Ampex 351 - Page 80

Reproduce Amplifier Noise Measurement
Step 1:
Step 2:
Record Amplifier Erase Current Adjustment
Step I:
8-7
Step 8: Depending on tape speed, tones from
15,000 cycles to 30 cycles now will
be reproduced from the standard
tape. Adjust the appropriate variable
equalizer (2R31 for 7% and 15 ips,
and 2R30 for 3% ) to give the flattest
possible high frequency response.
CAUTION
The equalizers should not be used to
compensate for system deficiencies
(dirty leads, bad alignment, etc.). In
general the playback equalizer should
not be moved more than 2 db from the
standard curve.
NOTE
Catalog #30750 and 30950 electronics
used fixed equalization.
NOTE
If the head azimuth is far out of
alignment (possible if inexperienced
personnel without proper equipment
have attempted alignment proced 
ures) minor peaks may be observed
on both sides of the maximum. The
proper setting is 15 to 20 db higher
than these peaks.
NOTE
When reproducing Ampex standard
alignment tapes on multi-track equip 
ment, the bass end of the frequency
spectrum will rise in response. The
actual amount of rise will vary with
the width and location of the track.
This phenomena is present because
the reproduce head “ sees ” additional
flux on each side of the head at long
After performing the previous align 
ment checks, stop the tape motion.
After the equipment has been prop 
erly installed and connected, and all
POWER switches arc in the ON posi 
tion, thread blank tape along the pre 
scribed path.
89-0144
Issue A
NOTE
Do not change this playback level
setting for the remainder of the ad 
justments
and adjust the left hand stop nut on
the reproduce head for maximum out 
put on VU meter or VTVM. If the
peak is broad adjust for minimum
output variation.
Step 9: Reproduce level control calibration —
The next tone to be heard on the 3%
and 71/2 inch per second standard
tapes is a reference tone at operating
level. Adjust the playback level con 
trol to obtain a zero reading on the
VU meter or a +8 dbm (1.95V) out 
put on a VTVM. On the 15 inch per
second standard tape, all tones are
at operating level, so this calibration
was made in Step 6.
wavelengths since the standard tapes
are recorded across the complete
width of the tape. This fringing effect
is not present when recording a track
the same width as the reproduce
head. The electronics should not be
readjusted to compensate for this rise.
Read the stopped tape noise measure 
ment on the VTVM. Noise should be
below the level specified in perfor 
mance characteristics. Inaudible low
frequency bounce can cause the meter
io read higher than performance
characteristics tolerances. Disregard
these momentary readings because
they arc frequencies far below the
operating range.