Record Calibrate Alignment; Record Equalization; Erase Alignment; Depth Of Erase - Scully 280B Series Instruction And Maintenance Manual

7-16
Maintenance
7.15 Record Calibrate Alignment
A. Set Monitor switch to PLAYBACK position.
Record 1 kHz.
B. Adjust RECORD LEVEL control on front of
record/playback control panel until front pan­
el vu meter records zero vu.
C. Set Monitor Switch to RECORD.
D. Adjust record calibrate potentiometer R1 on
record/playback amplifier PWA for zero vu.
E. Set Monitor switch to PLAYBACK. Input and
output levels should correspond.
7.16 Record Equalization
A. Before making any record equalization adjust ­
ment, be sure that record bias set and record
calibrate have been performed.
NOTE
Record equalization adjustments
are made at zero vu operating
level or less at 15 in/s, and at -10
vu or less at 7.5 and 3.75 in/so
B. Record 1000 Hz at a convenient reading on
the vu meter.
C. According to the speed selected (high or low)
sweep the oscillator while adjusting REC HI
at the high speed for flattest response at the
upper frequencies and PLAY LF HI at fre­
quencies below 150 Hz.
D. Repeat at low speed using controls marked
REC La and PLAY LF La.
7.17 Erase Alignment
Visually align erase head height to correspond to
record and playback heads.
7.18 Depth of Erase
A. Record a 1000 Hz tone at +6vu (+10 dBm on
voltmeter) for several minutes. Remove input
signal.
Model 280B
B. Rewind tape to beginning of 1000 Hz tone .
C. Connect the output of the machine through a
1000 Hz filter to the ac voltmeter.
D. Place the machine in the Record mode and
check the erase head rotation for proper gap
control.
E. Erase should be at least -75 dB (from +10
dBm) as indicated on the ac voltmeter.
7.19 Signal-to-Noise Ratio
A. Connect the output of the machine through a
weighting filter (ASA Standard S1.4-1961) to
an ac voltmeter.
B. Place the machine in the Record mode with
no signal input. The output should be as fol­
lows (when referenced to +6 vu), after correc ­
ting for the insertion loss of the filter:
TAPE
SPEED
FULL
TRACK
HALF
TRACK
TWO
TRACK
FOUR
TRACK
FOUR
TRACK
0.25" 0.25" 0.25" 0.25" 0 .25 "
30
in/s
72 dB 68 dB
68 dB 68 dB 65 dB
15
in/s
72 dB
68 dB 68 dB 68 dB 65 dB
7.5
in/s 72 dB
68 dB 68dB 68 dB 65 dB
3.75
in/s
68 dB 64 dB 64 dB 64 dB 61 dB
7.20 Distortion
A. Connect recorder input to ACVM and oscil ­
lator.
B. Connect recorder output to wave analyzer.
C. Set oscillator to 500 Hz at +4 dBm.
D. Adjust RECORD LEVEL knob to zero vu
(-10 vu for 3.75 in/s).
E. Set wave analyzer to 500 Hz .
F. Set PLAYBACK LEVEL knob to CAL
position.