Heathkit HW-12 - Carrier Oscillator

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while the charging of larger capacitor C88 gives
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asilow AVC release time, Resistors R80, Rizz,
R123, and R124, with capacitor C123, divide
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ihe AVC voltage applied to V9 and Vi2A and
provide decoupling, To pLovade delayed AVC,
resistor R123 is returned to the cathode of Vi2B
rather than to ground, This balances the AVC
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by Hoisé wnen no Sipiias is being
s
mall positive voltage toi EErOve
iti at low Sienal levels
sensitivity
at ale "a5 4
udio Signals from ViZA are fed to
the speaker socket through output transformer
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T4, To provide maximum intelligibility, the fre-
quency response of the Gurpus stage is limited
to the voice fre equency range by a sh iarp-cutoff,
fore)
high frequency, degenerative feedback loop, Gat
i 4197 +
frequencies across RFC120 causes its
pedance to rise. The high frequencies are scthug
returned out-of-phase to the grid of V12B.
This signal cancels out the incoming high fre-
quency audio and noise sionals at the erid of
See nates, EN RRR EAVES Sapam UD Ea OL
V12B. Capacitor C120 is a lowfrequency bypass
to ground. and capacitor C127 serves as 2
ho Br eenny
parasitic oscillation suppressor,
CARRIER OSCILLATOR
Carrier oscillator V11B supplies an RF signal to
the balanced modulator, and a heterodyning sig-
nal to product detector V11A. Tube V11B isa
Colpitts type oscillator. Crystal Y1 determines
the operating frequency to accurately maintain
the proper frequency relationship with the crystal
filter bandpass frequencies, Capacitors C117 and
C118 provide feedback to maintain oscillation,
The
output
is
taken
from
the
junction
of
ca-
pacitors C115 and C116,
VFO
Variable frequency oscillator V13 is also a
Colpitts type oscillator, which operates at low
frequencies
for
maximum
stability,
Coil
L5
pro-
vides the necessary inductance, while capacitors
C132, C133, and C134 form a divider for oscil-
lator feedback and output connections, C130 isa
negative
temperature
coefficient
capacitor
for
temperature
correction,
The
oscillator
output
is
taken
from
the
junction
of
capacitors
C133
and
Ci34,
and
is
applied
to
cathode
follower
vi14,
The
harmonics
are
suppressed
by
ca-
pacitor
Ci3$4,
The
signal
output
from
Vi4
is
connected
to
receiver
mixer
V8B
through
ca-
pacitor
Ci42,
and
to
transmitter
mixer
V4
through
a
filter
circuit
comprised
of
choke
RFC140,
and
capacitors
Ci40
and
Cidi.
The
filter
circuit
Separates
the
VFO
frequencies
from
the
IF
and
RF
signals
also
present
at
this
point,
thus
stopping
adie
leakthrough
ll
i A nave
which would cause
IF stages,
ACCESSORY CRYSTAL CALIBRATOR
The accessory plug-in crystal calibrator is
turned on by pulling out the knob of the AF
pesssls aes Va wast fan
Gain control, The calibrator filament circuit
is grounded internally to the calibrator chassis,
eial sre rnaity Mele CP ALIVI ALOL Cilla Ss
For this reason, the calibrator chassis must
not be grounded to the transceiver chassis,
Resistor. R6 is the calibrator plate current
return; resistor R5 drops the calibrator fila.
ment voltage to 6 volts. ~~
FILAMENTS
The
filament
wiring
of
the
Transceiver
is
aser-
ies-paraliel
arrangement
that
baiances
the
fila-
ment
voltage
without
wasting
power
in
dropping
resistors,
This
filament
arrangement
allows
the
use
of
both
6
volt
and
12
volt
filament
tubes
in
the
Transceiver
design,
The
filaments
of
RF
power
amplifiers
V6
and
V7
are
isolated
by
choke
RFC60
to
prevent
RF
energy
from
getting
to
the
other
tube
filaments,
POWER SUPPLY
Operating voltages for the Transceiver are pro-
vided
by
an
external
power
supply,
The
power
supply is turned on or off by aswitch on the rear
of
the
Transceiver
Function
switch,
This
off-on
switch is wired through the Transceiver power
plug to the external power supply,
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ie
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