Sonar T-10 Schematic

Sonar T-10

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The Sonar Tape Recorder Model T - in is high fidelity equipment composed of four basic units; namely the RPA - in Amplifier, the PS - 300 Power Supply, the Tape Mechanism and the infinite Impedance Speaker System.
The T - in Recorder is designed for 117 volt 60 cycle operation. Before applying power, be sure current outlined above.

Toggle switch on the front panel marked " disc-tape " should be in " Disc " position until the operator is thoroughly familiar with the operation of the amplifier.

OPERATION: Piug the two cables found in the in the rear of recorder case into the matching receptacles of power supply and speaker enclosure, respectively. Turn the control marked " speaker-gain " until a click is heard. This is the the main power switch When the power is on, the " Listen " indir cater light will glow, 1 If the " Record " indicator light is on, turn the " Listen Record " switch to the " Listen " position Permit the amplifier to warm up for one minute before using.
Remove the red wing screw on top of the tape unit before using.
using. This wing screw should be re-inserted when carrying the recorder and removed when put in operation.

INPUTS: There are four inputs on the front panel designated as LG: I low gain 1), LG2 Tlow gain 21, " Mike l " and " Mike 2 " Control marked " Gain | controls counter-clockwise rotation from " O and " Mike clockwise rotation. Control marked " Tape Gain " controls LG2, counter clockwise rotation from "0"; playback of

Tape, clockwise rotation. When the " Listen Record " switch is in the " Record " position, clockwise rotation of " Tape Gain " control then controls " Mike 2 " input. Control marked " Speaker Gain'is completely independent of " Gain 1 " control and " Tape Gain " control, and may be set to any desired level for playback or monitoring while recording.
When using LGT and LG2, a wide range of impedances from 100 ohms to 500,000 ohms may be used without the need of a matching transformer. Microphone inputs are high impedance and will handle microphone signal from - 650B. When using low impedance microphones, a cable trans former should be employed.
Any combination of inputs such as FM AM radio,
phonograph, etc., should be fed LGI or LG2. Microphones or Reluctance pickups should be fed to Mike | or Mike 2. Any combination of the above may be electronically mixed.
A fifth input located on top of the chassis,
as noted in Figure 1,
titled " Dubbing is to connect two tape recorders together for simultaneous recording. Dubbing one tape to another, or playing two tape machines simultaneously, may be achieved. A low gain signal, such as a radio having its volume control, may be fed to this fifth input without having to use any of the front pane i mixing controls.
Frequency equalization for the cording amplifier is fixed. The " Bass " and " Treble controls only affect the reproduced signal as heard through the speaker system. The bass control will boost 20DB and cut 20DB. The treble control will boost 15DB and cut 15DB.
For so-called fiat frequency response, the bass control should be set to # 2 and the treble control to # 3. The operator, however, could set these equalizers to suit his particular desires.

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OPERATION OF TAPE MECHANISM: Place empty tape reel left hand spindle, keyed side down, so that key fits in drive pin on spindle.
Place loaded tape reel on right hand spindle, keyed side down, So that key fits in drive pin on spindle. Tape must come off reel, clockwise, with coated surface out. (Black side of paper tape is the coating. Dull side of plastic tape is the coating.). Jf coating is in side, put a half twist in the tape before threading. When loaded tape reel is wound | up on the take-up reel, rethread the right hand reel with coating outside. Place left control knob, which controls the threading of tape, toward rear of case. This leaves the tape slot in the escutcheon open for threading. (See Control Sketch, Figure 2.)
Slowly draw several feet of tape offi the loaded reel, through the slot in the escutcheon, keeping it taut against the drag of clutch, and allowing enough tape to thread and wrap on the unloaded reel. See that tape is not twisted.
Pull left control knob toward front of case. This threads the tape against the capstan and tape guides. it also holds the tape in place while the balance of the operation is completed, that is, winding a couple of wraps on the empty reel, Tape is inserted in slot in reel center and wrapped on clockwise by rotating the reel by hand. Care must be taken to insure that the tape is not twisted.

Plug in a microphone in either Mike or Mike 2, or a low level signal, such a radio, to LGI to LGI or LG2. Set toggle switch from Disc to Tape and adjust the gain control corresponding to the input being used so the V.U. Meter will move with program material and will read a peak value of " O " once every few seconds to a minute, depending upon the nature of the program being recorded. Adjust " Speaker. Gain " control to desired monitoring level. if a microphone is used, care should be taken to prevent a howl. Set the " Listen - Record switch the " Record " position.

Start tape in forward position by pushing right hand control forward (to ward rear of case).
To record on the Tower track, pull the right hand control toward the front of the case.

Set the Listen - Record " switch in the " Listen " position. Shut the V.U. Meter off. Adjust tape-gain control to # 3 clockwise rotation. Start the tape ma chine as outlined under Recording, and adjust speaker-gain control and equalizer to desired volume and tone, respectively. The V.U. Meter may be used to read the playback level on the tape. Adjust tape gain control so that the V.U. Meter does not read above + 3 V.U.

When recording, the tape is automati- cally erased. However, to erase a certain section of tape on either track,
set controls marked " Gain 1 " and " Tape Gain " to " O
and put the " Listen - Record " switch in the " Record " position. Start tape in motion dependent on track to be erased. Forward direction erases top track.
Reverse direction erases bottom track.

if it is desired to rewind the tape before completing one channel in playback or recording, all that is necessary is to first reverse the direction of tape, and then unthread the capstan and tape guides by moving the left hand. centre i toward the rear of the case, or into the unload position. This releases the drag on the tape and the clutches pick up speed.
When tape is completely rewound, or rewound to the point desired, place the right hand control in neutral STOP E position.

NOTE: When rewinding in the reverse direction, it may be necessary to rotate the right hand take-up reel by hand when the reel is three quarters loaded. This is normal, since the clutches are set to give, accurate timing at 7.5 " per second, in record and playback of tape on on both tracks.

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When tape mechanism is not in use, make sure the left hand control is towards the rear of case. This is to prevent the record playback head from resting on the capstan, causing " flats ". Before engaging the left hand control, take up tape slack by rotating either ree by hand.

AUTOMATIC REWIND: Wind the tape the forward or clockwise direction onto the left hand reel where the program on the tape ends, Place a one inch piece of 4 " wide aluminum foil adhesive tape on the back (un coated sidel of tape.
Rewind tape in reverse direction back onto right hand reel, The machine is now ready for playing or recording two tracks automatically. The aluminum foil actuates a solenoid switch which is composite with the first tape guide at the right end of the forward escutcheon.

The Sonar T - in Tape Recorder will play tapes made on single track machines when operated in the forward direction. Single track recordings made on the T - in Recorder, forward direction, may be played on any other single track recorder.

MONITORING: A jack mounted on the front panel titled " Monitor is designed to feed a pair of earphones, high or low impedance. The monitor output can also feed a booster amplifier or a telephone line when fed to a matching transformer having impedances of 100,000 ohm Pri, and 600 ohm Sec. The speaker gain control has no effect on the monitor level. The monitor level is controlled by controis marked " Gain " and " Tape Gain ".

Since the RPA - in Amplifier is a high fidelity unit, having a conservative rating of in watts output with exception ally low harmonic distortion, it can be used for disc recording. The power out put may be fed to a magnetic disc recording head. Simply determine the cutter impedance and connect to the power output having the corresponding impedance. The

Output transformer in the RPA - in Amplifier is wired for in ohms and 500 ohms output, as noted in the schematic. How ever, any other impedance may be obtained since the secondary is of the multi-impedance type. The V.U. Meter may also be used as a cutting level indicator, connecting the unused side of the toggle switch through a high resistance to the 500 ohm line. The exact value of resista ance will be determined by finally obtaining the proper recording level on the disc and then setting the resistor $ o the meter reads " O " V.U. Do not disturb the V.U. Calibration control on top of the chassis.

AS will be noted from the schematic diagram, the RPA - in Amplifier has tubes, five of which are dual purpose triodes. The pre-amplifier section uses two 12S17 tubes and one 125C7 tube. These three tubes have D.C. voltage on their filaments, cbtained from the cathodes of the 616 output tubes. The three tubes in the high gain pre-amplifier and low gain input circuits are purposely operated at reduced filament voltage to give a better signal-to-noise ratio.
The 65J7 tube is the tape recording amplifier having the necessary equalization in the grid circuit. This stage gets the signal from the plates of the 125C7 tube, The 12SC7 tube also feeds the 6SN7 - Itube used volume indicator stage working the V.U. Meter. The 6SL7 stage also gets its signal from the 125C7 - tube. This 6SL7 stage is a voltage amplifier that feeds the high and low frequency equalizers. The other half of the tube feeds the monitor. The output of the equalizer feeds one half of the 6SN7 tube which is directly coupled to the second half of the tube, functioning as a plate cathode phase inverter, driving the 6L6's elin push-puil. Inverse feedback is em-ployed between the 500 ohm output wind eling and the 6SN7 driver tube. This feed-pack enables large power output with good - Tregulation and low harmonic distortion.
The bias and erase circuits + 6SN7 tube as the 70 K.C. oscillator and bias amplifier. Bias amplifier has

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Adjustable control mounted on the rear skirt of the chassis. The erase amplifier circuit uses a 6V6 tube to insure better than 55DB erasure.

The power supply uses a 5U4G rectifier tube feeding two separate filter sections, as noted in the schematic diagram.
There are two B + outputs, one for the 6L6 plates, the other for the voltage amplifiers and bias oscillator and amplifier. The power supply delivers 200 mils at approximately 370 volts out of the single choke section filter, and approximately 360 volts out of the two section choke filter. A 6.3 volt filament supply at 5 Amps. and 5 volts at 3 Amps.
Power supply has an A.C. outlet mounted lon the side of the chassis to feed tuner, or where A.C.
outlet may be required that is controlled from the amplifier A.C. switch. A 5 amp. type 3AG fuse is included in the power supply for line protection.

84 voltage fed to the primary center tap of the output transformer is 370 volts. B + measured from the screens of the 6L6 tubes is 360 volts. These volt ages are measured with the " Listen - Record " switch in the " Listen
" Listen position. With the " Listen - Record " switch in the " Record position, the voltages will be 350 and 320, respectively.
The erase voltage, with the tape ma chine running and the " Listen - Record " switch in the Record " position, is 250 volts.
The bias voltage is set for 125 volts.
with the 6SN7 oscillator tube removed, feed a 5000 cycle tone into the amplifier, adjust the the gain control for 5 volts, measured at the record playback head. Then ad just the V.U. Meter Control for " O " V.U. deflection.

All voltages measured with V.T.V.M. The bias and erase voltages are measured with a probe feeding the V.T.V.M Sonar Tape Recorder, Model T - 10, oc, casionally will require minor adjustments to the tape mechanism, Depending on the use of this machine,
it is advisable that the capstan be cleaned once a mont with 370 sand paper. This is to insure proper traction at all times, One method of checking the traction between the capstan and the tape is to Toad the machine as outlined under " Operation of Tape Mechanism ". Running in the forward direction, gently grab the right-hand spool. This will cause the left-hand knob to move forward, indicating proper tension.
The siipping clutches employed in this mechanism should be set and maintained to produce 3 to 4 ounces tape tension. This tension is measured with a vest pocket type postal scale, Fasten the leader coming from the tape to the scale, keeping the mechanism in the " Off " position, and draw the scale until the reel starts to turn. This will show the amount of tension on the tape. To increase or decrease this tension, there is provided a Tocking nut mounted directly on the bot tom of each slipping clutch. Turning the nut counter-clockwise increases tension, clockwise rotation decreases tension.
Approximately once every three months, the two erase heads and the record play back head should be cleaned by dipping a pipe cleaner into carbon tetrachloride and swabbing the gaps of oxide that wil normally accumulate. Permit the heads to dry for at least five minutes before using. Do not put carbon tet on the capstan,
It is also advisable, approximately once every month, to clean the flywheel with a rag soaked in carbon tet,
and also the two rear discs representing the slipping clutches,

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