Wollensak T-1500 User manual

[1]
Wollensak Model T-1500 Tape Recorder Service Manual
By Matthew S. Taylor. Last modified 5
January 2010.
Certain parts taken from:
Howard W. Sams & Co., Inc.
―Wollensak Models T-1500, T-1515-4,
T-1700, TS-1520.‖ Photofact® Set
564, Folder 15. Indianapolis 6,
Indiana: Jan. 1962.
---. ―Wollensak Model T-1500.‖
Photofact® Set 400, Folder 13.
Indianapolis, Indiana: May 1958.
Introduction
This manual is for the Wollensak T-
1500 tape recorder, which is designed
for operation on 120 VAC, 60Hz.
Models TS-1520 and T-1700 are
similar, differing only in the ability to
operate on different supply voltages. The TS-1520 model has an autotransformer which
allows it to operate on 220VAC, 60 Hz as well as 120VAC. The T-1700 model has a
vibrator inverter which allows it operate off of 12.6 VDC as well as 120 VAC.
The tape record is a complete self-contained recording and playback unit, with a self-
contained speaker. The audio output is also made available at the Preamp. Jack,
allowing it to be fed into an existing home music system, or an external speaker may be
connected to the External Speaker Jack.
Versions of the T-1500
I have found there seems to be an ―early‖ and a ―late‖ version of the T-1500 chassis,
which differ slightly in their electronics. The ―early‖ chassis was made between
approximately 1958 and 1961, and the ―later‖ from 1962 onward. The date of
manufacture is stamped on the underside of the electronics chassis.
Although the main text of this manual refers to the later chassis, notes for the 1958
version may be found in the Appendix on page 32. In the text, sections that differ for
the two versions I mark with a ―§‖, so be sure to check the Appendix for them if you have
the 1958 chassis!

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Table of Contents
Wollensak Model T-1500 Tape Recorder Service Manual ................................................. 1
Introduction ........................................................................................................................ 1
Versions of the T-1500 ........................................................................................................ 1
Specifications....................................................................................................................... 6
Frequency Response........................................................................................................6
Wow & Flutter.................................................................................................................. 6
Signal-to-Noise Ratio ......................................................................................................6
Tape Speeds ..................................................................................................................... 6
Tape Required..................................................................................................................6
Playing Time .................................................................................................................... 6
Power Requirements .......................................................................................................6
Power Consumption ........................................................................................................6
Size ...................................................................................................................................6
Weight..............................................................................................................................6
Function of Controls, Indicators, and Switches ................................................................. 7
Power Switch ................................................................................................................... 7
Tone Control .................................................................................................................... 7
Volume Control................................................................................................................ 7
Function Keys .................................................................................................................. 7
Stop .............................................................................................................................. 7
Record .......................................................................................................................... 7
Play............................................................................................................................... 7
High-Speed Lever ............................................................................................................ 7
Instant Stop & Record Lock Lever ..................................................................................8
Record Level Indicator ....................................................................................................8
Record Mike/P.A.–Monitor Switch ................................................................................8
Speed Selector..................................................................................................................8
Index Counter ..................................................................................................................8
Purpose of Jacks on Rear ....................................................................................................8
Input Jack ........................................................................................................................8
External Speaker Jack ..................................................................................................... 9
Preamp Output Jack........................................................................................................9

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Operating Instructions ........................................................................................................ 9
Preparation ......................................................................................................................9
Recording with a Microphone ......................................................................................... 9
Monitoring ...................................................................................................................9
Recording from an External Source.............................................................................. 10
Tape Erasure.................................................................................................................. 10
Playback ......................................................................................................................... 10
Playback with External Amplifier.............................................................................. 10
Splicing & Editing .......................................................................................................... 10
Use as a Public Address System .....................................................................................11
Disassembly Instructions.................................................................................................. 15
To Remove Mechanism from Case................................................................................ 15
To Remove Amplifier from Transport Mechanism....................................................... 15
To Remove Amplifier Without Complete Disassembly ................................................ 15
Replacing Sound Head .................................................................................................. 16
Preliminary Tests .............................................................................................................. 16
Function Switch Explanation.............................................................................................17
Electrical Adjustments ...................................................................................................... 18
Head Azimuth................................................................................................................ 18
High Frequency Equalization Adjustment §................................................................. 19
Hum Balancing Adjustment.......................................................................................... 19
Bias Current Adjustment §............................................................................................ 19
Cleaning.............................................................................................................................20
Lubrication ........................................................................................................................20
Troubleshooting Mechanical Problems ............................................................................20
No Tape Drive in Play or Record...................................................................................20
Take-up Reel Does Not Turn Although Tape Feeds Past the Capstan ......................... 21
Take-up Reel Stalls in Playback or Record when Reel is Nearly Full........................... 21
No Fast Forward But Capstan Turns ............................................................................ 21
Fast Forward Stalls with Full Reel ................................................................................ 21
No Rewind But Capstan Turns...................................................................................... 21
Tape Overruns or Spills When Functions Are Changed ............................................... 21
Speed Irregularities (―Wow‖ & ―Flutter‖) ..................................................................... 21
Bottom Motor Shaft Pin Rubs Bottom Ventilating Grill...............................................22

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Insufficient Tape Take-up .............................................................................................22
Tape Squeal or Squeak ..................................................................................................22
Troubleshooting Electrical Problems ............................................................................... 22
Weak Playback Volume or No High Frequencies .........................................................22
Recorder Dead, Pilot Light Off ...................................................................................... 23
No Playback or Record ..................................................................................................23
Plays, But Does Not Record Or Records But Does Not Playback .................................23
Weak or Distorted Record, Playback of Prerecorded Tape Normal .............................23
Record Level Indicator Inoperative or Operation Defective ........................................24
Hum in Record or Playback...........................................................................................24
Weak or No Erase, Records Over Previous Recordings................................................24
Microphonic Noises.......................................................................................................24
No Sound, Neon Lamp Flashes with Signal..................................................................24
Excessive Tape Hiss....................................................................................................... 25
Electrical Components ...................................................................................................... 25
Tubes & Lights §............................................................................................................. 25
Capacitors §.................................................................................................................... 25
Resistors §......................................................................................................................26
Inductors & Transformers §.......................................................................................... 27
Speaker .......................................................................................................................... 27
Rectifiers ........................................................................................................................ 27
Fuse................................................................................................................................ 27
Switches §.......................................................................................................................28
Motors............................................................................................................................28
Mechanical Parts List ........................................................................................................28
Appendix: Early Version Procedures & Components......................................................32
High Frequency Equalization Adjustment (p. 20)........................................................ 32
Bias Current Adjustment (p. 20)................................................................................... 32
Electrical Components .................................................................................................. 32
Tubes & Lights (p. 26) ............................................................................................... 32
Capacitors (p. 26).......................................................................................................32
Resistors (p. 27) .........................................................................................................32
Inductors & Transformers (p. 28) ............................................................................. 32
Switches (p. 29).......................................................................................................... 33

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Specifications
Frequency Response
3¾ ips: 40–8,000 Hz ± 3 dB
7½ ips: 40–15,000 Hz ± 3 dB
Wow & Flutter
Less than 0.3% for both speeds.
Signal-to-Noise Ratio
Greater than 48 dB.
Tape Speeds
3¾ and 7½ inches per second.
Tape Required
Up to 7-inch reel, ―A‖ wound tape (shiny side out).
Playing Time
A 7-inch reel of 1-mil tape recorded on both tracks at 3¾ ips will play for 3 hours; other
tape lengths, thicknesses, and speeds are proportional.
Power Requirements
Model T-1500: 120 VAC, 60Hz.
Model T-1520: 120 VAC or 220 VAC, 60 Hz.
Model T-1700: 120 VAC, 60 Hz or 12.6 VDC.
Power Consumption
100 Watts
Size
Approximately 6½ inches by 10¼ inches by 11¾ inches.
Weight
T-1500: 20 pounds
T-1520: 22 pounds
T-1700: 26 pounds

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Function of Controls, Indicators, and Switches
Power Switch
Rotating the tone control a few degrees clockwise turns the tape recorder on,
applying power to both the amplifier and transport motor. Thus the motor is ready to
transport the tape immediately whenever the Play or Record keys are pressed or the
High Speed Lever actuated. When the tone control is turned to the ―Off‖ position, a tab
on the knob trips the transport mechanism, locking it in the ―Stop‖ position for storage.
Tone Control
Turning the knob further varies the tone. The ―Balanced Tone‖ setting emphasizes
very high and very low frequencies, the degree of emphasis varying with the volume
control setting, thus producing a response which closely matches the normal hearing
response of the human ear. The ―Bass‖ setting cuts high frequencies and emphasizes
low ones. The ―Treble‖ setting emphasizes high frequencies. The ―Hi-Fi‖ position
produces a response suitable for use with external amplifiers.
The tone control has no effect when recording.
Volume Control
This regulates the volume during both recording and playback, as well as adjusting
the signal level applied to the Preamp Output jack.
Function Keys
Stop
Cancels either playback or recording. Brakes are applied to the spindles, the tape is held
away from the head, and the function switch is put into the ―Stop‖ position.
Record
Before the record key can be pressed to begin recording, the record lock lever must be
pulled. This releases the brakes, holds the tape against the head using pressure pads,
pushes the pressure roller against the capstan (which moves the tape), and turns the
function switch to ―Record.‖
Play
Pressing the play key results in the same action as record, except the function switch is
put into the ―Play‖ position.
High-Speed Lever
Moving this lever to the right causes the tape to advance at a much higher speed than
that used during recording or playback. When this lever is moved to the left, tape is
rewound onto the supply reel. The high-speed lever can be moved when the recorder is

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in any function (Play, Record, or Stop) and the play or record keys will be automatically
released. When the lever is returned to neutral, the recorder is left in the ―Stop‖ mode.
Instant Stop & Record Lock Lever
The record lock lever is provided as a safety feature to prevent accidental erasure of
prerecorded tapes. It must be pulled towards the front of the recorder and held there
before ―Record‖ mode can be entered.
It also serves as an instant stop lever when the tape is in motion during record or
playback. Pulling the instant stop lever disengages the tape drive and instantly stops the
tape. The recorder returns to its previous operation when this lever is released.
Record Level Indicator
During recording, the left or ―Normal‖ half of the indicator flashes to indicate a
correct volume setting. The right or ―Distorted‖ half flashes if the volume setting is too
high. To present the volume level for recording before the record key is pressed, the
tone control should be turned to ―Treble.‖ However, after the record key is pressed, the
tone control adjustment has no effect. When playing prerecorded tapes, ignore the
flashing of this indicator.
Record Mike/P.A.–Monitor Switch
This is a slide switch mounted on the rear of the tape recorder. When the switch is in
the ―Record Mike‖ position, the speaker does not operate in both record and stop
modes. This is also true of any speaker which may be connected to the speaker output
jack at the time. When this switch is in the ―P.A.–Monitor‖ position, the speaker is
connected so that the recorder can be used as a public-address system, or so that
program material may be monitored as it is being recorded. This switch has no effect in
playback mode.
Speed Selector
The speed selector is mounted near the index counter at the left front of the tape
recorder, and sets the speed of the tape. The speed selected appears on the speed
selector dial in inches per second. The recorder does not need to be stopped to change
speeds. Rapid forward winding can be further accelerated by selecting 7½ ips.
Index Counter
The index counter can be set to zero by turning the knurled knob towards the rear of
the tape recorder. If the counter is zeroed when recording or playback starts, tape
selections may be indexed, thus providing quick and accurate replay or editing.
Purpose of Jacks on Rear
Input Jack
The input jack can be used to connect a microphone or external audio source to the
tape recorder. The proper input circuit is automatically selected by means of different

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plug lengths for each application. A short (1-inch) plug is used with the microphone and
a longer (1
316
-inch) plug is used for external audio sources (televisions, radios, &c.).
External Speaker Jack
An external speaker can be connected to the tape recorder through this jack. The
impedance of the speaker should be 6-8Ω. Accessories such as the TE-401 earphone or
headphones may also be used. The internal speaker is disconnected when a plug is
inserted into this jack.
Preamp Output Jack
The preamp output jack is provided for connection to an external audio amplifier,
bypassing the internal output stage and speaker. The output impedance is
approximately 33 ĸΩ.
Operating Instructions
Preparation
1. Connect the tape recorder to the proper power source using the cord provided.
2. Make sure the high-speed lever is in the center or neutral position.
3. Turn the recorder on by rotating the tone control a few degrees clockwise.
4. Threading the Tape
a. Press the stop key.
b. Place a full reel of tape (glossy side out, i.e. ―A‖ wind) on the left spindle.
c. Pull a length of tape off the supply reel and lower it into the threading slot.
d. Attach the end of the tape to the empty take-up reel.
e. Set the index counter to zero.
Recording with a Microphone
1. Insert the microphone plug into the input jack on the rear of the recorder.
2. Set the slide switch to ―Record Mike.‖
3. Select the desired tape speed.
4. If you wish to preset the record level, then:
a) Turn the tone control to ―Treble.‖
b) Adjust the volume control until the ―Normal‖ half of the indicator flashes.
c) No flashing should occur on the ―Distorted‖ half.
5. Pull back the Instant-Stop-Record Lock Lever and press the record key.
6. Release the Instant Stop Lever.
7. Recording will start.
8. To stop recording, press the stop key.
9. To rewind the tape, move the high-speed lever to the left.
Monitoring
The signal can be monitored during recording if the slide switch on the rear panel is set
to ―P.A.–Monitor.‖ However, care must be taken to keep the microphone away from the

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speaker, otherwise acoustic feedback may cause squealing. This hazard can be avoided
if earphones are used instead of the internal speaker. The earphones should be plugged
into the external speaker jack.
Also, before rewinding the tape, additional material may be recorded by turning over the
full take-up reel and placing it on the supply spindle.
Recording from an External Source
1. Connect the signal source to the input jack using an A196-13 Hi-Fi cable, or similar
cable with a long plug.
2. Proceed with steps 2 to 9 for ―Microphone Recording‖ given above.
Recordings can be made from external sources such as phonographs, radios,
televisions, or AM-FM tuners. If the external source has a level control for its output
jack being used, it should be set so that the tape recorder’s volume control setting will be
somewhere near its midrange for proper operation of the level indicator. Tone controls
and loudness controls on the external source should be set to a flat setting.
Tape Erasure
Whenever a recording is made, any previously-recorded material on the tape is
automatically erased before the new material is recorded. Erasing is performed only
when the recorder is set to ―Record.‖ Half of the tape is erased at a time. To erase
without recording new sound, turn the volume control down completely before entering
―Record‖ mode.
Playback
1. Thread the tape as described under Preparation Step 4, a-e.
2. Locate the desired starting point using the High Speed Lever.
3. Set the speed selector to the speed used when the material was recorded.
4. Push down the play key.
5. Adjust volume and tone as desired.
6. For dual-track recordings, do the following:
a) Turn over the tape at the end of the first track.
b) Put it on the supply on the supply spindle.
c) Rethread the tape and play as before.
Playback with External Amplifier
1. Connect the external amplifier to the preamp output jack on the back of the recorder
using a shielded cable such as Wollensak A196-13 Hi-Fi cable.
2. Set the recorder’s tone control to ―Hi-Fi.‖
3. Adjust the recorder’s volume until the ―Normal‖ side of the level indicator flashes.
4. Adjust the amplifier’s volume and tone controls as desired.
Splicing & Editing
Tape from a dual-track tape recorder may be edited only if one track has been
recorded or if the program on the other track is not wanted. Undesirable portions can
be cut out, announcements can be inserted between selections, and so on. Unused

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sections of tape can be spliced together and reused. Tape should be cut on a diagonal
and the ends joined together with splicing tape on the glossy side. Any excess width
should be trimmed.
Program material can be edited very precisely in the following manner:
1. Press ―Play‖ key and stop the tape with the instant stop lever.
2. Turn the reels by hand to locate the word or sound.
3. Remove the head cover and mark the tape at the right-hand element in the black slot
of the sound head.
4. Remove the tape from the threading slot and cut on the mark.
Use as a Public Address System
1. Press the stop key of the recorder.
2. Set the slide switch to ―P.A.–Monitor.‖
3. Plug the microphone into the input jack.
4. Plug an external speaker or speakers into the external speaker jack.
5. Keep microphone and speaker(s) separated as far as possible to avoid feedback.
Figure 1: Top View of Transport Mechanism

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Figure 3: Transport Mechanism with Top Mechanism Plate Removed
Figure 2: Top Plate Mechanism

[13]
Figure 4: Exploded View of Transport Mechanism

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Figure 5: Exploded View of Top Mechanism Plate

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Disassembly Instructions
To Remove Mechanism from Case
1. Remove top panel.
a) Remove five (5) painted screws holding top panel (three screws between reel
spindles and one on each forward corner).
b) Remove two chrome-plated screws on top of perforated grill directly in front of
head cover.
c) Remove clean-out cover bar by pulling upward.
d) Carefully pry up the top panel at the rear enough to just clear the reel spindles.
e) Pull back the panel to remove.
2. Remove bottom cover by removing the following:
a) Four (4) screws in line with and inside rubber feet
b) Two (2) screws on side panels a half-inch above rear feet. (For Model T-1700,
one screw on left side-panel, the other inside right rear foot.)
c) Two (2) screws one-inch to the side of the top cover hinges.
d) Lastly the bottom cover.
3. Remove counter belt from counter pulley.
4. Remove high-speed knob by pulling up.
5. Remove the three remaining Philips head screws from each side panel.
6. Remove side panels.
7. For Models TS-1520 and T-1700, remove the additional power plug to remove the
left-side casting.
To Remove Amplifier from Transport Mechanism
1. Unplug motor plug.
2. Unplug head plug.
3. Remove nylon function switch arm from bottom of amplifier by pulling off.
4. Remove four Philips head screws (3 long, 1 short) from bottom of amplifier chassis
holding each corner.
5. Lift amplifier chassis away from tape transport mechanism.
To Remove Amplifier Without Complete Disassembly
1. Turn Speed Selector to 7½ ips.
2. Remove bottom cover and right side panel as outlined above in ―To Remove
Mechanism from Case‖ steps 2, 5, and 6.
3. Pull the nylon function switch arm out of the chassis bottom.
4. Unplug the head plug, motor plug, and speaker plug.
5. For Models TS-1520 and T-1700, remove the additional power plug.
6. Remove the four Philips head screws holding the chassis corners to the mechanism.
7. Note the position of the plastic insulator between chassis and mechanism.
8. Lift chassis up and to the right to remove.
9. When reassembling, make sure mechanism is in the 7½ ips position and the nylon
chassis insulator is in place!

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Replacing Sound Head
1. Remove head retainer spring (137).
2. Lift head and brass alignment plate from head shield cup.
3. Unplug head cable plug.
4. Pry head from brass alignment plate, noting position of location pins.
5. Place the new head over the pins in the aligning plate in the proper location and
press into place.
6. Replace alignment plate into head cup, making sure the two brass pivot studs
engage the two holes in the plate.
7. Replace head retainer spring.
8. Align head azimuth as described on page 18.
Preliminary Tests
Failure to pass any of these tests indicates a fault that should be remedied!
1. Cleaning
a) Remove head cover casting (3) and pull out clean-out cover casting (4).
b) Clean heads, tape guides, and capstan with isopropyl alcohol.
2. Setup
a) Press stop key.
b) Place high-speed knob in the middle or neutral position.
c) Turn on recorder by rotating tone control.
3. Testing Brakes
a) Place reel of tape on rewind (left) spindle.
b) Pull out about 12 inches of tape.
c) Brakes should be engaged.
d) Pull required on reel should not distort the tape, but there should be sufficient
drag to prevent spilling of tape.
e) Drop tape in threading slot, and attach free end to take-up reel (right).
f) Reel should rotate freely counterclockwise and drag when rotated clockwise.
4. Playback Mechanism Test
a) Press play key; it should latch down.
b) Brakes on both spindles should release.
c) Record pressure pad assembly (142) and erase pressure pad assembly (143)
should press tape squarely against head.
d) Pressure roller (103) should push tape against flywheel-capstan assembly (47)
causing tape to move smoothly past the head as it passes flyback-capstan
assembly (47).
e) The counter should tally each revolution of the supply reel.
5. High-Speed Test
a) Move high-speed knob to the right.
b) Play key should release.
c) Pressure roller and pressure pads should release.
d) The tape should move forward at greatly increased velocity.
6. Pressure Pads & Braking
a) Return high-speed knob to the middle or neutral position.
b) Pressure pads and pressure roller should remain disengaged.

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c) Brake pressure on spindles should increase smoothly, bringing tape to a stop
without spilling.
7. Recording System Test
a) Make a recording with the microphone.
b) Adjust volume control while speaking so that normal indicator flashes and
distorted does not.
8. Rewind Test
a) Move high-speed knob to the left.
b) Record key should release and the tape should rewind quickly.
9. Playback Test
a) Playback recording.
b) Check volume, tone, and overall quality.
c) Pull instant stop arm (104) forward.
d) Tape should stop at once.
e) When arm is released, tape should start instantly without spilling off reels.
10. Erasure Test
a) Rewind tape and rerecord over previous recording.
b) All trace of previous recording should be erased on the portion of tape reused.
c) Check for irregularities in playing speed (―wow‖ and ―flutter‖).
Function Switch Explanation
The function switch is a ―slide‖ wafer type with three positions (play, stop, and
record). It has 10 copper strips mounted on two sliding phenolic wafers that short
various stationary contacts together. The wafers can hold 36 stationary contacts in total,
but only 31 of these are used on the T-1500, TS-1520, and T-1700 models. Being as both
the strips and the contacts are placed at several different ―levels‖ along each wafer, it is
difficult to see which contacts are shorted together in each of the three positions.
Howard Sams did an atrocious job of illustrating this switch in their schematic, and gave
no written clarification of it.
In my schematics, I show the function switch as ten SP3T and three SPST switches
ganged together. The positions of SP3T switch correspond to the play, stop, and record
modes respectively. The SPST switches are engaged in either play or record as specified.
My pin numbering is the same as Sam’s: with the knob-side of the chassis to the left, the
numbering proceeds left to right, bottom to top. Though electrically and functionally
identical to the actual switch, my depiction makes it much, much easier to follow. By
following my clarified schematic, the action of the function switch is as follows:

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SW
Playback
Stop
Record
S1
Input jack shorted.
Input jack connected
to preamplifier thru
C1.
Input jack connected to
preamplifier.
S2
Tone control active.
Tone control disabled.
S3
Equalization selected.
Equalization disabled.
S4
Erase head and bias-
oscillator coil shorted
(erase disabled).
Erase head and bias-oscillator coil not shorted.
S5
Read/write head ―-― grounded.
R/W head ―-― connected thru
K1to signal to be recorded.
S6
R/W head ―+‖
connected to
preamplifier.
R/W head ―+‖ grounded.
S9
V2B amplifier on.
V2B amplifier off; functions as
diode, mixing amplified audio
from V2A with oscillator signal.
S10
Amplified audio at
output jack.
Preamplifier output jack shorted.
S11-
13
V4configured as pentode amplifier.
V4configured as triode
oscillator.
S15,
16
Speaker connected to
output.
Speaker connected to
output only if ―P.A.‖
selected.
Speaker connected to output
thru R45 only if ―Monitor‖
selected.
Electrical Adjustments
Head Azimuth
It is important the head be lined up so that the record-playback (read/write) head
gap is at a 90° angle with respect to the direction of tape travel. If the head is
misaligned, there will be some loss of the higher frequencies and a lower overall output.
An alignment tape, which used to be available from Ampex® or the larger radio
supply houses*, should be used to align the head. The tape should have a full-track
recording at a frequency higher than six kilohertz. While the alignment tape is being
played, adjust alignment screw (140) for maximum output. Cement screw with
Locktite®.
If an alignment tape is not available, play a previously-recorded tape and adjust
alignment screw (140) for maximum treble response. Azimuth is the only head
adjustment needed on Models T-1500, TS-1520, and T-1700.
*I do not know where such an alignment tape could be found now—MST.

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High Frequency Equalization Adjustment §
An adjustment is provided in the cathode circuit of V2A (12AT7) to compensate for
high frequency losses which accompany long-term head wear. This equalization has
more effect upon the playback than it has upon the recording process; therefore, the
adjustment is made for best results during playback.
The equalization adjustment has been properly made at the factory and should not
require readjustment for at least 500 hours of use. Before any adjustment is made, the
heads should be carefully cleaned with isopropyl alcohol. Make the adjustment in the
following manner:
1. Record signals of equal amplitude at 10 kHz and 15 kHz, well below (-15 dB)
normal level.
2. Set the tone control for ―Hi-Fi.‖
3. Measure the two signals at the Pre-amp output jack during playback using an
oscilloscope.
4. With a plastic adjustment tool, adjust the core of the peaking coil (L3) so that
the output at 15 kHz is the same as at 10 kHz, using the 10 kHz signal as a
reference. The threaded shaft of the core is accessible from the tube side of
the chassis, near hum control R29 between transformers T1and T3.
Hum Balancing Adjustment
Two access holes are provided in the bottom cover (near manufacturer’s label) for
adjustment of hum controls R29 and R31. The access hole nearest the manufacturer’s
label provides for the adjustment of R29, and the other for R31. Adjust them using a
small bladed screwdriver.
Adjust hum controls R29 and R31 as follows:
1. Turn tape recorder on and allow tubes to warm up.
2. Press play key. Do not use a tape.
3. Turn volume control to ―0‖ position (minimum).
4. Adjust R29 for minimum hum.
5. Turn volume control to the ―10‖ position (maximum) and adjust R31 for
minimum hum. If R31 adjusts for minimum hum at one end of its rotation,
leave volume control at maximum and readjust R29 for minimum hum.
Bias Current Adjustment §
1. Remove bottom cover of tape recorder (see ―To Remove Mechanism from Case‖
on page 15).
2. Unplug 4-prong head plug M11.
3. Remove a half-inch of insulation from a length of hook-up wire.
4. Wrap several turns of the bare wire around pin #2 of the head plug.
5. Reinsert plug into socket, being careful not to short the wire to the chassis or
another pin on the plug.
6. Connect a VTVM or DMM†set to read AC RMS volts between the wire (pin #2)
and chassis ground.
7. Operate the recorder in ―Record‖ mode.
†Capable of accurately measuring a 75 kHz signal.

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8. With a plastic (not metal) flat-bladed adjustment tool, adjust bias/erase
oscillator coil T4for a voltage of 50 VAC.
Cleaning
The majority of defects, other than wear or breakage, can be traced to dirty surfaces.
The play-record and erase heads, capstan, and pressure roller are subject to an
accumulation to tape coating residue, which is worn off the tape as it passes these parts.
This accumulation should be periodically removed since it will cause faint recording and
poor playback. Wipe off the above surfaces carefully using a clean cloth dampened
slightly with isopropyl alcohol.
Lubrication
All moving parts in this recorder were permanently lubricated at time of
manufacture. Under normal use, further lubrication should not be required. In heavy-
duty service, the following parts should be lubricated once a year with a drop of light
lubricating oil:
The top and bottom motor bearings.
The top and bottom flywheel (47) bearings.
Pressure roller (103) bearing.
All idler and drive wheel bearings.
The reel spindle bearings.
The basic rule is—do not over lubricate! Oil must be kept off all rubber idlers, belts,
the periphery of the flywheel, and any parts that might transfer oil to them. Always wipe
excess lubricant from parts that have been lubricated.
Troubleshooting Mechanical Problems
No Tape Drive in Play or Record
Possible Causes
Solution
Tape wound around capstan.
Free stuck tape.
Pressure roller tension spring (89) broken or
disconnected so that pressure roller (103) is not
held against capstan.
Connect or replace the spring.
Instant-stop brake spring (91) broken or
disconnected. Brakes will not release and the
pull of the capstan may be sufficient to break
the tape.
Connect or replace the spring.
Idler drive spring (122) broken or disconnected.
Left high-speed idler assembly (120) is not held
against motor pulley (55) and flywheel (47).
Connect or replace the spring.
Slow speed idler spring (60) broken or
disconnected and the slow speed idler assembly
is not held against motor pulley (55) and
flywheel (47).
Connect or replace the spring.
Motor pulley (55) loose on its shaft.
Tighten motor pulley set screw.