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The output
of the
vox voltage ampli.fier
is
capacitively
coupled
to the
plate
of one section of a
6AL5 dual diode
and the output
of the anti-trip voltage
amplilier is
capacitively coupled to the
cathode
of the
second
6AL5 diode,
The
audio output
alternating current voltage which is developed
in
the anti-trip
voltage amplifier
is then rectified
and appears as a
negative
potential
at the
plate
of the other 6AL5 diode. The
diode
will not
conduct when so biased. Therefore,
the relay
control tlbe
(1/2
of a 12AT?)
remains
cut-off
by the fixed
bias applied to the cathode by
the voltage divider network.
From
this
"Anti-Trip"
action, it can be seen that
for the relay
to be tripped, it
wiII
be necessary
to upset
the negative
voltage at the
plate
of the diode,
thus allowing it
to conduct
and
place
suf-
ficient
positive
voltage on the
grid
ofthe
relay
control
tube to overcome
the fixed cutoff cathode
bias.
This
positive
"upsetting"
voltage
is developed
i.n
the speech
and vox amplifier stages and
originates
at
the microphone. Thus, with
proper
setting
of the sensitivity
controls, speaking
into
the microphone
trips the
relay
by overcomingthe
receiver
anti-trip
bias, but receiver
audio
entering
the microphone will not
trip the
relay
due
to
"in
phase
bias" developed
by the
anti-trip
circuit.
A
capacitor resistor
network
charges and
discharges
across
the
grid
of
the control tube to intro-
duce
the
necessary
time
delay
after
speech
is discontinued.
A
cathode
bias
voltage
divider
network onthe relay
control
fube is switched
in or outfor a selec-
tion of
voice control
or
manual
operation.
In
standby
position,
B+
is removed
from all circuits.
BALANC
ED
MODULATOR
CIRCUITRY
The input
circuit
to the
pair
of balanced modulators
consists of
a broadband RF Phase Shift
network
of the
passive
type. An entirely different
network
to
provide
the
proper phase
shift
at
each fundamental
input frequency is
switched
in on each
band. This design
feature
permits
operation
on all frequencies
in the
particular
band desired
without
the necessity of continual
adjustment,
but still
maintains a
very
high degree
of
precision
in
the RF
Phase
Shift
network.
The netnork
is
capacitively coupled to the balanced
modulator gridsi
The
cathodes of the bal-
anced
modulators
are
returned
to
ground
through
1000Q
tube balancing
or carrier
null
controls
which
are adjusted
from
the
front
panel.
The
plates
of the
tubes are tuned
to the
operating fre-
quency
with
a
multiband
coil
and capacitor circuit.
The
modulation
voltage developed in the
AF
modulator
is
coupled through
two 1:1
ratio
trans-
formers
to the
balanced modulator
grids.
A
sideband
selector switch
is
connected
in
the
output
Ieads
of the
transformers
which applies the audio
voltage in
the
proper phase
relationships to
obtain
upper,
lower,
or
double
sideband
(AM)
operation.
The RF
voltage
is isolated from
the
audio
network
by
the use of four 500 microhenry
chokes
to couple the audio to the
grids
of the
balanced
modulators.
DRIVER
AND
RF AMPLIFIER
CIRCUMRY
A6CL6tube
is
erqployed
asa Class
A driver stage.
The excellent
linear capabilities ofthe
6CL6
as
a Class A
amplifier
lends
itself
perfectly
to this
application. The
grid
of
the
6CL6 is coupled
through
acapacitor
to alink on the balanced modulator
output coil.
Bandswitch
selected,
broad-
band,
slug tuned
coils are used for tuning the driver
output circuit.
The output
circuitof the
driver stage is coupled
to the
grid
of
the
6BQ5
tube. This
stage is also
operating
in
Class
A serviceand is easily
driv-en
to maximum output while maintaining excellent
linearitv.
The
plate
circuit is shunt fed
and couples
to an all-band
Pi
network output circuit.
The
plate
circuit
also furnishes
a
sample
ofRF voltage
to operate the meter for the
purpose
of tuning the
adapter.
Page
8
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