,-
C 8 Relay Box
The
relay
box cortalns the control clrcults
for the varlous modes of operatlon.
It ls
mounted
Just
belowthe
tape transport
power
supply.
Aprlnted clrcult board
mounted
onhlnges, carrles nlne
plug-ln
relays type
Slemens
L54 d.
/
93 n. Twelve
plug-tn
power
relays type
SCHRACK,
have
thelr sockets on
the
urderslde
of the relay box. Slllcon diodes
are
used on
all
relay wlndings for
cllck suppresslon. The
relay box
also
carrles the sockets
for
the lnterconnectlng cables to the
varlous sub-assemblies of the
recorder.
A reslstor
(
27O A
/
40
W
)
ls
mounted on the rlght hand
stde
of the relay box.
Four
potentlometers
P I to P4
are
mounted on the
front-slde
of the
relay-box
and
these
are
for
adjustlng
the
starttng and
braklng characterlstlcs of the
recorder.
Each
potentlometer
shaft is
secured
by
a
lock-nut to
avold
accldental alteration
of
its settlng.
The functlons of these Dotentiometers are as
follows:
Start
When
the
"playback"
button ls
pressed,
the mechanlcal brakes
are
released
at
once
ard 220 V
are applied
to the take-up motor ln order
to
accelerate
the tape
as
qulckly
as
posslble.
A.fter a
small
delay, the
pinch-roller
ls
pulled
ln ard thls should happen ldeally when the tape has reach-
ed its
nomlnal speed. Thts delay can be adrusted by
means of the
potentlometer
P l. The best
compromise
wtll be achieved lf the
potentlometer
ls
ad,usted ln
the following manner:
Place
a
thousard meters
(
app. 3,300
ft
)
of tape onto the left hand spooling-plate
ard
wird forward untll the spoollng dlameter on the take-up spool ls 150
mm
(
6
lnches
)
.
When
pressing
the
playback
button, no loop
should
be thrown between the capstan
and
the drlve-pulley of the tlmlng indlcator. The
potentlometer
P
1 should be turned clock-
wlse
until thls is
iust
achieved.
Durlng thls
adjustment,
the
potentiometer
P2
should
be
opened
about
90o
(
clockwtse
).
After a short tlme
the take-up motor
should
be swltched back to lts normal operatlng voltage. For
this
purpose,
the contact whlch
was
short-circultlng
the resistor R
270O
/
40W, whtch
ls in
serles wlth the take-up motor, ls
opened. The
delay-ttme
before thls
contact is
opened
ls ad-
Justed
by
means
of
the
potentlometer
P 2. Thts
should
be
set
up
as
follows
:
The
thousand meter
(
approx.
3,300
ft
)
tape should be
wourd
on untll the remainlng
spoollng
dlameter
on the left hand spool ls down to 150 mm
(
6
lnches
).
When
pressing
the
playback
button
no
loop should appear between the capstan and the
pulley
of the
ttmtng trdtcator. At the same time,
the dash-pot of the tape tenslon balance
should
be
adjusted
(
see also
under C 3
"Tape
TenJion Balance"
)
so as
to
glve
critical damping.
These two
adrustments
are somewhat lnter-dependent and should
be repeated
two or three times
untll optlmum results
are
achieved.
2. Brakes
The braklng
(
see also urder C 2
"Spoollng
Motors
ard
Brakes"
)
ts effected by
applylng
a large
DC braklng current
to
the spoollng
motors for
a short
tlme. The length of tlme durlng whlch thts
braklng current ls applted,
when the machine ls stopped
from
the
"playback"
or
"record"
modes,
can be adJusted by means of the
poterttometer
P 3
.
The length of the braklng tlme ls
approximately
half a secord. The settlng ls
rlght
lf
the tape llft mechanlsm holds the tape
away
from the
heads
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