Roberts A-901 User manual

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I Hour
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GENERAL INFO RMAT ION
Roberts Models 90, 90-S, and 90-C tape recorders consist of two basic sections -- a
tape-transport mechanism and a record-playback amplifier.
The Model 90 is a monaural tape recorder. Models 90-S and 90-C are stereo tape re-
corders. Stereo can be recorded by connecting a Roberts Model A-901 stereo amplifier to
jack 2 on the stereo tape recorders. On the Model 90-C, a preamplifier is included for the
lower channel.
The mechanical controls are interlocked to prevent accidental selection of an incorrect
operating mode. r
The Roberts tape recorders have two speeds, 7 L/ 2 and 3 3/ 4 ips. With both monaural
tracks, the recording times are as follows:
Reel Size
5" (600 ft. )
?" (1200 ft. )
3 3/4Ips
I Hour
2 Hours
These models are designed to operate on 60 cycles, lI0-120 volts AC only.
Supplied by:
Roberts Electronics, lnc.
1028 North La Brea Avenue
Hollywood 38, California
This msterial compiled and pvblished by
HOWARD \f. SAtnS & CO., lNC., INDIANAPOtIS 6, INDIANA
cQ40?
Copyright 1960 . All Rights Reserved
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l.
2.
Remove lid from camying case.
Remove microphone and AC supply cord from
storage compartment on left side of canying
0n-0ff Switch
On the Model g0, t}is is a 2-position switch.
When it is in the On position, power is turned on to
the amplifier and tape deck. On the Models g0-S and
90-C, it is a 3-position switch. When the switch is
pushed to the AII On position, power is turned on to
the amplifier and tape deck. When it is in the Amp Off
position, power is applied to the tape deck only. The
Off position turns the power off to the entire unit.
Vol ume
Turning this control clockwise increases the
volume in either record or playback. Turning it
counterclockwise decreases the volume in either re-
cord or playback.
Tone
This control firnctions inplayback only. Turning
it clockwise from position 5 will increase the treble
response; turning it counterclockwise from position b
will attenuate tie response.
Play-Record and Record Lock
This is a 3-position control: Stop, play, and
OPERAT ING
Threading the Tape
l. Place a full reel of tape on feed reel spindle
(6?), making certain the reel slots engage the
protrusions on the pan. place an empty reel
on take-up spindle (2?), again making certain
the slots engage the protrusions on thJpan.
2. Unwind about 14 inches of tape from the supply
reel. Hold a section of tape taut and insert into
the tape slot, making sure the dull-coated side
faces the rear of the recorder.
3. Insertthe freeendof thetape intooneofthe slots
inthe hub of the take-up reel. While holding the
end in place, turn the reel two orthree times to
secure t}te tape to the reel.
To Make a Monaural Recording
I. P-lug a microphone into the Microphone jack, or
place a signal from some other sburce into t}re
Line Input jack.
2. Depress the Record Lock and simultaneously
turn the Play-Record control to ttre Record po_
sition.
3. Adjust the Volume control until the average
reading on the VU meter is -b.
Page 2
P REPAR ING FO R O PERAT ION
case.
3. Make certain all
tion- controls are in the Stop posi-
FUNCTIONS OF CONTROLS
Record. Turning this control clockwise from the Stop
position places the unit in ptay. Depressing the Record
Lock and turning the control to the Record position at
the same time, places the unit in Record.
NOTE: This control is interlocked with the Wind-
Rewind control. It must be in the Stop position
bef ore ttte Wind -Rewind c ontrol can be op e rated.
Wind-Rewind
Turning this controlto the left places tlreunit in
ttte Wind position; to the right, in the Rewind position.
NOTE: This control is interlocked with the play-
Record control. It must be in the Stop position
before the play-Record control can be operated.
Pause
When this lever is raised, pressure is removed
from the drive capstan, and the take-up reel is dis_
engaged. This permits spot editing and momentary
stops.
NOTE: This control is not on the Model g0.
INSTRUCTIONS
CAUTION: Do not connect a speaker or other low-
impedance load to the Output jack while making
a recording.
To Make a Stereo Recording
l. Connect the interconnecting cable from the
Channel-2 head jack to the stereo channel inthe
Model 4-901 amplifier.
2. Move the On-Off switch on the tape recorder to
AII On. Move the On-Off switchon theamplifier
to On.
3. Turn the Volume control until the VU meter
reads -5.
4. PIug microphones into the Microphone Input
jacks, orplace signals from another sourceinto
t}te Line Input jacks.
5. Depress the Record Lock and simultaneously
turn the Record-play control on the tape trans_
port to Record.
6. PlacethePlay-Record switchon A-g0Iamplifier
in Record.
?. On Model 90-C, turn the switch on the built_in
preamplifier, on bottom of the case, to Out.

FIG. I TOP VIEW OF MECHANISM WITH ESCUTCHEON REMOVED.
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It/lonaural Playback
1. Thread the tape (see "Threading the Tape").
2. Turn the unit on and allow a few seconds for it
to warm up.
3. Turn the Play-Record control to Play.
4. Adjustthe volume andtone to thedesired listen-
ing leveI.
Stereo Playback
l. Thread the tape (see "Threading the Tape").
2. Turn the tape recorder switch to Alt On. Turn
the A-90I amplifier switch to In.
3. Connect the interconnecting cable from the
Channel-2 jack of the tape recorderto the Stereo
jack on the amplifier.
4. Make certain the Play-Record switch on the
amplifier is in Play.
5. Turn the Play-Record controlon the tapetrans-
port to Play.
6. Adjust theVolume controls onthe tape recorder
and amplifier to a balanced output.
Speed Change
To change the tape from 7 V 2 to 3 3/ 4 ips, re-
move the thumbscrew and bushing from the capstan.
When the bushing is not being used, store it on the
bushing post.
lndex Counter
After atape is threaded onthe recorder, set the
Index Counter to "000". The index numbers can then
be noted at the beginning of each selection, for future
reference.
External Speaker
An external speaker may be plugged into the
Output jack. The internal speakerwill be fusconnected
when using an external speaker.
Erasing Tape
To erase one track of a tape, turn the knob on
top of the head clockwise. This raises the erase head
tothe half-track position. To erase both tracks at the
same time, turn the knob counterclockwise. This
Iowersthe erase headto the full-track position. When
the unit is in the Record position, the erase head is
automatically positioned before a new recording is
made. To erase the tape without putting a new re-
cording on it, turn the volume to minimum and the
Play-Record control to Record.
To Use the Second Track (ltylonaurall
l. Turn the Play-Record control to Stop.
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Page 3

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2.
3.
Remove the reel containing the tape, and place
it on the left (supply) reel spindle.
Place the empty reel on the right (take-up) reel
spindle.
To Remove Tape Transport Mechanisn from Case
I. Remove the two screws in the spindle pans (one
in each pan),
2. Remove the two screws holding t}le dress plate,
and remove the dressplate.
3. Remove one screw on the right side of the es-
cutcheon and the 7 V2-tps bushlng from the left
side.
Remove the pressure roller.
Remove the Play-Record and Wind-Rewind
knobs.
Remove the escutcheon.
Remove the four screws holding the tape trans-
port to the case.
Unplug all connections to the tape transport and
speaker, and lift the tape transport from the
case.
9. To reassemble, reverse the foregoing proce-
dure.
To Remove Amplifier from Case
l. Remove the four screws holding the amplilier
and escutcheon to the case.
2. Unplug all connecting plugs.
Record-Playback Head Alignment With Standard
Alignment Tape
l. Thread the tape (see "Threading the Tape").
2. Connect a 0.5-volt AC voltmeter to a standard
phono plug, and insert the plug into the Output
jack.
3, Turn the Tone control to maximum.
4. Remove thetwoscrews fromthehead cover, and
remove the head cover.
5. Insert a screwdriver, through the hole in the
head shield, into the alignment screrr.
6. Play back thetape at full volume, and rotate the
4. Thread the tape, and proceed with the recording
as described under "To Make a Monaural Re-
cording. "
D ISASSEMBLY
ADJUSTMENTS
LU BR ICAT ION
Lift the amplifier from the case.
To reassemble, reverse the foregoing proce-
dure.
To Renove Prean:p fron Case on A4odel 90-C
l. Remove the two screws from the bottom of the
case,
2. Unplug aII connecting plugs.
3. Lift the preamp from the case.
4. To reassemble, reverse the foregoing proce-
dure.
To Remove Model A-901 Anplifier fron, Case
l. Remove the four screws holding the amplifier
to the case.
2. Remove the four screws holding the speaker
cover on,
3. Disconnect the speaker.
4. Feed theAC cord throughthe hole inthe storage
compartment.
5. Lift ttre amplifier from the case.
6. To reassemble, reverse the foregoing proce-
cure.
3.
4.
4.
5.
6.
't -
8.
alignment screw in either direction until the
10,000-cycle note givesthe highest meter read-
ing.
Record-Playback Head Alignment With Con mercial
Music Tape
1. Thread the tape (see "Threading the Tape").
2. PLay back the tape at a normal listening level,
and adjust the head alignment screw for maxi-
mum clarity of high-pitched instruments.
Brake Shoes
When brake shoes (34) and (80) become worn,
loosen the mounting screws and rotate the shoes a
few degrees until a new braking surface is exposed.
Lubricate the following parts every three months
Page 4
in heavy service, every six months in moderate ser-

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vice, or once a year in light service, as follows:
l. Feed and take-up reel spindle shafts, with two
drops of light machine oil on each shaft.
2. Rewind idler bearing and wind take-up idler
bearing, with two drops of Iight machine oil on
each bearing.
3. Apply a liberal amount of light machine grease
to drive idler bearing bore.
Saturate thefelt washer in the chrome retaining
cup of.the drive capstan with light machine oil.
Apply a liberal amount of light machine grease
to each roller on all levers and cams.
Themotor bearings are lubricated andsealed at
the factory and need no further lubrication.
4.
5.
6.
Most defects, other than wear or breakage, can
be traced todirty surfaces. The recording head, cap-
stan, and pinch wheel (4) may accumulate tape coating
residue, which is worn off the tape as it passes these
parts. Remove this accumulation periodically, be-
cause it may cause faint recording and poor playback.
Clean these parts with a soft cotton swab soaked in
alcohol.
CLEAN ING
TROUBLE CHART
SYMPTOM CAUSE REMEDY
Motordoes notrun, and pilot
light does not light. AC cord disconnected.
Fuse blown.
Connect AC cord.
Replace fuse.
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2.
Distorted recordings and
poor erase. I. Bias oscillator tube defec-
tive. l. Replace bias oscillator tube.
Pilot light lights, motor runs,
but no record or play. t. Speaker wires disconnected
or broken. l. Connect or replace speaker wires.
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Speaker hum at fuII volume. I. Head cable disconnected. t. Reconnect head cable.
Page 5

TROU BLE CHART (CON'T" )
SYMPTOM CAUSE REMEDY
Motorruns. pilotlightlights, I. Defective rectifier tube. I. Replace rectifier tube.
no record or playback, no
; speaker hum, and VU meter 2. Defective output tube. 2. Replace output tribe.
does not read on record.
No record or playfack, but l. Preamplifier tube defective. I. Replace preamplifier tube.
slight speaker hum variable
with volume control.
Noisy playbackor poorhigh- I. Heads misaligned. I. See "Head Alignment. "
frequency response. 2, Heads magnetized. 2. Dernagnetize heads.
Wow or flutter at? L/2-ips 1. Speed change bushing slip- l. Tighten screw (120).
speed. ping on shaft.
lnsufficientdrive at? L/ 2-or I. Defective main drive idler l. Replace main drive idler
3 3/4-ips speeds. wheel (3i). wheel (3I).
2. Oil on capstan. 2. See "Cleaning. "
3. Main drive belt ([8) defec- 3. Replace main drive beft (IlB).
tive.
4. Drive motor(I24)or starting 4. Replace drive motor (I24) or
capacitor defective. starting capacitor.
Tape spills when going f rom I. Reel diameters unequal. l. Tape reels mustbave the same
wind or rewind to stop. diameter.
2. Brake shoes (34) and (80) 2. Replace oradjust brake shoes
worn or out of adjustment. (3a) and (80).
lndex Counter does not I. Counter belt (I27) worn or l. Replace counter belt (127).
function. broken.
MECHANICAL PARTS LIST
Ref .
No- Part No. Description
I
2
3
4
5
6
7
I
9
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t2
l3
t4
l5
r6
l?
t8
l9
20
20A
2T
90-50-43
90-50-r5
90-50-47
90-50-64
90-52-27
90-50-16
90-38
90-50-22
90-50-r?
90-50-30
90-50-89
90-50-79
90-50-81
90-50-80
90-52-23
90-52-r2
90-50-94
90-50-32
Reel Table Screw(2)
Reel Table (2)
Pinch Wheel Screw
Pinch Wheel-Models 90 & 90-S
Pinch Wheel-Model 90-C
Transport Deck Panel
Record-Play Knob
Set Screw
Wind-Rewind Knob
Transport Deck Panel, Head &
Controls
Take-up Spring Post Brackel
Bracket
Wind-Take-up Slide Bar Spring-
Models 90 & 90-S
Bracket
Retaining Ring
Take-up Brake Link Lever
Take-up Brake Spring
Take*up Brake Bar Lever
Pause Lever-Model 90-C
Pause- Lever Load Spring-Model
90-c
Wind-Rewind Operating Cam
Set Screw
Steel Ball.
Ref.
No. Part No. Description
22
23
24
25
26
27
28
29
30
3t
32
33
34
35
36
3?
38
39
40
90-50-86
90-50-90
90-50-?8
90-50-8?
90-50-25
90-50-24
90-50-36
90-50-?2
90-50-92
90-50-82
90 -50-7?
90-50-5r
90-50-39
90-50-91
90-52-43
90-50-93
Rewind-Take-up Control Pivot
Roller
Take-up Brake Link Spring
Main-Brake Pivot Bar Lever
Wind-Take-up Control Pivot
Lever-Models 90 & 90-S
Deck Baseplate (State Model)
Take-up Spindle
Splined Roller
Retaining Ring
Washer
Main-Drive Idler Wheel
Drive Idler Load Spring
Wind-Take-up ldler Pivot Bar
Lever
Brake Shoe, Small
Main-Drive Idler Pivot Lever
Screw
Spindle Mounting Plate
Roller Securing Screw
Drive Idler Pivot Lever-
Models 90 & 90-S
Drive Idler Pivot Lever-
Model 90-C
Roller
Plav-Record Operating Cam
Page 6

4l
42
43
44
irs
46
47
4B
49
50
5I
52
53
54
60
6l
62
63
64
65
66
6?
6?A
6B
69
?0
?i
72
?3
74
?5
?6
17
?8
?9
80
8i
82
B3
84.
85
86
-1
MECHAN ICAL PARTS LIST (CON'T. )
90-52-21
90-52-08
90-51-??
90-5r-06
90-50-5?
90 -52-04
90 -52-0?
90-52-26
90 -52-tI
90-50-48
90-5r-96
90-5r-?3
90-51-18
90-50-55
90-31
90-5r-64
90-51-?2
90 -5I-95
90-52-05
90-52-13
90-52-r0
90-50-44
90-50-45
90-50-63
90-52-46
90-50-02
90-52-06
90-52-42
90-50-36
90 -50-39
90-50-65
90-50-?7
90-50-?5
90-50-76
90-50-0?
90-50-39
90-50-33
Ch. 2 Shorting Switch
Rewind Activating Lever
Record Lock Button
Record Lock Spring
Record Lock Screw
Lockwasher
Insulator
Insulator
Rewind Idler Wheel
Rewind Positioning Lever
Tape-Drive Idler Load Spring
Rewind Intermediary-Idler Load
Spring
Head Cover Screw
Head Cover-Model 90-C
Head Cover-Model 90-S
Head Cover-Model 90
Head Screw
Michigan Mag. Head Ass'y.,
Stereo-Model 90-S
Head Ass'y. , Monaural-Model 90
Head Ass' y., Stereo-Model 90-S
Multierase Head Ass'y. ,Stereo-
Model 90-C
Retaining Ring
Washer
Rewind Intermediary-Idler Whee
Model 90-C
Intermediary-Idler Spring Lever
Screw
Intermediary-Idler Spring Lever
Rewind-Idler Release Spring
Tape -Guide BalI-Bearing Screw
Tape-Guide Top Plate
Tape-Guide !trasher
Tape-Guide BaII Bearing
Feed-Reel Spindle Ass'y. -Model
90-C Includes Items 6? thru 72
Feed-Reel Spindle Ass'y. Belt
Rewind-Models 90 & 90-S
Rubber Rewind Drive Ring-
Model 90-C
Conical Spindle Spring
Washer
Retaining Ring
Splined Roller
Washer
Spindle Housing Screw
Spindle Mounting Plate
Take-up Spindle Spring
Washer
Retaining Ring
Brake-Shoe Mounting Screw
Brake Shoe, Large (State Size)
Feed-Reel Brake Bar Lever
Brake-Shoe Nut
Feed-Reel Brake-Spring
Index-Counter Ass'y.
Spindle Mounting Plate
Control Ass'y. Bracket
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Ref .
No. Part
No, Description
8?
88
89
90
91
92
93
94
95
96
9?
98
99
r00
I0l
r02
I03
r04
r05
r06
IO?
r08
109
ll0
lu
ll2
u3
II4
u5
lr6
li?
ll8
rr9
120
r2l
122
i23
t24
125
r26
r27 *
12B
129
130
90-50-66
90-50-38
90-50-53
90-50-9?
90-50-98
90-50-09
90-50-96
905r-03
90-5r-32
90 -5I-38
90-50-99
90-51-?5
90-51-?6
90-50-95
90 -52 -53
90-51-04
90-52-03
90-50-34
90-50-46
90-52-42
90-50-21
90-52-44
90-51-94
90-50-14
90 -50-6?
90-50-68*
90-50-69
Wind-Rewind Detent
Fiber Washer
Cam
Load Spring
Idler-Lift Operating Cam
Set Screw
Wind-Rewind Control Shaft
Bottom Plate-Control Ass'y.
Bracket
Lockwasher
Screw
Take-Up Spindle Spring
Retaining Cup
Flat Washer
Retaining Ring
Idler Lifting-Levet Load Spring
Switch Shaft
Screw
Hex Nut
Idler Lifting Lever
Amplifier Switch- Bar Control
Cam
Set Sr:rew
FIat $'asher
Cotter Pin
Amplifier-Switch Bar Screw
Amplifier -Switch Slide-Bar
Load Spring
Amplifier-Switch Operating- Bar
Lever
Fiber Washer
Retaining Ring
Rubber Motor Mount
Motor Grounding Spring
Flywheel and Capstah-Models
90 and 90-S
Flywheel and Capstan-Model 90-C
Main Drivd Belt-Models 90 & 90-l
Main Drive Belt-Model 90-C
Motor-Mount Plate Bracket
Speed-Change Bushing Thumb-
screw-Models 90 & 90-S
Speed-Change Bushing Thumb-
screw-Model 90-C
Speed-Change Bushing-Models
90 and 90-S
Speed-Change Bushing-Model
90-c
Upper Knurled Bushing-Models
90-S and 90-C
Motor Mounting Screw
Drive Motor
Set Screw
Counter Pulley
Counter Beit *
Set Screw
Spindle Index-Counter Pulley
Cotter Pin
* Counter ReIt Welsco Prrt
l4l0-54
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9O-C AMP. CHASSIS TOP VIEW.
9O.C AMP. CHASS IS BOTTOM V IEW.
Page l0