Heathkit DX-40 User Manual

So
that
the
amateur
may
be
guided
in
his
purchases
of
crystals
for
this
transmitter
it
may
be
best
to
mention
that
only
160,
80,
or
40
meter
crystals
be
used,
with
the
preference
being
80
and
40
meter,
the
fact
being
that
some
additional
feedback
maybe
required
inthe
oscillator
cir-
cuit
for
certain
160
meter
crystals.
Sufficient
grid
drive
to
the
6146
final
should
be
obtained
froman
80-meter
crystal
for
operation
on
80
through
10
meters,
while
only
slightly
more
efficiency
is
evident
on
the
higher
frequency
bands
by
using
a
40-meter
crystal.
The
tuning
range
of
this
transmitter
is
limited
to
the
80,
40,
20,
15,
10
and
11
meter
bands.
Operation
on
the
160-meter
band
should
not
be
attempted.
BUFFER:
The
buffer
stage
is
coupled
to
the
6146
final
amplifier
by
a
Pi
network
circuit
which
has
a
tuning
range
limited
to
the
amateur
bands.
This
limitation
avoids
tuning
a
wrong
harmonic
which
would
be
amplified
by
the
6146
stage.
This
method
of
coupling
helps
materially
in
sta-
bilizing
the
final
amplifier,
at
the
same
time
attenuating
the
higher
order
harmonics.
This
buffer
stage
has
an
independent
filament
supply
to
prevent
heater-to-cathode
breakdown
as
this
cathode
is
300
volts
potential
above
the
other
tubes.
FINAL
AMPLIFIER:
The
plate
circuit
ofthe
final
amplifier
is
shunt
fed
with
a
.425
mh
RF
choke
and
is
capacity
coupled
into
the
Pi
network
tank
circuit.
For
operation
on
80
meters
a
68
wyt
4
kv
fixed
capacitor
is
automatically
paralleled
with
the
plate
tuning
capacitor
by
means
of
the
bandswitch.
A
900
ppf
variable
capacitor
is
permanently
connected
across
the
output
of
the
Pi
circuit
for
antenna
loading.
MODULATOR:
A
12AX7
tube
is
used
as
a
high
gaintwo
stage
resistance
coupled
speech
ampli-
fier.
The
constants
of
the
entire
speech
amplifier
and
driver
stages
have
been
carefully
chosen
for
maximum
gain
at
voice
frequencies.
This
allows
a
higher
average
level
of
modulation
to
be
maintained
where
it
will
be
the
most
effective.
Also,
a
simple
radio
frequency
filter
network
has
been
incorporated
inthe
microphone
input
circuit
to
discourage
RF
from
getting
in
the
audio
circuit
and
causing
an
annoying
feedback.
The
audio
energy
from
the
speech
amplifier
is
coupled
to
the
gridof
one
triode
section
of
a
6DE7.
This
tube
contains
two
dissimilar
triode
sections.
One
triode
section
is
rated
at
1.5
watts
dissi-
pation
and
the
other
at
7
watts
dissipation.
The
lower
rated
triode
is
used
as
a
direct
coupled
driver,
its
plate
being
tied
to
the
contro}
grid
of
the
heavier
duty
triode
which
forms
the
modu-
lator.
This
second
triode
is
biased
sufficiently
to
limit
its
conduction
and
therefore
the
screen
voltage
on
the
final,
which
results
in
a
low
resting
carrier.
With
modulation
the
conduction
of
the
heavy
duty
triode
section
is
varied
in
accordance
with
the
average
voice
level.
This
gives
a
controlled
carrier
effect
by
varying
the
screen
voltage
on
the
6146
tube,
at
the
same
time
the
audio
signal
is
superimposed
on
this
variable
voltage.
The
net
result
is
to
producea
carrier
output
which
increases
with
the
percentage
of
modulation
applied.
POWER
SUPPLY:
The
power
supply
consists
of
a
transformer-operated
full
wave
rectifier
cir-
cuit
with
a
choke
input
filter.
Two
filter
capacitors
are
operated
in
series
to
withstand
the
voltage
involved.
Two
identical
resistors
across
the
filter
capacitors
serve
a
dual
purpose
of
equalizing
the
filter
voltage
and
acting
as
a
bleeder
resistor
to
stabilize
the
output
under
varying
load
conditions.
A
5U4GB
tube
is
used
as
the
full
wave
rectifier.
This
tube
is
a
heavy-duty
version
of
the
regular
5U4G.
Some
of
the
tube
ratings
have
been
exceeded
while
others
are
operated
under
the
maximum
permissible.
Tests
have
indicated
that
by
using
the
heavy
duty
tube
with
choke
input
and
a
light
current
load,
no
difficulty
should
be
encountered.
NOTES
ON
ASSEMBLY
AND
WIRING
Many
of
these
kits
will
probably
be
constructed
by
people
just
starting
in
the
amateur
radio
field.
Consequently,
the
step-by-step
instructions
in
this
manual
have
been
covered
in
considerable
detail.
Read
each
step
completely
through
and
be
sure
it
is
understood
before
proceeding
with
the
operation
called
for.
This
will
assure
that
a
complicated
step
is
performed
in
the
proper
sequence
in
order
to
complete
it
with
the
least
possible
difficulty.
Page 4

Heathkit DX-40 Specifications

General

Brand	Heathkit
Model	DX-40
Category	Transmitter
Language	English