Ampex 200A User manual

INS,TRUCTION BOOK
MODEL 200A
MAGNETIC
TAPE RECORDER
4
-
AMPEX ELECTRIC CORPORATION
SAN CARLOS, CALIFORNIA

Contents ...
Introduction ....
Performance Characteristics
Tape
......
Drive System ....
Head Housing ...
Electronic System ...
Controls .....
Installation and Operation
Adjustments
....
Maintenance ....
Demagnetizing Heads . .
PAGE
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........ 5
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11
12
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INSTRUCTION BOOK No ..... :./~ ...............
ISSUED FOR
AMPEX MAGNETIC TAPE RECORDER No .____ /?- _________.._____
Printed in the U. S. A.
Copyright, 1948, by Ampex Electric Carp.
300-7 - 1 5 -48

INTRODUCTION
The AMPEX Magnetic Tape Recorder has been so designed as to make the highest
quality of recordings possible to achieve. Using the best possible input and monitoring
equipment, recordings cannot be distinguished from original program material when
directly compared. All components have been conservatively designed, using the
best
possible materials, in order to insure maximum reliability of service.
PERFORMANCE CHARACTERISTICS
The specifications of the AMPEX Magnetic Tape Recorder are as follows:
FREQUENCYRESPONSE:
30 to 15,000 cycles - + 1 db.
DISTORTION: Distortion in the overall system (from input terminals to output termi-
nals) at peak meter reading does not exceed
4% intermodulation distortion, using mea-
suring frequencies of
100 and 2,000 cycles with the high frequency attenuated 12 db.
Total r.m.s. harmonic distortion does not exceed
1% overall for any single frequency
from
100 to 6,000 cycles and 2% for any frequency from 30 to 100 cycles.
SIGNAL
TO NOISE RATIO:The noise level of the system is over 60 db. below 100%
modulation. One hundred per cent modulation
is defined as 10 db. above peak meter
reading, at which point total harmonic distortion does not exceed
5%. The noise level is
that signal which exists at the output terminals of the playback amplifier when recording
in the normal manner with the record input terminals terminated in a resistance equal to
the rated source impedance.
It therefore includes record and playback amplifier noise,
any noise caused by bias
or erasing and any stray pickup in the heads. This measure-
ment is made unweighted over a frequency range of
30 to 15,000 cycles and with a tape
that has been previously modulated
100% with a 400-cycle tone.
MONITORING
: Instantaneous monitoring made possible by separate record and play-
back heads and amplifiers.
RECORDAMPLIFIER:Will provide
100% modulation with an input signal between
- 15 d.b.m. and + 20 d.b.m. 150 or 600 ohms input impedance. (Bridging input op-
tional.)
PLAYBACK AMPLIFIER:100% modulation will give an output up to 30 d.b.m. Norm-
ally adjusted for peak output of
+ 4 W (100% modulation gives + 14 d.b.rn.) . Output
impedance 150
or 600 ohms. Adjustment of both high and low frequency equalization
is provided on both record and playback amplifiers by means of screwdriver adjustments.
All gain controls, including erase and bias currents, are also screwdriver adjustments.
CHASSIS
: All chassis of plug-in construction.
HEADS: Plug-in head assembly for rapid changing of heads and to expedite head
Carefully shielded and designed for convenient and rapid threading
Recording and playback gaps critically aligned allowing interchangeability of
30 inches per second for normal playing, over 300 inches per second
exchange service.
of tape.
recordings without high frequency loss.
average during rewind
or fast forward.
TAPE SPEED:
TIMING: Accuracy of playback timing f 0.03 % .
MARKING:A marking device incorporated over the playback head for spotting tape
in editing operations.
3

RECORDING TIME: 35 minutes per reel.
TAPE MOUNTING: On 4-inch diameter hub with single 1Cinch diameter flange at-
tached for safe and convenient handling of valuable program material. Design of driving
spindles allows reels to be placed
on or removed from recorder quickly and conveni-
ently. Hub design permits rapid tape threading.
TAPE
Sufficient reserve capacity and flexibility have been designed into the amplifiers so
that any of the leading makes of tape may be accommodated. However, as shipped the
machine has been specifically set up for the use of Minnesota Mining
& Mfg. Co. type
RR tape, as this tape has been found to give the best signal-to-noise ratio with the mini-
mum modulation noise and other undesirable effects. In general, plastic-backed tapes
are superior to paper tapes, as they are quieter and more uniform in their characteristics,
and have less tendency to sludge and foul the heads.
DRIVE SYSTEM
The drive system consists of three motors: the capstan motor, which is a hysteresis
synchronous motor for driving the tape at a constant speed of
30 inches per second; a
takeup motor
for winding up the tape paid out by the capstan; and a rewind motor,
which provides back tension
on the tape during normal playing and rewinds the tape
after it has been played.
The takeup and rewind reels rest
on turntables attached directly to the motor shafts.
The motors are double ended, and a cast iron brake drum is mounted
on the lower shaft
extension. A band-type brake is employed, the brakes being applied
by springs and
released by solenoids. The brakes are de-
signed to apply greater braking force in the direction of rotation in which the reel pays
out tape,
so that the unwinding reel will always tend to stop the fastest, thereby keep-
ing tension in the tape at all times during stopping. The rewind and takeup motors are
specially designed for the proper torque characteristics during all operating conditions.
Torques are adjusted
so that at no time does the tape tension exceed 12 ounces.
The capstan is a hardened steel shaft mounted in its own bearing housing, and is
coupled to the drive motor through
a flexible coupling. A solenoid operated rubber
idler clamps the tape against the capstan shaft for normal playing speed. The whole
capstan drive assembly is mounted
on a plate which can be tilted to insure optimum
tracking of the tape through the capstan.
These take
up the slack in the tape, smooth out variations in tension, and absorb the shock of start-
ing and stopping. The tension arm on the takeup side is equipped with a micro-switch
or safety switch (S7) which shuts the machine off if the arm is allowed to move to the
end of its clockwise travel. Thus,
if the tape should break or run out, the machine will
automatically shut off. THE SLACK
MUST BE TAKEN OUT OF THE TAPE AND
THE TAKEUP TENSION ARM PLACED IN THE PROPER OPERATING RANGE
BEFORE THE MACHINE WILL START.
5*
This construction is illustrated in Fig. 1.
This assembly is shown in Fig. 2.
The tape passes over a tension arm on each side of the head housing.

HEAD HOUSING
Figure 3 illustrates the head housing with the gate retaining springs removcd so
that the gate is opened to expose the heads. The playback head, which appears on the '
extreme left, is contained in two mu-metal shield cans with a copper shield can in be- ~
tween. Matching coverplates on the gate, consisting of three mu-metal plates insulated 1
with non-magnetic spacers, cover the front of the playback shield cans when the gate is 1
closed to provide completely enclosed shielding. The record and playback heads are 1
each contained in a copper shield can.
iron, which provides further shielding.
removed by loosening the
two captive screws with the crank provided in the machine. ~
The individual heads are mounted by two studs which extend through the top of the '
head housing into a recess which is covered by the nameplate. Removing the nameplate I
on top of the head housing exposes the retaining lock-nuts on the mounting studs. In
the case of the record and playback heads, the mounting is designed to allow vertical
alignment of the head gaps. One side of the head baseplate rests on
two small ball pivot
points, and the other side against a spring. Rotating the locknut on the right hand stud
(when facing the machine) varies the compression of the spring and therefore the align-
ment.
The opening and closing of the gate is cam operated from the handle on the
rear
of the head housing. Tape guides on the inside of the gate hold the tape at the proper
vertical position. When the gate is open, the tape is removed from contact with the
heads. The position
of the guides is such that when the gate is closed, the tape makes
a slight wrap around each head.
The head housing and gate are malleable cast
The head housing is a plug-in unit, and is
ELECTRONIC SYSTEM
The electronic system consists of the record amplifier, playback amplifier, power
supply, and relay chassis for controlling all operations. All four chassis are
of the
plug-in type, mating with plugs in a wiring gutter in the back. All external connec-
tions are made to receptacles provided in this gutter, which are made available by remov-
ing the panel in the back of the cabinet. The entire chassis assembly is resiliently
mounted to protect from shock during shipping and to isolate the amplifiers from vi-
bration.
To remove a chassis, use the crank provided in the clip
on the left hand (when
facing cabinet) inner wall
of the cabinet.
1. Loosen hold-down suews at the front of the chassis bottom plate (and remove
head connector cables in the case of record
or playback chassis).
2. Insert crank in the Allen head screw in front under chassis, and rotate clothwise
as far as it will go. (See Fig. 4.)
3. Lift handle to disengage bottom plate from drive pin and pull chassis out.
To replace chassis, slide chassis in proper ways until drive pin engages in the hole
provided in the front extension of the bottom plate. Turn crank
counter-clockwise as
far as it will go, and tighten hold-down screws.
It is necessary
for pins
9 and 10 on the remote control connector to be jumpered before the machine
can
be started. This jumper is provided in the mating plug furnished with the machine.
Fig.
14 is the wiring diagram for the remote control panel.
Connections for remote control are provided on the wiring gutter.
8

POWERSUPPLY: The power supply diagram is shown in Fig. 8. It consists of a 360
volt supply for the erase, bias, and playback output tubes plate voltage, and a regulated
300 volt supply for the record and playback amplifiers, the oscillator, and erase and bias
screens. In addition, there is a
D. C. filament supply for the playback amplifier, a 36
volt A. C. output to provide 24 volts D. C. for all relays and solenoids, and filament sup-
ply for all tubes.
RELAYCHASSIS: The relay chassis wiring diagram is shown in Fig. 9. This chassis
contains
a selenium rectifier for the 24 volt D. C. supply, and all relays. The operation
of the relays is shown schematicallyin Fig. 12, and explained below under CONTROLS.
RECORD AMPLIFIER: The record chassis, Fig. 10, contains the record amplifier for
matching
a 150 or 600 ohm line and converting the incoming signal to constant current
in the record huad, a
60 kc. oscillator, and separate power amplifiers for providing 60
kc. bias and erase currents.
The record amplifier is provided with screwdriver adjustments for gain and quali-
zation
so that different machines can be adjusted to have identical characteristics. The
general method of overall equalization is to boost both high and low frequencies during
recording, and attenuate as necessary on playback. The low and high frequency con-
trols are set to give flat overall frequency response, and each machine is checked
to
match a standard tape to insure that recordings will be interchangeable among machines.
One stage
of amplification is provided in the triode, V301. A 6AC7, V302, is used
on the output as a current converter. The transformer T302 operates as a current trans-
former to further increase the record current, and the record current is fed
back
through the cathode of the output tube V302 to decrease distortion and flatten the fre-
quency response. The record amplifier is capable of producing five times
as much un-
distorted signal as is necessary to fully modulate the tape.
The oscillator tube
V303 uses a high Q tank circuit to provide excellent wave form,
and drives
V304 to provide bias current and V305 for erase current. The bias put ut
is tuned to the record head by means of trimmers C317 and C318 for minimum noise.
The erase output is matched to the erase head with trimmer
C319, which is also tuned
for minimum noise. The oscillator plate voltage and bias and erase
tube screens are
supplied from the regulated 300 V. supply.
PLAYBACKAMPLIFIER (Fig. 11) : The playback amplifier is designed to operate
directly from the playback head, and contains the necessary amplification and equaliza-
tion to provide flat frequency response and a maximum output level of
30 DBM into
a
150 or 600 ohm line from a fully modulated tape.
The playback head output is fed directly into a pentode stage,
V401. This is fol-
lowed by an equalization network to compensate
for the voltage characteristic of the
playback head.
R406 in series with capacitor C404 provides 6 db. per octave attenua-
tion up to around
4,000 cycles, where the response is leveled out by R407. With high
and low frequency controls
R430 and R431 respectively all the way up, the overall
response is boosted at both ends. These controls are therefore set to give flat overall
response, and are screwdriver adjustments. The low frequency control is normally set
at the minimum position
(all the way counter-clockwise) for best overall signal-to-noise
ratio.
Machines starting with serial number
20 are equipped with a different kind of play-
back cable which extends the range of the response. With this cable, an additional
A
- -
10

arm consisting of C419 and R432 is necessary to flatten the response. When different
head assemblies are used, it may be necessary to slightly alter the value of
C409 and/or
C419 to keep the response within
C414 and C415, in conjunction with L401 and L402, provide a 60 kc. wavetrap
to remove the bias and erase frequency from the playback output.
C414 and C415 are
air trimmers with screwdriver adjustment.
The first
two stages of the
amplifier are resiliently mounted. The first stage tube,
V401, is selected for low noise
level and low microphonics. Of the five
12SJ7.s in the amplifier, at least two or three
are satisfactory for the first stage.
This pad
plugs into the octal socket provided on the rear wiring gutter. Since the maximum
operating level of the playback amplifier is
30 dbm. without distortion, the gain setting
should
be such that the peak output level plus the loss in the pad provided does not
exceed
20 W. This setting will allow 10 db. for transient peaks without distortion.
The machine is normally adjusted for a peak output level of + 4 W.
1 db.
All tubes except the output stage are D. C. heated.
An isolation pad is provided on the output of the playback amplifier.
co NTR
0 LS
The following controls are provided:
1. Start, which provides normal playback at 30 inches per second.
2. Record.
3. Fast forward, for shuttling the tape in the forward direction at high speed
(more than
10 times playing speed).
4. Rewind, for rewinding the tape at high speed (more than 10 times playing
SPd)
*
5. stop.
None
of the controls can be operated unless the Start button is first operated. When
it is desired to start the machine in any of the other conditions, the Start button must
be operated simultaneously with the desired button. Once the Rewind
or Fast Forward
button has been operated, it is necessary to depress the Stop button to select another
mode
of operation.
The operation of the controls can
be followed in the schematic control diagram, Fig.
12. When the power is turned on, the power supply and all filaments are energized.
Plate voltage is connected to both record and playback amplifiers. The record head,
however, is disconnected from the record amplifier by the normally open contacts
K204-2,
and the record output is grounded through the normally closed contacts K204-2, which
also charges condenser
c315 and thereby prevents a current pulse through the record
head when the record head is connected to the ouiput. The stop light is energized
through normally closed contacts
K201-2.
Depressing the Start button provides normal playback operation. The brake solenoids
pick up, extending the brake springs and releasing the brakes, the capstan solenoid
picks up, clamping the tape against the capstan, relay
K201 picks up through the nor-
mally closed Stop switch contacts, providing the tape has been pulled up to swing the
takeup tension arm into normal playing position, which leaves the safety switch
S7
contacts closed, When relay K201 picks up, it locks in the start switch and energizes
the capstan, takeup, and rewind motors. The takeup motor is energized athsvolts
through resistor
R202, while the rewind motor provides holdback by being energized
11

at @ volts through R203. The time relay K205 is picked up, the start light is ener-
gized, and the stop light disconnected.
Pressing the record button picks up the record relay K204, which locks itself in,
energizes the record light, connects the record head to the record amplifier output,
and supplies plate voltage to the oscillator, bias and erase
tubes. All motor connections
remain the same.
Operating the Rewind button picks up relay K202, which
locks itself in, energizes
the Rewind light, applies
90 volts to the rewind motor through resistor R205, energizes
the takeup motor at 30 volts through R201, and disengages the capstan solenoid from
the capstan, allowing the tape to move at high speed. The record relay K204 is also
dropped out, and the Fast Forward relay is locked out.
Depressing the Fast Forward button causes relay K203 to pick up and
lock itself
in, energizes the Fast Forward light, applies
90 volts to the takeup motor, energizes
the rewind motor
at 30 volts through R201, and disengages the capstan solenoid. The
record relay is dropped out (or locked out), and the Rewind relay is locked out.
When the Stop button is depressed, relay K201 drop out, which drops out all
relays, solenoids, and motors. De-energizing the brake solenoids allows
the springs
to apply the brakes to the rewind and takeup reels. Relay K205 does not drop out for
over one second because of the condenser c204 across it which holds up the voltage.
Thus for
a brief moment D. C. is applied to the capstan motor, which stops the capstan.
While there would
be no harm in leaving the D. C. on the capstan motor all the time
the machine is not running, the time delay relay is provided to disconnect the
D. C.
after the motor stops, to eliminate the audible hum of the motor due to the unfiltered
D. C. source. Stopping the capstan shaft is necessary to allow immediate restarting
without throwing a loop of tape.
(Note: Because of procurement difficulties, it has not always been possible to use
the same make of motors. Motors of different manufacture may require different re-
sistors and voltage settings. The above description applies to Electric Indicator motors.
Motors manufactured by Bodine Electric Co. require a resistar in series (R205) during
Fast Forward and Rewind operations to drop the voltage on the motor taking up the
tape to 85 valts. Proper settings during normal playing are
60 volts on the takeup
motor and
55 volts on the rewind motor.)
INSTALLATION AND OPERATION
To install the machine, remove the back panel and connect power, input, output,
and remote control (if required) cables to the plugs provided.
To operate the machine, the roll of tape is placed on the rewind turntable, which
is the one
on the left when facing the machine. The recommended threading procedure
is the “straight through” method in which the tape is passed behind the rewind idler
tension arm guide, around the rewind idler, through the head housing, between the
capstan and capstan idler, over the takeup tension arm and thence to the takeup
-1.
To thread the tape on the takeup reel, form a small loop at the end of the tape as
shown in Figure 5, slide the loop over one of the drive pins and pull both sides of
the loop through the slot opening. If the end of the tape is on the side toward the
front of the machine, rotating the
reel countercldwise and putting tension on the tape
will automatically cinch the tape.
When the slack is taken out of the tape and the
12 .

takeup tension arm moved into position, the machine is ready to start. When recording,
it is recommended that plenty of leader
be used to facilitate cueing and allow for
breaking
off of the ends.
Due to'the fact that some lots of tape have
been cut crooked and do not wind prop-
erly, it is recommended that when winding at higli speed (Rewind or Fast Forward), a
cover plate be used on the reel taking up the tape. For this purpose, a flat aluminum
disc is provided. This is placed over the empty reel after threading, and is held in
place by the editing knob. When a factory wound roll of tape is used, the tape should
be played entirely through before rewinding, as the factory winds the tape against the
flange and any unused portion will not furnish proper support if tape is wound back
on top of it in the machine. It has
been found with some tape that if factory wound
rolls are immediately wound in Fast Forward, there are kinks and strains in the tape
which prevent it from snugging up tight and therefore produce a very loose, unsatis-
factory wind. Usually by the time such rolls are rewound once or twice these strains
are relieved and the tape will pack properly. Playing through the roll in normal play-
ing position also produces a satisfactory pack.
To facilitate editing, knobs have been provided to use on each reel so that sections
of tape can be conveniently passed back and forth through the head housing
by hand
to locate specific points in the program. A plugged hole is provided in the gate in
front of the playback head (see Fig.
3), through which a china marking pencil can be
inserted to mark the tape.
To locate a specific point in the program, the usual pro-
cedure is play the tape through and identify the desired spot. This spot is then played
through again and the machine stopped as soon as the desired spot is heard. The tape
is then turned back
by hand, until the spot is right over the playback head, at which
point it can
be marked. When a great deal of editing has been done, it is recom-
mended that the roll be wound completely through once before storing to eliminate
non-uniform tensions in the roll which might cause buckling.
The
first note of the program is placed over the playback head as described above.
A mark
is then made on the tape reel on the rewind side opposite some reference point such
as the finger recess in the guard plate.
The reel is then wound back three complete
revolutions, which with a
full reel allows about five seconds cueing time. The machine
is then started, and the time until the program starts measured with a stopwatch or any
convenient second hand. The time is noted, and the program then reset in the same
manner. The start button is then depressed at the measured time interval before it
is desired to start the program. The above procedure
is independent of the individual
starting time of the machine. Since the machine comes up to full speed in approxi-
mately two seconds, five seconds pre-start time has been found quite satisfactory.
To place two machines in synchronism, the machine to be synchronized is started
slightly ahead of the one carrying the program. The Stop and Start buttons are then
operated in rapid succession, which cause the machine to drop slightly behind. This
is done until the two are in perfect synchronism. In the event the machine is accidentally
dropped too far behind, place
in Fast Fdrward until it is once more ahead.
The following procedure has
been found to be quite satisfactory for cueing.
ADJUSTMENTS
All adjustments have been made at the factory for the correct values, and, with
the exception of record and playback gain, should not
be altered unless damage in
14

shipment or changing conditions indicate that changes are necessary. Adjustments
should
be made only by competent technicians, and only with the proper tools and
instruments to insure that optimum conditions can
be obtained.
ELECTRICAL
:
RECORDCHASSIS :
1. R321, Record gain. Set to give optimum performance at line level of plus 4 VU.
TO set record level for any other value, record desired level at approximately 1,000
cycles. Adjust record gain until playback is plus 4 dbm.
2. R320, Low Frequency Equalization. Set for flat overall response.
3. R319, High Frequency Equalization. Set for flat overall response.
4. R323, Erase Current. Set at maximum.
5. c319, Erase Current Trimmer. Set for minimum erased tape noise. With this
trimmer properly tuned, and with the record head disconnected, the erased tape noise
should
be no greater than the amplifier noise, both audibly and by meter. The char-
acter of the tape noise should
be a smooth hiss. If the trimmer is improperly tuned,
the tape noise will have a “rushy”
or roar character and will be considerably higher
than the amplifier noise. At the factory the
60 kc. tuning unit has been tuned to bring
the oscilIator frequency within the range
of this trimmer.
6. R322, Bias Current. Set for maximum undistorted signal output. In general,
this setting is not critical, once the minimum value is exceeded, which is that value
that gives maximum output
for constant record input. Increasing the bias above this
point does not alter the maximum undistorted signal output, although it takes greater
record current to give the same undistorted signal outpur with higher bias. In general,
the bias is
set above the point of maximum response (15 to 20 milliamps) , to insure
that it will never drift into the tegion of distortion. The bias current can
be measured
by inserting a 1O-ohm resistance in series with the return lead from the record head
and measuring the .voltage across it with a vacuum tube voltmeter. Thus one side
of
the meter is at ground potential.
C317 and c318, Bias Current Trimmers. These trimmers are
set for minimum
tape noise when the record head
is connected and recording zero signal. When prop-
erly set, the tape noise should
be only slightly greater than when the record head is dis-
connected, and the nature of the sound should
be a smooth hiss. It will sometimes
be found that these trimmers will not tune out the tape noise if the bias current is too
low.
PLAYBACK AMPLIFIER:
R429, Playback Gain. Set for
-6 dbm. output from standard tape, or for gain of
unity through the system,
so that when making an A-B test, levels are matched (plus 4
W output with 16 db. pad). Far any other level below 20 W, insert proper pad in
the gutter. R323 may
be used as a fine adjustment, but should not be set to exceed 20
VU output with a zero loss pad.
7.
8.
9. R431, Low Frequency Equalization. Set at minimum.
10. R430, High Frequency Equalization. Set
for flat overall response using
11. C414 and C415, 60 kc. Wave Trap. Set to eliminate 60 kc. from output of
standard tap.
pIayback amplifier.
15

RELAYCHASSIS :
ward and Rewind, respectively.
voltage of 65-70 volts (60-65 volts with Bodine motors).
voltage
of 60-65 volts (55-60 volts with Bodine motors).
Forward respectively.
12.
13.
14.
R201; Adjusts holdback voltage on rewind
or takeup motor during Fast For-
R202; Adjusts voltage on takeup motor during normal playing. Set for motor
R203; Adjusts voltage on rewind motor during normal playing. Set
for motor
R205
; Adjusts voltage on rewind and takeup motors during rewind and Fast
Set for
30 volts.
15.
Set for 90 volts (85 volts on Bodine motors).
MECHANICAL
:
1. Brakes.
The brakes on the rewind and takeup assemblies are energized by
springs, the tension in which can be adjusted by turning the locknut on the bolt to
which the spring is anchored. The brake adjustment is pointed out in Fig.
1 and Fig. 7.
The brakes are set for 16 ounces pull on an empty reel hub (24. 02. in.) in the non-
energizing direction and 32 ounces pull in the energizing direction. The most severe
check
on the brakes is to stop the machine just after it has come up to speed when
starting to fast wind a full
roll of tape. This is the point at which there is the greatest
tendency to produce slack because of the large mass of the unwinding reel. It may
sometimes
be found necessary to tighten the brake on the rewind side slightly greater than
the above figures to prevent slack from forming at this point.
The drive assembly plate is attached to the main
base plate at three points,
two of the points being anchored on spherical surfaces and
the third being spring loaded to allow vertical motion. The spring loaded one is the
one on the right hand side when facing the drive assembly, and is pointed out in Fig.
2.
Turning the locknut on this side adjusts the tilt of the drive assembly. This adjust.
ment has been made to provide optimum tracking of the tape through the drive system.
When properly aligned, straight tape should wind in the middle of the reel hub
1/16
inches above the reel flange. If changes in this adjustment are made, the alignment of
the playback head should be re-checked, as the angle at which the tape passes over the
playback head may be affected. The record head is not affected by this adjustment.
Capstan Idler Pressure Adjustment. The shaft to which the capstan idler arm
is attached is held in a clevis below the mounting plate, as may
be seen in Fig. 6.
Loosening the clevis as shown in Fig. 2 allows the arm to be rotated. To make this
adjustment, the idler is held firmly against the capstan at the same time that the solenoid
is seated, and the clevis tightened at this point. Care must
be taken to insure that the
solenoid is seated. On machines of serial numbers
1 to 22, inclusive, the solenoids have
a double winding, and seating the solenoid disconnects one of the windings. If the
pull-in winding is 'allowed to remain
on, the solenoid will draw excessive current and
overheat. The capstan idler must
be firmly clamped against the capstan shaft during
playing,
or the system will be seriously subject to disturbances on the rewind reel, ten.
sion arm,
or idler.
The record and playback heads are critically aligned at the
factory
so that recordings may be played back on different machines without affecting
the high frequency response. In general, it is recommended that the head alignment be
left to the factory, where proper instruments and techniques insure proper alignment.
16
2. Capstan Tilt Adjustment.
3.
4. Head Alignment.

However, if for special applications it is desired to change the head alignment, the pro-
cedure for realignment is outlined below.
Remove the name plate in the top of the head housing. The record and playback
heads are tilted
by turning the right hand locknut for each head. The heads are aligned
from a standard tape which has been recorded with a head the gap of which has
been
critically aligned perpendicular to the axis of the tape. The standard tape is recorded at
a signal level
10 db. below peak meter reading with the following sequence of fre-
quencies, each lasting for a duration of approximately
10 seconds. Each frequency is
preceded by a corresponding number of taps to point out the number of thousands, hun.
dreds, or tens of cycles, which can readily
be observed if the output of the machine is
fed into a monitoring system as well
as a meter.
15,000 1,000
14,000 700
13,000 500
12,000
300
11,000 200
10,000 100
8,000 70
5,000 50
2,000
30
The procedure is to play the standard tape and adjust the playback head for maximum
response at one of the highest frequencies. The response should
be observed over the
entire upper range for uniformity, as it is possible to obtain a maximum on a multiple
wave length of a single frequency which will cause dips at other frequencies. After
the playback head has been properly aligned, insert a blank tape and record a high
frequency of
12,000 to 15,000 cycles and align the record head for maximum playback
response. Sweep back and forth with the oscillator to check other frequencies. When
making frequency response checks, use an input level of
10 db. below peak mete!
reading
(-6 dbm. for factory adjusted machine). Otherwise, the tape will be over-
loaded at the high frequencies because of the pre-emphasis characteristic of the record
current.
If it becomes necessary to play material recorded with a head that is not in align-
ment with the AMPEX machine, the playback head can
be tilted for maximum high
frequency response.
TO
realign the playback head with the record head, record a high frequency run and align
the playback head for maximum response as described above. It is recommended that ''
the record head never be tilted if it is possible to avoid it, as this can be retained as the
standard of alignment.
This
is generally quite satisfactorily accomplished by ear.
MAINTENANCE
The following maintenance schedule is recommended :
1.
A. DAILY:
Inspect surfaces of heads to make sure that they arc clear of any deposit. The
region adjacent
to the gap should show a high polish. Heads may be cleaned with a
toothbtush or similar brush, using carbon tetrachloride or alcohol. To allow 8reater
accessibility to the heads, the $ate can
be opened wider by simply pushing forward with
the fingers when in
the open position.
19