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Grundig TK 20 - Technical Adjustments and Maintenance; Mains Voltage Adjustment Procedure; Diode Connection Circuit; Routine Maintenance Guidelines

Grundig TK 20
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MAINS
VOLTAGE
ADJUSTMENT
If
your
own
Mains
Voltage
Supply
differs
from
that
given
on
the
first
page
of
this
Instruction
Book
(230-250
volts
A.C.)
then
it
becomes
necessary
to
re-set
the
Mains
Voltage
Tapping
Panel,
which
is
found
under
the
top
deck
of
the
TK20
in
the
top
left-
hand
corner.
MAKE
QUITE
SURE
THAT
YOUR
TK20
IS
DISCONNECTED
FROM
THE
MAINS
SUPPLY.
Remove
the
right-hand
knurled
knob
(B)
by
undoing
its
fixing
screw
with a
small
screwdriver.
Lift
off
the
Recording
Level/Volume
Control
(A).
Now
pull
off
the
left-hand
Selector
Switch
(C).
Next
unscrew
the
four
coin
slotted
Brass
Screws
which
still
hold
the
Top
Deck,
then
lift
off
the
Top
Deck
of the
TK20.
The
Mains
Voltage
Selector
Panel
is
in
the
top
left-hand
corner
and
the
different
Voltage
Settings
available
are
marked
on
the
little
square
panel.
Unscrew
the
small
screw
from
its
240
volt
position
and
replace
this
into
the
voltage
figure
closest
to
your
own
Mains
Supply.
The
range
over
which
the
voltage
setting
is
most
effective
is
shown
as
the
first
item
of
the
‘Technical
Specification’
in
this
Booklet.
THE
DIODE
CONNECTION
To
install
the
Diode
Connection
in
your
radio
set,
you
will
need
two
resistances,
one
of
between
1
and
2
megohms
(not
critical)
and
the
other
of
between
50,000
and
100,000
Ohms.
These
are
connected
to
the
Volume
Control
as
shown
in
the
drawing
below
and
then
taken
by
a
screened
lead
to
the
TK20,
preferably
by
a
co-axial
Socket
or
jack
on
the
Radio
Chassis.
If
p.c.
is
present
on
the
Volume
Control,
the
.o25
mfd.
condenser
should
be
added
between
the
Volume
Control
and
the
1-2
megohm
resistance,
and
if
a
very
long
lead
is
used
for
connection
to
the
Radio,
the
35
pf
condenser
should
be added.
When
using
this
system
an
advantage
is
that
the
Input
of the
TK20
is
inde-
pendent
of
the
volume
setting
of
the
Radio.
|
r--4
(-2Ma
|
TO
DIODE
INPUT
as
WY)
OF
TK20
FROM
J
L--4
| 1
Xo
DIODE
|
‘O25yuF
1
r--4
1
ea
1}
|
SCREENED LEAD
TO
AUDIO
35pF
| .
STAGES
OLUME
CONTROL
|
36-100
|
|
Ka
CHASSIS
13
ADDITIONAL
CIRCUIT
MAINTENANCE
After
many
hours
use
you
may
notice
that
sounds
which
should
have been
completely
erased
when
a
new
recording
is
made
are
still
present
as
a
faint
‘ghost’
and
that
reproduction
of
the
higher
frequencies
tends
to
be
weak.
This
is
because
microscopic
par-
ticles
of
tape
are
sticking
to
the
magnetic
head.
The
front
of
the
head
should
be
cleaned
with
a
small
piece
of
wood
such
as
a
match
or
orange
stick,
after
first
removing
the
front
cover
in
front
of
the
sound
channel
(by
pulling
it
upwards).
All
the
head
assemblies
are
then
accessible
and
may
be
carefully
cleaned.
It
is
also
advisable
to
inspect
the
rubber
pressure
roller
to
ensure
that
it
is
clean,
and
has not
accumulated
small
particles
of dust
or
tape.
We
must
point
out
that
your
TK20
Tape
Recorder
is
a very
delicate
precision
instrument
and
on
no
account
should
you
carry
out
any
other
adjustments
or
repairs
yourself.
As
with
all
precision
instruments
it
will
require
a
certain
amount
of
main-
tenance
after
many
hours
of
use
and
this
should
only
be
done
by
a
competent
Service
Engineer.
STANDARD
TAPE
LONG
PLAYING
TAPE
°
000
°
5
050
5
'o
100
io
so
Is
®
200
20
20
250
300
*
25
350
30
30
400
Chart
of
running
time
os0
Feo
for
950
MINUTES
felele)
MINUTES,
Standard
and
L.P.
Tapes
pos.
INDICATOR
14

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