Learning Event 9:
DESCRIBE THE PURPOSE AND USE OF HEADS ON TAPE RECORDERS, AND EXPLAIN HOW TO
REPAIR DAMAGED TAPE
1.
Purpose and use of heads.
The total number of heads on a specific tape
recorder/producer will be governed by the actual video, audio, control, and cueing
channels designed into the equipment.
a. Certain helical scan equipment requires a single video record/reproduce
head. There will be a video erase head which wipes the full width of the tape.
b. Normally, an erase head is provided for each of the audio, control, and
cueing tracks. This could be one or two audio, one control, and one cueing.
c. Or, it could be a minimum of one audio and one control. For each of the
required erase heads, there is a corresponding record/reproduce head.
d. The recorder may have as many as 10 heads or as few as 5 heads if one
erase head were used to wipe both the audio and control tracks during recording.
2.
All the heads except the video record/reproduce head are of the fixed or
stationary head design. The only tape penetration by the fixed heads will be a very
minute amount resulting from design, or caused by the wearing and grooving of the
plastic around the head gap.
a. The video record/reproduce head does have a designed head-to-tape negative
clearance of approximately 3 to 4 mils.
This means that the head actually
protrudes into the tape, ensuring contact at all times.
b. If, during operation, the tape is stopped, the head will continue to turn
for only a brief period of time. If the head drum is left in motion and the tape
is stopped, the tape may be cut by the video head as it continues to trace the same
path across the tape.
c. Damage may also be done to the head if the gap becomes clogged with oxide
particles.
This will render the head ineffective for any further use.
If it is
desirable to stop the tape for an extended period of time, then the head drum
should also be stopped or the tension on the tape released.
3.
If it becomes necessary to repair a tape because of some type of damage such
as a broken tape or a crumpled tape which required cutting and splicing, then it is
very important that the tape be spliced precisely (fig 1-20).
a. If the tape is cut on a 90€ angle (fig 1-20c), and all tracks are
precisely aligned, the effect, theoretically, would be a vertical wipe with no roll
or tear visible in the picture.
b. If the tape is cut on the 3€6' angle
(fig
1-20a),
an
instantaneous
transition from one scene to another will occur.
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