Ampex 351 - Page 59

Step 7:
Step 8:
Step 2:
Step 3:
Step 4:
Step 5:
Step 6:
Step 1:
)
Capstan idler pressure measurement
6-11
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LOOP OF TWINE AROUND SHAFT
NYLON TWINE
SHAFT
IDLER AT INSTANT
IT LEAVES CAPSTAN
scale should indicate tape tension as
P/2-3 ounces.
Step 13: Use the procedures in the preceding
steps to check and adjust the take-up
tension which is set at R503 (note
that the reel on this side will move
coun terclockwise ).
REEL GUARD
— TURNTABLE
_____ KNOB
Tape
Width
inch
Now wind the twine on the hub by
rotating the reel counterclockwise;
pull, and take a reading. The turn 
table will rotate clockwise.
Repeat the entire process on the take 
up turntable.
Direction of Least
Resistance — Supply
Clockwise — Takeup
Counterclockwise
2.1 ratio ±1 ounce
in accordance with
High Side
89-0131
89-0144
Issue A
Brake Adjustment
Brake adjustment is made (with no power
applied to the equipment') at the point shown
in the illustration.
Step 1: Place an empty 101/2 NAB reel on the
tape supply turntable.
Make small loops at both ends of a
thirty inch piece of nylon lacing twine.
Attach one loop to the tape anchor
on the reel hub and the other to a
0-16 oz. spring scale.
Manually rotate the reel clockwise
to wind several turns of twine onto
the hub.
Pull the scale, making certain that
the twine docs not touch either flange
of the reel. The turntable will rotate
counterclockwise. Take a reading
only when the turntable is in steady
motion, because the force required
to overcome the static friction will
produce a false and excessively high
initial reading.
Adjust the supply and takeup motors ’
brakes for scale readings listed below.
Points of adjustment are shown by
illustration.
NOTE
In the course of normal operation in
the reproduce or record modes, the
SPRING SCALE READING
Direction of Most
Resistance — Supply
Counterclockwise
Takeup Clockwise
12 to 17 ounces
Capstan Idler Pressure
The capstan idler is forced against the cap 
stan by the action of capstan solenoid K501.
Idler pressure is supplied by the capstan idler
pressure spring, and is adjusted by a lock nut
on the capstan solenoid spade bolt. See the
illustration. Tightening the lock nut increases
idler pressure until a point is reached where
the solenoid will not bottom. At this point, idler
pressure drops to a value which is inadequate
to permit the capstan to drive the tape, and
slippage will occur unless the nut is backed
off. Excessive pressure also throws an unnec 
essary load on the upper sleeve bearing, of the
drive motor. The recommended procedure for
adjusting idler pressure is as follows:
Hold the take-up arm so that the
safety switch is activated.
Step 2: With the POWER switch in the ON
position, press the PLAY button, and
note whether the capstan solenoid is
bottomed. (The capstan idler can be
pushed off the capstan easily by
pushing on the idler arm, if the solen 
oid is not bottomed). If necessary,
back off the lock nut until the solen 
oid does bottom at 90 volts a-c when
cold, or 105 volts when warm (after
I/2 hour running). The pressure
( “ dig ” ) against the capstan shaft
should be approximately 5 pounds.