Eico HF-20 - Page 21

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
W
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%.