RCA Victor STR-6 Manual page 6

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FIG.
4
BONOM VIEW
OF
TRANSPORT MECHANISM WITH
MOTOR
AND AMPLIFIER
REMOVED
Recording Bias Voltage
Recording bias
is
obtained
from the oscillator
circuit of V4
and
Ll
and
applied
to the recording sig-
nal at the
head
input.
The
recording bias level
re-
quires
adjustmentonlywhena component
in the oscil-
lator
head
circuit
is
replaced
or
if.
C27 adjustment
is
altered.
To adjust recording bias level, the recorder
must
be
in the cabinet. For location of
adjustments
,
refer to Fig.
3.
1. Depress Monitor
push button and
allow re-
corder
to warm
up.
2.
Connect a calibrated
oscilloscopefrom test
point TP-2 to chassis ground.
NOTE:
Use
a
low-capacity probe
withthe oscilloscope
in order to minimize clrcuit
loading.
The
head, capstan,
and pressure
roller
may
accumulate tape
coating, worn
off
as the tape passes
these
parts.
Clean
the head
surfaces, capstan,
and
pressure
roller
with a soft
cloth.
Never
clean the
recording
head
with a brush, as this
could
mar
the
lamination.
3.
Adjust
C2?
for
an
indication of
1gb
votts peak-
to-peak
on
the oscilloscope.
NOTE: The bias signal is
60
kc
and cannot
be
accu-
rately
measured with
an
audio output meter.
Oscillator Frequency and
0utput
Level
The
oscillator
frequency is
G0
tc t
b kc and
is
obtained by adjusting
bscillator coil Ll.
The
oscillator
output
is
used
for
both
the
re-
cording bias
and erase
voltage.
To adjust recording
bias
level,
see "Recording Bias
Voltage.
"
Erase
voltage requires
no
adjustment,
but should
be
greater
than
500
volts peak-to-peak
as
measured at
the
jun-
ction
C2? and
C31
with
a calibrated
oscilloscope.
NOTE: A low-capacity probe must be
used
with
the
oscilloscope in
order
to
mlnimize circuit load-
ing.
CLEAN ING
der
the
plastic
escutcheon.
The rubber-tired idler
wheels
and
roller
must be
kept
free of oil or
grease.
oil orgrease from
rubber
parts,
use a
soft
alcohol
or
carbon tetrachloride.
Be careful to prevent
cleaning
fluids
moving the
lubricant from Oilite
bearings.
pressure
To
clean
cloth
and
from
re-
Page
6
Occasionally
clean any
foreign matter from
un-