open"
winding
(POWER
OFF).
6.
a
bale
Filament
voltage
should
check
near
6.3
V
AC
from
pin
#4
on
socket
D
to
chassis.
Plate
voltage
should
read
approximately
225
to
275
volts,
depending
on
the
adjustment
of
the
drive
control.
This
reading
is
taken
from
#1
on
terminal
strip
FF
to
chassis,
in
the
TUNE
position.
8.
Screen
voltage
should
read
approximately
135
to
165
volts
depending
on
the
adjustment
of
the
drive
control.
This
reading
is
taken
from
Pin
#8
on
the
6CL6
socket
D
to
the
chassis.
BUFFER STAGE
TUBE C 6CL6 BUFFER:
1.
Test
the
6CL6
tube
C
by
substitution.
2.
DISCONNECT
THE
LINE
CORD.
Inspect
the
rotary
switch
contacts:
Be
sure
there
is
no
solder
on
the
contacts
and
that
each
is
making
a
good
electrical
connection
with
the
rotor.
Page 37