DRAKE TR-4CW - Page 28

product detector tube V16, through the SIDE-
TONE control, to provide audio output from the
speaker for CW monitoring. Audio output from V2
is
also
applied
to
the
grid
of
the
VOX
amplifier
tube, VI19A, which causes relays K1 and K2 to
close. The relays turn on the transmitter, cause
the 9.0 MHz oscillator to be shifted to 9.001 MHz
and apply a variable source of DC, controlled by
half of the XMTR GAIN control, to the balanced
modulator. The DC voltage which unbalances the
modulator increases the carrier to a suitable level.
The resulting 9.001 MHz signal from the balanced
modulator is amplified by V15 and coupled into
the crystal filter. The SIDEBAND control must be
in the ‘‘X” position to allow the signal to pass. A
screen resistor is switched into the final amplifier
screen circuit to prevent excessive screen current in
the X-CW position of the Mode switch.
When the Mode switch is placed in the X-AM posi-
tion the AM screen modulator V14 is inserted in
series with the final amplifier screen supply and a
constant voltage is applied to the balanced modula-
DRAKE
tor.
Relay
K2
shifts
the
9
MHz
oscillator
to
9.001
on
transmit
just
as
it
does
on
X-CW.
Vox
and
PTT
functions
are
the
same
on
AM
as
on
SSB.
When
relay
K1
is
closed,
either
by
the
VOX
circuit
or
the
push-to-talk
switch,
the
cathode
of
V3B,
V7,
V11
and
V12
are
isolated
from
ground
which
dis-
ables
the
receiver.
The
cathodes
of
V4,
V6,
V8,
V9,
V10
and
V15
are
connected
to
ground
which
actu-
ates
the
transmitter.
Also,
the
antenna
is
switched
from
the
receiver
input
to
the
final
amplifier
tank
circuit.
If
the
TCVR/RCVR
switch
is
in
the
RCVR
position,
the
RCVR
MUTE
jack
is
grounded
through
RFC
11!
and
RFC
7
and
the
antenna
is
connected
to
the
RCVR
ANT
jack
instead
of
T9
in
the
receive
condition
of
the
relays.
Pushing
in
the
LOAD
control
disconnects
the
plate
current
meter
from
the
final
amplifier
cathode
cir-
cuit
and
connects
it
to
the
diode
D9
and
its
associa-
ted
circuitry.
This
network
samples
the
RF
output
voltage
at
the
antenna
connection,
rectifies
it,
and
applies
it
across
the
meter.