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The modulator valve is another tj6G having its two triode
.sections
connected in push'•pull, and which operates cJ,.,s
"B".
It is transformer•.
coupled
to the output of
a
type I F)G driver valve whose grid is in tum
connected to the microphone tr1nsformer. Bias for both these audio valves
is
obtained fcom the
4,
volt cap on the
"C'
battery, which
is
mounted on
the
chasm base
bthind the
relay.
Microphone current is obt•ined from the
Hansmitter filament
circuit
and
is
applied to the
microphone
through the
primary of the microphone transformer.
Keying of the
c.rrier
for c-w operation is accomplished by opening the
grid
circuit
of the p-a valve.
This
takes place when the key cable is pushed
into the jack designated KEY on the front panel. The break is transferred
to the
key
contacts,
and so is
closed
when the key
is
pressed. This method of
keying is not perfect, since a small amount
of
power will f_eed through
due
10 impcrfC<"t
ncutraliution.
HowC\'Cr. a difference in signal
level.
between
key
up and key down
of
approximately 2' db will be obtained
·with
an
average adjustment.
It
._,,JI
be noted
that when the
key
plug is pushed in,
back
contacts·
on the jack
operate
to open the fibmfflt circuit to the ·modu•
la.toe valves
to conserve
b.ittcry
current. and
also
insert
a rC$istaoce in
series
with
the
filaments
of
the r-f vdves to m•int,in approximately constant
filament
voltage
on
these latter v,Jves
in
spite of the
,educed
volrase drop in
the filament rheostat.
.
The meter mounted on the Cront pa.nel is arranged to measure the
transmitter
plate
and
filament supnlv
voftages as
well
,s
the
plate current
to
the
p·• stage. This is accomplished by using a
low
current meter in
conjunction
with volage multipliers and a current shunt, these being
switched by the meter switch 54 which is located below the
meter
.
.
The
inain sale of the meter is
alibra.ttd 0-,0
ma for p-a plate current measure-
ments. this sale being read when the
meter
,.,.·itch is in the position marked
TRANS
TIJNE.
When the switch is moved to B VOL TS, the full scale
range is 200 volts, although
a
complete
calibration docs not appear on the
meter
scale,
but merely spot calibr1tions at.180, 144 and 120
volts.
The
0-)
scale obtainable with the switch in
the
TRA"!S FIL l'°'ition is only marked
2.1) volts at • red line on the m1in
s«le,
is this ,s the only reading
·
of
interest on this range.
..
'
··
~
The
main tuning
dials of both
the t<1nsmitte, and the
receiver sections
mre fitted with
clamps that
act on the periphery of
the dial
scales, and
so 'lock
the
condensers
in any
desired
position.
These
locks locate at
the
extreme ends
of the
front
~nel.
PRELTMINARY ADJUSTMENT
On receipt of the equipment
it
should
be carefully examined
for
possible
damage
in
mnsit.
Before
lea,ing.the Faclory,
each set is
thoroughly insyected
and
tested, using the
customers C')'$tals
if these arc
available.
Othcrw,sc the
transmitter section
is tested using st:mdard
test crystals
at
either
end of
its
frequency
range, and ,ince the
,djustments are not
numerous,
no difficulty
should be
<Xf"'rienccd
in
tuning
it to
the desired
freq uency in the /idd.
7
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