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7.
If
no
or
low
B+ voltage
on
tube,
cheek
decoupling
path
for
open
or defective
R13.R21 ,R22,R31,R43,
and
filter
capa-
citor
C26B,
C27A-B-C-D
for ihort.
8.
If
wiring
and
circuit
component*
including the tube
check
O.
K.
and
Bt voltage
I*
excessive,
check
the
decoupling
path
for short
or defective
R13, R21
,
R22, R31, R43.
Suspected
trouble
In
the equalization, tone, loudness,
and
level controls
and
networks should
lead
to
specific resistance
and
capacitance checks
to
localize the trouble.
In
general.
If
the user suspects poor
frequency
response, defective
equal-
ization, or
defective operation of the tone or loudness
controls,
the amplifier should
be
tested
thoroughly with
audio gen-
erator,
vtvm, aqd
scope.
VOLTAGE
CHART
TUBE
VI
12AX7
V2
12AX7
V3
12AU7A
V4
12AU7A
VS
6L6GB
V6
6L6GB
V7
5U4GB
PIN*
1
72
84
60
135
*
»
0
0
-
2
0
0
0
0
35
35
410
HR
3
0.65
0.75
1.4
4.8
400
400
-
4
H
H
H
H
405
405
370VAC
5
H
H
H
H
0
0
-
6
37
75
210
140
.
«
-
370V
AC
7
-0.2
0
60
0
H
H
8
0.35
0.85
65
4.8
H
H
410
HR
9
H
H
H
H
-
-
REFERENCES
FOR
VOLTAGE 4
RESISTANCE
CHARTS
H
"
Heater
pin;
all
biased
35
volts
de above
chassis
ground
to
prevent heater-cathode
current.
Heater
AC
voltages as
follows:
a)
VI, V2,V3,
V4
:
6.3VAC
from
pin
9
to pins
4
&
5; b)
V5,
V6:
6.
3
VAC
between
pins
2
&
8.
HR"
Heater
pin of
Rectifier
V7
:
5VAC
between
pins
2
4,8;
check only
with
V7
socket
empty.
—
Not
connection
to
tube
element
or
not contact
on
socket.
UNLESS OTHERWISE INDICATED, ALL
VOLTAGES
ARE
DC,
POSITIVE
AND
MEASURED
TO
CHASSIS.
Line Voltage:
115volts,
60cps
All
measurements are
made
with
VTVM
of
approximately
1
1
meg
Input
Impedance.
AC
mid-frequency
(1
kc) voltage
sensitivities for
20
output
are'shownon
the schematic
diagram.
Set
LEVEL
4
LOUDNESS
controls
at
max. (lO)andBASS TREBLE con-
trols
at
flat (0) for
these checks.
CONTROL
SETTINGS FOR
SELECTOR
"
RIAA
LEVEL
4 LOUDNESS
-
Min.
(0)
BASS
4
TREBLE
-
Flat
(0)
TRANSFORMER DC
WINDING
RESISTANCES (COLD)
T1
primary (black
leads)
"2.
30
T1
secondary
(red leads)
"1660
T2
plate-to-plate (blue
to
brown)
"3150
T2
screen- to-screen (blue-yel.
to
brown-yel.)
"1350
72
common
(black)
to
40
tap (white)
"0.50
T2
common
(black)
to
80
tap (green)
"0.80
T2
common
(black)
to
160
tap (yellow)
"1.10
ALL
VOLTAGE
AND
RESISTANCE
VALUES
MAY
NOR-
MALLY VARY
BY
± 15%.
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