Heathkit SB-10 - Page 54

(,/)
Return
the transmitter
and adapter
to
80M
and,
with
the
function
switch
in manual
position'
tune
up
once again.
Now
adjust
carrier
nultA
and
carrier
null
B simultaneously
for
a
min-
imummeterreading.Thetwocontrolswillinteractanditshouldbepossibletonullthe
carrier
to
a
point
where
there
is no
meter
leading.
once a
null
is obtained,
both carrier
null controls
should
be
approximately
in
mid-position'
(
,)
connect
a
hi-impedance
microphone
(crystalor
dynamic)
tothe
microphone
input
connector'
place
the transmitter
meier
s;itch
in
th;
final
amplifier
grid
current
position._.Whi1e
speak-
ing into
the
microphone,
advance
the
audio.
gain
control
lrom
its
full ccw
position. At
"pi""*it"t"f'
ZS%
"otaUJn
otthe
gain
control,
the SB-10
meter
should
hit
a maximum
read-
inj on
voice
peaks
that
is
about
oni-thirdthe
maximum
reading
before
the carrier
was sup-
pressed. At the
same
time,
the
transmitter
mete-r should
begin
to show
slight
vertical
up-
wardkicksinfinatgridcurrentintheorderofafractionofamilliampere.Donotadvance
the audio
gain
control
beyond
this
point.
(..
)
place
the
function
"*ii"n
i"
the
VOX
positio'
without
changing
any other
setting.
While
'speakingintot}remicrophone,advancethe.transmittersensitivitycontrolontherearapron
'
of
the
SB-10
from
it" tuiiCCw
position
until
your
normal operating
voice
produces
positive
r
relay
operation.
rne
setting
of
this
control
will
vary
slightly
for
different
microphones
and
voices,
The relay
strggra
ffiupon
anyhesitation
in speech,
indicating
proper
vox
operatio4.r
(r
)
Return
the function
Switch
to
STANDBY
position
and,
noting
its
present
position
for
future
reference,
turn the
audio
gain
full
ccw.
Place the lunction
switch
in MANUAL
position
alrd
re
-
insert
some a.r"iu.'uy
?oirting
one
carriernull
control
(eitheiAor
B) until about
one-half
of the maximum
unsuppiessed
carrier
SB-10
meter
reading
is obtained'
(
,)
Make
sure a
dummy load
(incandescent
lamp
of suitable
wattage)
is
connected
to
the
RF out-
put
of the transmitter.
Place
the
transmitter
meter
switch
i.n
the
f
inal
plate
current
position
and the loading
control
at
its minimum
position.
Place the transmitter
plate
switch in the
ON
position
aid tune
the
final
amplifier
for
minimurn
plate
current.
Insert
maximum
car-
riei byfurther
rotating the
carrier
null
control
previouslyused
for
partial
carrier
insertion
to
its Lxtreme
positio;
Now
Ioad
the
final
amplifier
to
250 ma
usingnormal
loading
proce-
dure.
Load the
final
quickly
to avoid
damage
tothe tubes
due
to excessiveplate
dissipation.
(
)
Leave the
transmitter
plate
switch
in theON
position
and
null the carrier
once
again
by
re-
turning
the
carrier
null
control
used
for
carrier
Ie-insertion
to
the
minimum
sB-10
meter
readin*gposition.Thedummyloadlampshouldbedarkwiththecarrielsuppressedandthe
tinat amptfler
plate
current
should
be
at
its 50
ma
restins value'
(
,)
place
the function
switch
in
VOX
position
without changing
any other
control
settings.
Ad-
varce
the audio
gain
control
to the
point
previously noted and
speak
into the
ndcrophone.
The
dummy
load lamp
brilliance,
final
amplifier
plate
current,
and sB-10
mete1.
reading
will
peak
together
on voice
peals.
Check
the final
amplifier
grid
current;
the
meter
should
kick
up
veiy
slightly
ott
"*t"e^"
voice
peaks.
On voice,
the meter
reading
final
ampli-
fier
piate
crr"""tit
cinnot
respond
fast
enough to read
actual
current
peahs. Therefore,
while
the final amplifier
is
loaded
to 250 ma,
the
peak
reading
under modulation
should
be
only
100
to 125 ma
to
prevent
"flat-topping".
(
)
Witit
the function
swiich
in
vox
position,
check
to see if
the final
amplifier
plate
current
and driver
plate
current
go
to
zero
when
standing
by and
the relay
opens'
This indicates
proper
connections
in
the VOX
relay
circuit'
(
)
furn
the transmitter
plate
switch
bFF
and
return
the SB-10
function
switch
to
STANDBY
and the
audio
gain
fuU
CCW'
NOTE: An audio
generator capable
oI
producing
a clean
1000 cps
sine
wave will
be required
to
perform
the following
steps,
An oscilloscope
is
also
desirable
but will
not be
necessary
if a
good
selectable
sidebind
S-SB
receiver
is
available.
If these
items are
not
part
of
the builders
ham shack test
equipment,
they
can
usually
be
borrowed
from another
ham
or a radio-Tv
ser-
vice
shop. For the
amateur
contemplating
extensive
ssB operation,
the
purchase of these
two
items will
prove
a wise
investment,
These
items
will also
find numerous
other
uses
around the
ham
shack, A complete
line
of suitable
test
equipment
isofferedinkit
formbythe
Heath
Company.
Page 54