Heathkit DX-40 - Loading and Final Tuning

Upon obtaining a reading at, or near 3 milliamperes grid current to the final amplifier, switch
the meter to read plate current. The operation switch is switched to PHONE position and the
final tuning control is tuned to the lowest reading of plate current. This "dip" should occur near
#90 on the dial with the bandswitch on 10 meters.
NOTE:
These
tests
were
made
with
a
3500
kc
and
7000
ke
crystal.
The
"off-tuned"
plate
cur-
rent
generally
does
not
exceed
75
milliamperes
due
to
the
low
screen
voltage
on
the
6146
in
the
PHONE
position
without
modulation.
Once
tuned
to
minimum
current
in
the
PHONE
position,
switch
to
CW
operation.
This
wilt
show
a
much
higher
average
plate
current,
with
more
pro-
nounced
"dips".
.
To
load
the
antenna
or
dummy
load,
always
start
with
the
antenna
tuning
(loading)
control
closed
at
"O"
position.
The
final
tuning
is
always
tuned
to
resonance,
or
minimum
plate
current.
When.
the
loading
control
is
moved,
it
detunes
the
output
circuit
and
this
has
to
be
compensated
for
by
redipping
the
final
tuning
control
to
resonance.
Keeping
this
in
mind,
gradually
open
the
antenna
tuning
to
indicate
#20
on
the
dial.
Now
return
tothe
final
tuning
control
and
redip
it
to
minimum
current.
Increase
the
loading
to
approximately
40
on
the
dial.
Redip
the
final
to
minimum.
In-
crease
the
loading
still
farther
and
redip
the
final
until
the
"dip"
is
at,
or
near,
the
recommend-
ed
"loaded"
current
which
is
125
milliamperes
in
the
CW
position.
This
successive
loading
and
redipping
is
recommended
for
tuning
of.
the
pi
network
output
cir-
cuit
of
this
transmitter
except
when
using
an
antenna
tuner
or
coupler,
in
which
case
the
loading
capacitor
is
left
closed
at
or
near
the
'O"
position
to
provide
a
low
impedance.
It
would
be
more
convenient
to
make
the
operation
of
"loading"
two
handed.
Bringing
up
the
loading
with
the
left
hand
and
dipping
the
final
with
the
right
hand
in
succession
until
the
required
plate
current
is
reached.
With
a
little
practice
"loading"
willbe
no
problem.
When
loaded
to
the
full
CW
rating,
switch
to
PHONE
position
and
modulate.
With
sufficient
modulation
the
plate
current
should
kick-up
near
125
milliamperes
on
peaks.
If
alight
bulb
is
being
used
as
adummy
load
it
should
increase
in
brilliance
in
accordance
with
the
voice
level.
A
field
strength
meter
or
the
"S"
meter
on
the
station
receiver
will
also
show
a
definite
increase
in
carrier
level.
NOTE:
This
particular
modulation
system
requires
quite
heavy
antenna
loading.
Loading
to
the
CW
rating
and
then
switching
to
the
PHONE
position
is
customary
procedure.
It
has
been
noted
that
with
a
constant
audio
tone
of
sufficient
amplitude
the
RF
output
can
be
adjusted
to
maximum
with
greater
ease.
Depending
on
the
voice
of
the
operator,
the
gain
of
the
microphone,
and
the
amount
of
antenna
loading,
an
ideal
position
between
the
operator
and
the
microphone
should
be
chosen
and
maintained
for
proper
modulation.
Extremely
close
talking
with
a
high
gain
micro-
phone
should
be
avoided
to
prevent
clipping
of
modulation
peaks.
In
most
cases
the
RF
gain
control
of
the
receiver
has
to
be
reduced
and/or
the
antenna
removed
or
the
antenna
terminal
grounded
to
the
receiver
chassis
to
prevent
pinning
the
"S"
meter.
With
the
gain
reduced
on
the
receiver
to
prevent
overloading
the
AVC
or
causing
audio
feedback,
the
speech
should
sound
clear
and
distinct.
NOTE:
There
are
times
when
quite
heavy
loading
is
obtained
with
the
(antenna
tuning)
loading
capacitor
completely
closed
at
"O"
position.
This
will
occur
especially
at
the
low
frequency
end
of
the
80-meter
band
when
working
into
a
low
impedance
502
line.
When
this
occurs,
addi-
tional
capacity
will
be
required
in
parallel
with
the
2-gang
loading
capacitor.
See
Service
and
Maintenance
Hints.
INSTALLATION
AND
OPERATION
NOTE:
It
should
be
noted
that
an
Amateur
Radio
Operator
and
Station
License
is
required
to
place
this
transmitter
on
the
air.
Information
regarding
licensing
and
amateur
frequency
al-
locations
may
be
had
from
publications
of
the
Federal
Communications
Commission
or
the
Am-
erican
Radio
Relay
League.
This
transmitter
can
be
used
for
novice
operation
only
if
the
fol-
lowing
two
requirements
are
met:
(a)
CW
operation
only.
(b)
Crystal
control
only,
on
assigned
novice
frequencies.
Page 32