I MODEL 4OO TRANSCEIVER
C.
Ope ration
(C
ont)
not be possible to find
arrdip| with
the
PA
PLATE control. r.or this
reason,
be sure to ob6erve the first
sentence
in this section,
Step
4.
5,
Rotate the REC. TUNE
switch
to
TUNE position.
Ouickly
check
the
PA PLATE control for
|dip|
o!
minimom leading. If the meter
dips
to
lesB than 500 ma,, inclease
loading by rotating the PA I.OAD
controls
clockwise, After each
in-
crease in PA LOAD,
resonate
the
PA PLATE again; that is, adjust it
for dip. Continue increasing PA
LOAD until the PA PLATE dips to
450-500 ma. Then switch back to
RECEIVE.
CAUTION: Do lrot hold the tlans-
ceiver in TUNE
position
Jor more
than 30 seconds at a time, even
though
PA PLATE is re€onated,
With fuu
grid
drive
to
the
6H!'5 PA
tubes, which
you
have in TUNE
position, they
are
dis6ipating
con8iderably more
powe!
than they
do durinB
normal voice transrnis-
sion, 60 a short
tuning
period
lnu6t
be observed-
A--,4.,.1t*La''.a?,:!a,a;aa'.-J.aI.A
aLLI.L..
/^
l.
.-..2
o
'.I
-4,
6. Under some conditions, it may
nor
be possible to load up to 500 ma,
This fnay occur with lowe! than
norhal line
voltage
or tubes not
quite up to par, particularly on l0
rneteis, The curlent increase when
tuning the
plate
circuit ofl resonance
will
provide
a
clue
as
to how {ar the
power ampli{ier can be loaded.
Il
the meter s\rings up to 600 or ?00
ma. on either side of resonance, it
will be easy to load up to 500 or even
more,
But, if the tubes
dra\r
ju6t
500 ma.
off resonance,
you
can only
load
to 400 or 450 rna. This is
not
necessarily a sign
that
you
have
a
problem, Peak input
power
with
voice
modulation will still
be
400
watts
when you
load
lo
400
ma. in
TUNE
position. A new pair of PA
tubes may allow
yor.1 to Load higher,
o! possibly
a
new drivet tube will
help. Plirnalily, the level
to
which
you can load will serve as an indica-
tion
of
when
tubes are deteriorating.
If
you can load to 500 ma. when the
set
is new, and after a few monthg
of operating you cannot
get
above
400 ma., or so, it is
plobably
time
to leplace the 6HF5 tubes, and
possibly
tbe
6GK6
driver. The
other
tubes should also be checked at that
time.
AVERAGE PA LOAD SWITCH POSI-
TIONS. The
{oUowinS
po6itionB
are
{or a 50
ohrn non-inductive load,
and indicate approximately
lphere
the PA LOAD srritch will end if the
antenna and coaxial cable are well
matched.
BAND PA LOAD SWITCH
'7.
80
40
20
IO
POS. 7
8
9
9
l0
A large
deviation from theBe po6ition8
indicates a
possible
matching
problem,
althouSh
operation may 6till be
quite
Batisfactory.
PA LOAD switch
posi-
tions below 5 will
generauy
be
needed only with very low impedance
loadB, such as a 75 rneter rnobile
antenna with
center loading coil.
VOICE TRANSMISSION.
After tuning
up
as
outlined above,
piess
the Push-
to-Talk button on the mike and care-
fully set the CAR,
BAL. control for
minirnum
meter readin8, While
speaking into the
mike, slowly rotate
7.
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