Wollensak T 1500

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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 3

16 -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

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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 K1 to 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 V4 configured as pentode amplifier. V4 configured 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 T1 and 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 T4 for 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.


Idler drive spring (122) broken or disconnected. Left high-speed idler assembly (120) is not held against motor pulley (55) and flywheel (47).


Slow speed idler spring (60) broken or disconnected and the slow speed idler assembly is not held against motor pulley (55) and flywheel (47).


Motor pulley (55) loose on its shaft. Tighten motor pulley set screw.

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Grease or oil on high (120) or low speed (58) idler tires.

Wipe lubricant off tires.

Sticking idler slide (59 or 119)

Take-up Reel Does Not Turn Although Tape Feeds Past the Capstan

Take-up belt (45) broken or off pulley (43). Replace belt or place it back on pulley.

Take-up Reel Stalls in Playback or Record when Reel is Nearly Full

Grease or oil on take-up belt (45) or on take-up clutch felt (41).

Clean with alcohol. Replace felt if necessary.

No Fast Forward But Capstan Turns

High-speed idler spring (115) broken or disconnected. Idler assembly (120) not held against flywheel or spindle cup (13).

Connect or replace spring.

Fast Forward Stalls with Full Reel

Grease or oil on idler assembly tire. Wipe lubricant off tire.

No Rewind But Capstan Turns

Rewind spring (32) broken or disconnected. Rewind spindle and tire assembly not held against motor pulley (55)


Tape Overruns or Spills When Functions Are Changed

Brake arm spring (17) broken or disconnected. Connect or replace spring.

Brake roller leaf spring (21) broken or disconnected.


Speed Irregularities (“Wow” & “Flutter”) In general, anything that causes a drag or slipping action other than that occurring

during normal operation can cause wow or flutter. Check for binding in the following:

Flywheel Bearings: Check by moving right and left idler wheels (120) away from the flywheel and rotate the capstan by hand. A slight drag is normally obtained from take-up belt (45).

All Idler and Drive Wheel Bearings

Right and Left Reel Spindles: The brakes should be disengaged or held away before the spindles are turned.

Motor bearings. Check by turning shaft by hand. Check to see that:

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Supply reel is free to rotate and is not scraping against the top plate.

Brakes are completely released.

Pressure roller (103) is making good contact with capstan. Pressure roller tension spring (89) should not be too weak or too strong.

Capstan and pressure roller are clean. Check for irregularities in the following:

Idler wheel surfaces

Pressure roller (103) surface

Take-up Tension: The take-up clutch is designed to slip during normal operation to compensate for the different rate of rotation of a full and an empty reel. Check by holding the right-hand spindle while the recorder is in Play mode. The clutch action should be smooth and non-pulsating. If the surface of the take-up clutch (41) is gummy or if the felt is worn, it should be replaced.

Bottom Motor Shaft Pin Rubs Bottom Ventilating Grill Fix by placing washers under motor supports on side rubbing to more-nearly center the motor in grill opening when recorder is in normal position.

Insufficient Tape Take-up

Clutch felt (41) may be worn. Replace felt if needed.

Take-up action may be increased by adding another washer (46) under take-up pulley assembly.

Tape Squeal or Squeak Tape squeal or squeak is heard as a high-pitched warbling sound that accompanies recording or playback. It can be noticed in quiet surroundings when listening close to the sound head with the volume turned down. Squeal or squeak can be minimized as follows:

Clean head, pressure pads, and tape guides with alcohol.

Use a good brand of tape. Inferior tape with insufficient lubrication may be helped by treating with silicon lubricant.

Replace pressure pad felts. Place thin Teflon® film tape over pads if needed.

Slightly decrease the tension of pressure pad springs (144 & 145).

Troubleshooting Electrical Problems

Weak Playback Volume or No High Frequencies 1. Check for faulty silicon diodes (D1 & D2) in voltage doubler power supply. 2. Check for open fuse resistors R22 and R23. 3. Check for low plate voltage to 12AB5 power amplifier tubes. 4. Check for dirty head.

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5. Check pressure pads for weak or improper contact. 6. Wrong type or tape or wind. Dull side of tape should be wound ―in‖ (―A‖ wind). 7. Check head azimuth adjustment. 8. Check head for wear. If head is worn, make compensating adjustment (see ―High

Frequency Equalization Adjustment‖ on page 19) or replace if head wear is too great.

9. Check adjustment and condition of L3. 10. If high-frequency response is lacking only at 3¾ ips, check operation of

equalization switch S8.

Recorder Dead, Pilot Light Off 1. Check fuse F1. If blown, check for B+ shorts, and make sure power source

matches power requirement listed on nameplate. 2. Check power cord and power switch.

No Playback or Record 1. Check tubes and voltages as indicated on schematic diagram. Trouble can be

localized by monitoring output at preamp jack: if signal is present here, trouble must be in some succeeding stage; if no signal is present, trouble may be in preceding stages or in power supply.

2. Check play-record head.

Plays, But Does Not Record Or Records But Does Not Playback 1. Amplifier Function Switch Nylon Arm out of Adjustment

a. See if switch arm moves the function switch all of the way back when play key is pressed or all the way forward when the record key is pressed.

b. The switch arm requires adjustment if pushing the switch arm by hand moves the function switch slide slightly more to the rear or front when the play or record keys respectively are pressed.

c. To adjust, turn the hexagon nylon cam so that its pin moves the function slide switch as far as possible, both backward and forward when the play and record keys are pressed.

d. To check if adjustment is correct, press the stop key; sight straight down the rear edge of the function switch ⅞-in access hole into the amplifier. The rear edge should appear to bisect the small eyelet on the function switch slide.

2. Check for drag or binding on the function switch slide. Switch should not require more than 20 ounces (570 grams) to move back and forth.

3. Check recording source; microphone may be dead, or other source may be faulty. 4. Oscillator tube V4 may be defective; if so, listener may perceive distortion in

playback. 5. Check oscillator coil T4.

Weak or Distorted Record, Playback of Prerecorded Tape Normal 1. Check oscillator tube V4. 2. Check input jack for proper contact.

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3. Check microphone or other input source for quality of signal. 4. Check plugs; microphone plug should be a two-circuit plug with shielded wire

connected to tip and shield connected to body. Shaft of plug should be approximately 1-in long. High level sources require a two-circuit plug approximately 1 3

16 inches long. Failure to push plugs all of the way into jack may

cause distortion. 5. Check record level indicator lamp. A defective lamp may result in a recording

level which is too high or too low.

Record Level Indicator Inoperative or Operation Defective 1. Check for out-of-tolerance resistors. 2. Check for defective NE-45 bulb. 3. Lamp may glow continuously if there is excessive hum or if the amplifier is

oscillating. 4. Distorted indicator should begin to glow when 2V @ 1 kHz appears at preamp

output jack if circuit is working properly.

Hum in Record or Playback 1. Check electrolytic capacitors. 2. Check all stages for heater-to-cathode leakage in tubes. 3. Check hum controls for proper adjustment (see ―Hum Balancing Adjustments‖

on page 19). 4. Hum on a recorded microphone signal may be due to a poorly-grounded shield

on the cable.

Weak or No Erase, Records Over Previous Recordings 1. Check for dirt on erase head. 2. Check pressure pads. 3. Check oscillator coil T4 and oscillator tube V4. 4. Check erase head continuity.

Microphonic Noises Microphonic noises usually develop in the first stages of an amplifier in which the

sensitivity is greatest, but can develop in other stages. Start with the first stage (7025) and try different tubes, selecting the one that is least microphonic.

Dress C12 to clear edges of function switch shield. Dress V1A grid wire (pin #2) to clear C2. Dress C11 to clear input jack shield.

No Sound, Neon Lamp Flashes with Signal 1. Check speaker and speaker contact switch. 2. Check function switch clips for contact. 3. Check connecting cables, jacks, and plugs in output circuit. Make sure speaker

plug is pushed all the way down. 4. Check transformer T2 for open secondary.

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Excessive Tape Hiss 1. Check for sufficient recording level by comparing to a prerecorded tape. 2. Tape may be worn, try a new tape of good quality. 3. Check V4 and associated voltages. 4. Check bias-erase oscillator coil T4 and associated components. 5. Check bias current adjustment (given on page 19). 6. Check the automatic demagnetization circuit which operates by shorting C12 (220

nF) across the play-record coil at the termination of the Record function. This capacitor resonates with the record head to provide a decaying demagnetization transient.

7. Head may be microphonic. If so, replace head.

Electrical Components

Tubes & Lights §

Part # Use Type Description

Lmp1 Panel Lamp 1847 Incandescent

V1 Preamplifier 7025 Low-noise twin triode

V2 AF Amplifier 12AT7 High-µ twin triode

V3 Power Amplifier 12AB5 Beam-power Pentode

V4 Bias Oscillator, Power Amplifier 12AB5 Beam-power Pentode

V5 Record Level Indicator NE-45 Neon Lamp

Capacitors §

Part # Capacitance Voltage Rating

Type

C1, C12 220 nF 100V Polyester

C2, C34 100 nF 400V Film

C3, C29 5 nF 50V Ceramic

C4 22 nF 50V Ceramic

C5, C6, C28 50 nF 50V Ceramic

C7 47 nF 400V Film or Ceramic

C8 1 nF 50V Part of Thick-film Printed Circuit K1

C9 10 nF 50V

C10 1.5 nF 50V C11 100 nF 100V Polyester

C13 680 pF 50V Ceramic

C14 680 pF 50V Part of Thick-film Printed Circuit K2 C15 220 pF 50V

C16, C17 50 nF 400V Film

C18, C19 47 µF 200V Electrolytic

C20, C21, C23, C26

22 µF 350V Electrolytic

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C22 47 nF 250VAC X-Y Metalized Film

C24, C27 33 µF 350V Electrolytic

C30 22 nF 250V

Part of Thick-film Printed Circuit K3

C31 3.3 nF 100V

C32 100 pF 500V

C33 470 pF 1 kV

C35 47 µF 6.3V Electrolytic

C36 100 pF N150 50V Ceramic

C37 100 µF 35V Electrolytic

C38, C41 2 nF ±10% 50V Ceramic or Polyester

C39 220 pF 50V Ceramic


Resistors § All resistors ½W or less carbon-film types unless otherwise noted.

Part # Value Notes

R1 22 MΩ Replace with Digi-Key Part #PPCHHJ22MCT-ND if bad.

R2, R12 10 MΩ

R3, R10, R11

10 kΩ

R4 10 Ω

R5 270 kΩ

R6, R13 220 kΩ 2W metal-film

R7, R39 33 kΩ

R8 200 kΩ with tap @ 20 kΩ

Carbon potentiometer used as tone control, has switch on shaft.

R9 200 kΩ with tap @ 100 kΩ

Carbon potentiometer used as volume control.

R14, R17 200 kΩ

Part of Thick-film Printed Circuit K1 R15 2.2 MΩ

R16 27 kΩ

R18, R36 1 MΩ

R19 22 kΩ

R20 62 kΩ Part of Thick-film Printed Circuit K2

R21 220 kΩ

R22 22 Ω 5W fusible wire-wound

R23, R24 100 Ω 5W wire-wound

R25 1.5 kΩ ½W

R26 1.5 kΩ

R27 22 kΩ

R28 47 kΩ

R29, R31 250 Ω 2W wirewound potentiometers used as hum

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adjust.

R30 2.2 Ω

R32 1.8 kΩ ±5%

R33 100 kΩ

R34, R35 270 kΩ Part of Thick-film Printed Circuit K3

R36 1 MΩ

R37 300 Ω ±5%

R38 680 kΩ

R40 91 kΩ ±5%

R41 180 kΩ ±5%

R42 360 kΩ ±5%

R43 300 Ω ±5% 4W wire-wound

R44 10 kΩ

R45 82 Ω 3W wire-wound

Inductors & Transformers § (The current given for the power transformer is the measured nominal current; a replacement must be rated for at least twice this!)

Part # Name Details

L1 Recording & Playback Head

L2 Erase Head

L3 Equalization Coil

T1 Power Transformer Primary: 120V @ 0.2A Sec. 1: 180V @ 10 mADC) Sec. 2: 12.6V @0.4A Sec. 3: 6.3V @ 1A

T2 Output Transformer Primary Impedance: 1.5 kΩ CT Sec. 1 Impedance: 125Ω CT Sec. 2 Impedance: 8Ω

T3 Driver Transformer Turns Ratio: 6/5 to each secondary

T4 Bias Oscillator Coil

Speaker SPK1 5¼-in. PM 8Ω Loudspeaker

Rectifiers

Part # Original Wollensak # Replacements

D1, D2 A123-5 1N1763 or 1N4004

D3 A123-4 1N4007

Fuse F1 1¼-ampere 125VAC time-delay fuse

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Switches §

Part # Description

S1-S6, S9-S13, S15, S16 Part of Function Slide Switch

S7 Power switch on tone control, SPST

S8 Equalization Switch, SPDT

S14 Mic-Rec/Monitor-P.A. Switch; SPDT

Motors M1 Drive Motor Single-phase hysteresis induction motor

Mechanical Parts List Reference # Quantity Description

1 5 #6-32 × 7/32 in. screws

2 2 #4-48 × ¼ in. screws

3 1 Head Cover Casting

4 1 Clean Out Cover Casting

5 1 Cover Plate

6 3 #6-32 × 7/32 in. screws

7 1 Odometer Bezel Casting

8 1 Front Screen Group

9 2 Spindle Cup

10 2 Flat Washer

11 1 Rewind Spindle & Tire Assembly

12 2 Spindle Cup Tire

13 1 Spindle Cup & High-speed Drum Assembly

14 1 Counter Drive Belt

15 2 Phenol Washer

16 2 ―E‖ Ring, ¼ in. Shaft

17 1 Brake Arm Spring

18 1 Left Brake Arm Assembly 19 1 Right Brake Arm Assembly

20 2 Brake Arm Roller

21 2 Brake Roller Leaf Spring

22 1 Spacer

23 2 Brake Release Link

24 1 Grip Ring


26 1 Rewind Spindle & Arm Assembly

27 1 Rear Slide Cam Assembly

28 1 Right Scissors Detent

29 1 Spring

30 1 Left Scissors Detent

31 1 Spring

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32 1 Rewind Spring

33 1 Counter Worm Shaft & Bracket Assembly

34 1 Counter Assembly

35 2 #8-32 × 5/32 in. Pan Head Screws

36 1 Counter Worm Gear

37 1 Washer

38 1 Grip Ring, 3/16 in. Shaft

39 1 Washer

40 1 Clutch Plate & Felt Assembly

41 1 Take-up Clutch Felt

42 3 Clutch Plate Spring

43 1 Take-up Pulley Assembly

44 3 ―E‖ Ring, ⅛ in. Shaft

45 1 Take-up Belt (WALSCO Part #1410-14)

46 1 Flat Steel Washer

47 1 Flywheel, Capstan, and Hub Assembly

48 1 Steel Ball

49 2 ―E‖ Ring, 3/16 in. Shaft

50 1 Key Return Lever

51 1 Key Return Lever Shaft 52 1 1/16 in. × ⅜in. Roll Pin

53 1 Take-up Actuating Lever

54 1 Take-up Lever Spring

55 1 Motor Pulley

56 1 Set Screw

57 1 Felt Washer

58 1 Slow Idler Assembly

59 1 Slow Idler Slide Assembly

60 1 Slow Speed Idler Spring

61 1 Washer


63 2 Speed Nut

64 1 3¾ ips Speed Change Arm


66 2 Lock Nut

67 2 Large Washer

68 2 Spacer Sleeve

69 3 Thimble

70 3 Grommets

71 2 Small Steel Washer

72 2 Large Steel Washer

73 1 Hex-head Screw

74 1 Steel Washer 75 1 Steel Washer

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76 1 Motor and Plug Assembly, 115VAC, 60 Hz


78 1 Flat Steel Washer

79 1 Motor Fan

80 1 Washer

81 1 Slow Speed Switch Cam


83 1 Cam Actuating Stud Lever Assembly

84 1 ―E‖ Ring

85 1 Bottom Mechanism Plate Assembly

86 3 #8-32 × ¼ Pan Head Screws

87 1 Top Mechanism Plate Assembly


89 1 Pressure Roller Tension Spring

90 1 Function Switching Arm Assembly

91 1 Instant Stop Brake Spring


93 1 Function Roller

94 2 Slide Roller

95 2 ―E‖ Ring, 3/16 in. Shaft 96 1 Instant Stop Brake Arm



99 1 Slide Roller

100 1 Instant Stop Guide Arm


102 2 Fiber Washer

103 1 Pressure Roller Assembly (WALSCO Part #1427-01)

104 1 Instant Stop Arm and Stud Assembly

105 1 Pressure Roller Arm Assembly

106 1 Arm

107 1 High-speed Forward Lever

108 1 Washer

109 1 Spring

110 1 Play Key Assembly

111 1 Record Key Assembly

112 1 Stop Key Assembly

113 1 Key Shaft


115 1 High-speed Idler Spring

116 2 Speed Nut


118 2 Washer 119 2 Idle Slide Assembly

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120 2 Idler Assembly (WALSCO Part #41-040)

121 1 Spring Retainer

122 1 Idler Drive Spring

123 1 7 ½ ips Speed Change Arm



126 1 Two Speed Knob Assembly

127 1 Detent Spring

128 1 Steel Ball

129 1 Cotter Pin

130 1 1/16 in. × ⅜ in. Roll Pin

131 1 Two Speed Arm Shaft

132 1 High-speed Slide & Key Return Lever Assembly


134 1 Key Return Lever Spring

135 1 Brake Release Spring

Monaural Half-Track Head Assembly

136 2 #3-48 × ⅛ in. Screw

137 1 Head Hold-down Spring

138 1 Head Insulator 139 1 Play-Record-Erase Head

140 1 #4-48 Set Screw (for Head Adjustment)

141 2 ―E‖ Ring

142 1 Record Pressure Pad Assembly

143 1 Erase Pressure Pad Assembly

2 Felt Pressure Pads

144 1 Record Pad Spring

145 1 Erase Pad Spring

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Appendix: Early Version Procedures & Components

High Frequency Equalization Adjustment (p. 19) In step 4, you were instructed to adjust the peaking coil for 6 dB (twice the voltage) more output at 10 kHz than at 15 kHz.

Bias Current Adjustment (p. 19) Bias is measured by placing a 100 Ω resistor in series with the record element and

measuring the voltage across this resistor with a meter capable of accurately reading 0.15V @ 70 kHz.

Electrical Components

Tubes & Lights (p. 25)

Early versions used a #47 panel lamp for Lmp1 and a 12AX7 for V1.

Capacitors (p. 25)

Part # Capacitance Voltage Rating

Type

C1 Not used.



C12 100 nF 200V Polyester

C16,C17 Not used.

C37 22 µF 35V Electrolytic

C39 Not used

Resistors (p. 26)

Part # Value Notes

R1 Not used

R30,R48 4.7 Ω 2W wire-wound

R41 82 kΩ

R42 180 kΩ

R44 4.7 kΩ

R46 1.8 kΩ

R47 470 kΩ

Inductors & Transformers (p. 27)

Part # Name Details

T1 Power Transformer Primary: 120V @ 0.4A Sec. 1: 200V @ 7 mA) Sec. 2: 12.6V @0.4A Sec. 3: 6.3V @ ¾A

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T2 Output Transformer Primary Impedance: 8.8 kΩ CT Sec. 1 Impedance: 130Ω CT Sec. 2 Impedance: 8Ω

T3 Driver Transformer Primary Impedance: 25 kΩ Sec. 1 & 2 Impedance: 13 kΩ

T4 Bias Oscillator Coil Different winding inductance.

Switches (p. 28)

Part # Description

S1-S6, S9-S11, S13-S15 Part of Function Slide Switch

S7 Power switch on tone control, SPST

S8 Equalization Switch, SPDT

S12 Mic-Rec/Monitor-P.A. Switch; SPDT

Wollensak T 1500

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