40
.22
SERVICE MANUAL
b.
Page 2
fier
Q5103.
Traosistors
Q5103
aod
Q5104
are
conoected
in a
Darlington
configuratioo
which is characterized
by
a
high ioput i6-
pedance
and a
low output
impedaace,
The
output of
Q5104
is
then
coupled
to the
AVC
circuit, the TREBLE, BASS
aod VOLUME
controls and the
predriver
stage.
AVC
Circuit
A saopling of
the
output
of
Q5104
is coupled
through C5105 to
the base
of
Q5105.
The
output from the collector of
Q5105
is recti-
fieci by diode CR5106 creating
a d.c. voltage.
This voltage varies with
the
average aopli-
tude
of
the
signal
voltage applied to
Q5105.
This
varyiog d.c. voltage
is
direcdy coupled
to the ceoter of dual diode CR5l05, If
a
large signal
voltage
is
coupled
to
Q5105,
then a large
d.c, signal
is coupled
to
diodes
CR5104 and CR5105.
This latge signal
forward biases the diodes
effectively
de-
creasing their resistance. As the
resistance
decreases,
oore
of
the signal voltage at the
base of
Q5103
is shunted to
gtouod
effec-
tively
decreasiog
the irput s.ignal
to
Q5101.
Treble, Bass. Volume
and
Gsin
Set Controls
The
TREBLE
and BASS cootrols are
io paral-
lel with the ouqrut froo
Q5104.
The TREBLE
control vaties the atount
of high
&equeocies
fed though the VOLUME
control to the pre-
driver stage,
Q5106.
The BASS coottol
varies
the
aoouat of low
frequencies fed to
Q5106.
The
VOLUME
contlol
varies the amouot of
drive to the base of
Q5106.
The
indiv.idual
Gain
Set
Controls
coopeosate fot
gaio
diffetences of
the voltage anplifier aod,/or
power
aoplifier.
It
is
also
used to balaocc
tle
systeo.
Predriver,
Driver
and Power
4mplifier
Stages
The ouput ftoo
tbe
VOLUME
cootrol is
capacitively coupled to the base of
predriver
stage
Q5106.
The
ouput of
Q5106
feeds
the
bases
of driver
stages
Q5107
aod
Q5108.
Power aoplifier stages
Qr109
and
Q5110
are
operated
in
a
coopliocotary syutoery coo-
figuratioo vhich
produces the
power
rcquired
to
drive the output
tansforoer, T5102.
Short C ircuit Protectlon
Circuit
This circuit
prcvcots aaplificr daEagc
duc
to
short
circuits,
ovcrloads or
iocorrcct con-
SOLID
STATE
STEREO AMPLIFIER,
Type T5A6
oectioos
io the speaker system, If
a
coodi-
tion occurs
in the speaker systeo
that oay
result
io daoage to the
aoplifier, the
short
circuit
protectioo circuit
biascs the inPut
transistors
ioto cut-off.
Refer
to
Schematic Diagrao.
The output
cutreot
is
mooitored by oeasuriog the
voltage
actoss eoitter
resistor R5128. As
the curedt
thtough Rll28
iocteases, capacitor Crl22
charges
in the
polarity
shown. For
any
particular
tioe
period
the
potential reached
is
only a fraction of the
Poteotial
at the
emitter resistor due to
the tine coostaot
determined
by
DELAY TIME
poteatioaeter
R5143A
aod the
voltage
dividet
coosisting
of
R5136
aod R5ll7.
If
rhe curtent
through
R5128
iocreases
eoough,
capacitot C5122
will charge
to
a
potential that results
in the
conduction
of
Q5111.
When
Q5111
cooducts
its
collector cuffent
foiward biases
Q5112
causing
Q5112
to cooduct.
Due
to feedback
betweeo
the traosistors, both
Q5lll
aod
Qtll2
saturate aad becooe
iodependent of
c5122.
Vheo
Q5112
saturates,
the
potention
oo
the
collector
rises froo
-20
volts to Dear zero.
This change
in poteotial is coupled though
R5110
to dre forward bias
CR5102,
thereby
reducing
the collector voltage of
Q5101
in
the Pre-Aoplifier
to practically zero.
This
cuts
off
the first
stage of
the
Pre-Aoplifier
prcvetrtiog aoy funher sigoel froo
passing
though the aoplifier.
Since
the
power
aoplifier stages are operatiog
aear class B,
no input results in very little cnrreot
flow.
Mute Relay
The
oute telay
(K5101)
is used to quiet the
aoplifiet
before
record
uansfer
takes place
to avoid uopleasaot
noise
in tbe output.
The
relay is eoergized whenever
the
trip switch
io the
Select-O-Madc
Mechaoiso
is closed,
A
holding circuit for the outc relay is coo-
pleted
through
cootacts
3Ml1
ol the cao
switch
is the oecheniso. Thcsc cootacts
ate
closcd whea the
aechaniso is ia tbe trans-
fer
or
scan
positioo,
d.
e,
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