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I MODEL 4OO TRANSCEIVER
C.
Ope ration (C ont)
n o t b e p o s s i b l e t o f i n d a r r d i p | w i t h
the PA PLATE
control.
r.or this
r e a s o n , b e s u r e t o o b 6 e r v e t h e f i r s t
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
d i p s t o l e s B t h a n 5 0 0 m a , ,
i n c l e a s e
loading
by rotating
the PA I.OAD
c o n t r o l s c l o c k w i s e ,
A f t e r e a c h i n -
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
4 5 0 - 5 0 0 m a .
T h e n s w i t c h b a c k t o
R E C E I V E .
CAUTION:
Do lrot hold the tlans-
c e i v e r i n T U N E p o s i t i o n J o r m o r e
t h a n 3 0 s e c o n d s a t a t i m e ,
e v e n
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
d o d u r i n B n o r m a l v o i c e t r a n s r n i s -
sion,
60 a short tuning period lnu6t
b e o b s e r v e d -
A--,4.,.1t*La''.a?,:!a,a;aa'.-J.aI.A
aLLI.L.. /^ l. .-..2 o '.I
-4,
6 .
U n d e r s o m e c o n d i t i o n s , i t m a y n o r
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
m a . o n e i t h e r s i d e o f r e s o n a n c e , i t
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
w a t t s w h e n y o u l o a d l o 4 0 0 m a . i n
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
4 0 0 m a . , o r s o , i t i s p l o b a b l y t i m e
to leplace the 6HF5 tubes, and
possibly tbe 6GK6 driver.
The other
tubes should also be checked at that
t i m e .
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.
8 0
4 0
2 0
I O
P O S . 7
8
9
9
l 0
A large deviation from theBe po6ition8
indicates a possible matching problem,
althouSh operation may 6till be quite
B a t i s f a c t o r y . P A L O A D s w i t c h p o s i -
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-
t o - T a l k b u t t o n o n t h e m i k e a n d c a r e -
fully set the CAR, BAL. control for
minirnum meter readin8,
While
speaking into the mike, slowly rotate
7 .
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