Akai M-9 - VII. AMPLIFIER ADJUSTMENT; ADJUSTMENT OF RECORDING BIAS FREQUENCY; ADJUSTMENT OF RECORDING BIAS VOLTAGE

1.
ADJUSTMENT OF RECORDING BIAS FREQUENCY
OSCILLATOR CIRCUIT
BIAS HEAD
OSCILLOSCOPE AUDIO FREQUENCY
OSCILLATOR Fig. 1
Put on the resistor 10 or 50 ohms in series with the Bias Head and connect the Vertical Input Terminal of the Oscilloscope
to points (a) and (b).
Feed
in
the
sine
wave
signal
from
an
Audio
Frequency
Oscillator
to
the
Horizontal
Input
of
the
Oscilloscope
and
tune
the
Dial of the
Audio
Frequency
Oscillator
until
the
Oscilloscope
displays
a circular or
linear
pattern.
Then read the figure on the Dial of the Audio Frequency Oscillator.
If it reads 60K Hz +5K Hz, the Recording Bias Frequency is correct.
If it is not correct, it may be adjusted by inserting another condenser (C405) value 9,000 PF.
ADJUSTMENT OF RECORDING BIAS VOLTAGE
R404 100
Fig. 2
Connect the V.T.V.M. to the point (A) and adjust the recording bias voltage by turning the V.A.C. in the bias oscillator cir-
cuit until it reads the voltage stamped backside the head assembly.
Note:
There is no way of adjusting the erasing bias voltage, but the correct bias voltage is between AC 60 V and 80 V.
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