McIntosh MR 55 Owners Manual
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Page 1
The Mclntosh MR-55 is a superior quality AM-FM Tuner for, use in home music systems and profes- sional applications where distortion free reception is needed. Typical professional uses are "off the air" re- cording, broadcast monitor, rebroadcasting, etc. A thorough perusal of this instruction manual will give greater enjoyment and better listening. The MR-55 is the finest tuner available and complete familiarity with its functions and operation will result in the out- standing performance you expect from a Mclntosh product. SPECIFICATIONS: AM Sensitivity: 1.5 microvolts Selectivity: Narrow Position: 4 K.C. Bandwidth, ± 10 K.C. from center down 53 D.B. Medium Position: 13 K.C. Bandwidth, ± 10 K.C. from center down 20 D.B. Broad Position: 20 K.C. Bandwidth (Measurements include R.F. and LF. circuits. Charac- teristics substantially unchanged over entire R.F. tun- ing range.) A.V.C.: Exceptionally strong; less than 4 D.B. audio output change with input changes from 10 microvolts to 100,000 microvolts. Distortion: Less than 1% at 100% modulation Hum: 50 D.B. below full signal Bandwidth: LF. at 600 K.C.-20 K.C.; at 1600 K.C.-20 K.C. R.F. at 600 K.C.-21 K.C.; at 1600 K.C.-23 K.C. Audio Bandwidth: Broad Position ± 3 D.B.-20 to 10 K.C. Medium Position ± 3 D.B.-20 to 6.5 K.C. Narrow Position ± 3 D.B.-20 to 2.0 K.C. Sensitivity Selector: Three Positions Front End: 21 K.C. Constant bandwidth, band pass input Whistle Filter: 70 D.B. rejection 10 K.C. FM Sensitivity: 3 Microvolts at 100% modulation (±* 75 K.C. Dev.) for less than 3% total noise and distortion (Based on I.H.F.M. (proposed) standards for measuring F.M. Tuners) Capture Ratio: 1 to 0.8 I.F. Amplifiers: Four I.F. Bandwidth: 200 K.C.;Flat on Top I.F. Transformers: Mechanically captive Limiters: Two; zero time constant grated-beam followed by a 0.5 microsecond pentode limiter Limiter and Detector Bandwidth: 2 Megacycles Frequency Response: ± 3 D.B.; 20-20,000 cycles Hum: 75 D.B. below full signal A.F.C.: Separate detector; strong, distortion free, com- pletely variable Drift: ± 30 K.C. without A.F.C.: negligible with A.F.C. Antenna Input Impedance: 300 ohm balanced; 72 ohm unbalanced Radiation: Substantially below F.C.C. requirements TUBE V1-6BZ7 F.M. R.F. Amplifier V2-6BZ7 F.M. Reactor and F.M. Os V3-6AB4 F.M. Mixer V4-6BJ6 1st LF. Amplifier V5-6AU6 2nd I.F. Amplifier V6-6Bf6 3rd I.F. Amplifier V8-6AU6 4th LF. Amplifier V7-6AL5 A.M. Detector and A.V.C. Detector V9-6AL5 P.M. A.V.C. V10-6BN6 1st Limiter COMPLEMENT: V11- 6AU6 2nd Limiter V12-6AL5 F.M. Detector V13-6BV8 AFC Detector V14-6BA6 A.M. R.F. Amplifier V15-6BE6 A.M. Converter V16-6AL5 A.V.C. Clamper V17-12AU7 Squelch Amplifier and F.M. Metering V18-12AU7 Audio Amplifier and Cathode Follower SIZE: 4¾ Inches High x 14¾ Inches Wide x 12 Inches Deep WEIGHT: Tuner Only: 17 Pounds, 3 Ounces; In Shipping Carton: 28 Pounds -2-
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INSTALLATION INSTRUCTIONS FOR THE MclNTOSH MR-55 AM-FM TUNER The MR-55 may be mounted in its own cabinet or shelf mounted in a custom cabinet. The tuner has been designed to mount on a shelf rather than hang from the cast tuner panel. Rubber shock mounting feet have been provided to offer the optimum in mechanical isolation from extraneous vibrations. Enclosed in the instruction manual envelope are two copies of the "TUNER PANEL CUTOUT TEM- PLATE" and two copies of the "SHELF MOUNTING TEMPLATE" for mounting the MR-55. Prepare the cabinet for the mounting of the MR-55 by first cutting the wooden cabinet panel to receive the cast tuner panel. 1. On the back of the wooden cabinet panel make a vertical center line on the exact center of the area in which the tuner will mount. Extend this center line to the shelf. 2. Fold the "TUNER PANEL CUTOUT TEMPLATE" on the "FOLD LINE." The "FOLD LINE" is the line of the top of the shelf on which the tuner will mount. 3. Place the "TUNER PANEL CUTOUT TEMPLATE" in the proper location on the inside of the cabi- net with the fold line against the shelf. The template center line should match the center line scribed on the panel in step 1. 4. In the center of the "Cutout Area" on the "Tuner Cutout Template" arc two holes marked "LOCA- TION HOLES." Carefully and accurately drill these two holes with a 5/32 inch drill. 5. Transfer the "TUNER PANEL CUTOUT TEMPLATE" to the front of the wooden cabinet panel. Match the "LOCATION HOLES" for the proper positioning of the template. Proceed with marking the lo- cation of the six holes and the outline of the cutout on the front of the wooden cabinet panel. IMPORTANT: DRILL THE FOUR 3/16 INCH AND THE TWO 5/32 INCH HOLES BEFORE CUTTING OUT THE TUNER PANEL HOLE. The cast tuner panel has a 1/4 inch overlap to cover the edges of the cutout in cabinet panel. Next prepare the shelf for mounting the tuner. 1. Measure the thickness of the wooden cabinet panel. 2. "FOLD LINES" have been supplied on the "SHELF CUTOUT TEMPLATE" for standard pane! thickness up to one inch. Fold on correct fold line for your wooden panel thickness. 4. Place the folded edge of the template against the back of the front panel. The template center line must match the center line extended to the shelf in step #1 of the front panel cutout instructions. 5. Carefully mark the locations of the four 1/4 inch holes and the 8 by 10 1/4 inches, ventillation hole. 6. Drill and cut out the shelf. Next prepare the MR-55 for mounting in the cabinet by removing the pressed wood shipping pallet from the bottom of the tuner. Remove the knobs by gently pulling them toward you. Remove the felt washers. The cast tuner panel has been attached to the tuner by two angle brackets that are for shipping pur- poses only. These are removed by unscrewing the four screws (two on each side) that hold the angle brackets to the tuner chassis. After removing these four screws the tuner panel can be slipped off over the knob shafts. After removing the tuner panel lay it face down on a protected surface for the following operations. Remove the four 6/32 screws (one on each corner) that hold the two shipping brackets to the tuner panel -3-
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FM. TO 300ohm FM ANT. A substitute for the folded dipole can be an existing VHF T. V. antenna. The MR-55 is supplied with an internal switching arrangement that eliminates the need for two set couplers. The VHF T. V. antenna lead-in is connected to the antenna terminals marked "FM. ANT'." Connect the terminals marked "TO T. V. SET" to the antenna terminals on the T. V. receiver with 300 ohm antenna lead. When the MR-55 selector switch is in cither of the "FM" positions the antenna is disconnected automatically from the T. V. receiver. In any other position of the selector switch the antenna is connected to the T. V. set and disconnected from the tuner. TO 300 ohm VHF TV. ANT. TO T.V. SET -6-
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75 OHM UNBALANCED ANTENNA INPUT 75 OHM ANTENNA: The MR-55 has provision for the connection of a 75 ohm unbalanced antenna. The 75 ohm terminal screws are next to the chassis on the back of the brown bakelite balun card located approximately 2 inches behind the tuning knob flywheel. The center conductor of the 75 ohm coaxial lead is attached to the screw terminal located 3/8 inch above the chassis. The outer conductor or ground side is connected to the screw terminal located close to the chassis. Solderless spade lugs are supplied for your con- venience. -7-
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FM - Generator CW- Oscillator 98MC- 75 KC 50cps 90MC- CW-Oscillator Preferably Battery Operated. With Generator Set the Level at 98MC Increase Over, all Gain With External Amplifier If Necessary. Then With CW-Oscillator at 90MC. Measure Hum. Then Switch to Phono and Measure Hum With Phono Input Shorted With 1Mohm. Measure Distortion. Listen 88-98-108MC. 75 KC. Deviation 400cps. Decrease FM-Generator Output for 3% Distortion. Reading of Generator Then Is Measure of Overall Sen- sitivity. Increase Generator Output Until 1 Div. or Sensitivity Meter Is Reached. Generator Output Reading Now is Measure of Gain in RF and IF Stages. Tune/Listen FM - Generator 98MC 75KC. Deviation 400cps. AFC-Conrrol Fully Clockwise Distortion Analyser Audio Output R81 and Upper Slug of T12 for Center of FM-Meter Vary Tuning Knob Until FM-Meter Remains Stationary. For Tune and Listen Positions With R81, Bring FM-Meter to Center, With Selector Switch in Tune Position. Decrease Output FM-Generator Until 3% Distortion and Noise Is Found. Then in Listen Position, Adjust T12 for Minimum Distortion and Noise. Overall Tune FM - Generator Center Freq's. 88- 108MC. 75 KC. Deviation 50cps. Thru Balun to Antenna Input, or 75ohm Input With Termi- nating Resistors Oscilloscope, Synchronized to Input Sweep Test Point T3 > Upper and Lower Slugs T5 > for Best Response Curve Vary Freq. From 88 to 108MC. and Follow With Tuner, for Gesf Response Curve Over FM-Band. Give Special Attention to 96.3MC for Interference of 9 x 10.7MC. IF-Strip Tune CW - Oscillator 10.7MC. Point (R) (Pin 6-V3) Oscillator Coupled to (H) Thru .0! MF Condenser and Terminating -Resistance. V.T.V.M. Test Point T2 T3 Upper and lower Slugs T5 for Maximum T7 T9 Defeat AVC-Action at Point J (R36-R38) Load Transformer-Winding No! Under Adjustment - with 10Kohm Resistor Front-End Tune SWEEP GENERATOR CW- Oscillator Center Freq's. 88- 108MC. 90 and 105MC. Thru Balun to Antenna input or 75ohm input With Termi- nating Resistors Any Suitable Injeclion- Point To Be Used as 90- 105MC, Marker Points Oscilloscope, Synchronised to Input Sweep FM-Tuning Meter Point (G) ( Pin 7-V3 ) L9 - C18 - L10 - C19: For Best Response, Keeping 90-1 05MC. Markers in Corres- pondence With the 90 - I05MC. Dial Points L11 - C23: For Calibrating the Tuner FM- Local-Oscillator to 90 - 105MC. Dial Points Adjustments of LP-C18-L10-C19 and L11-C23 Are Inter Related, Therefore Both Series of Adjustments Should Be Checked and Rechecked. Disable the Oscillator When Adjusting L9-C18-L10-C19 Point (E) (Pin 5-T12) T12: Lower Slug for Man. R81 : For FM-Tuning- Meter Center TI2: For FM-Tuning-Meier Center Ground Point F ( High Side R82) 10.7MC Point (C) (Pin 7-V12] Point (D) (R70-C88) T11 : Lower Slug for Max. Upper Slug for Zero 10.4MC. T10: Upper Slug for Max. Lower Slug for Max. Load Primary With 1.5Kohm Resistor Load Secondary with 1.5Kohm Resistor Limiters, Detector and Audio Tune CW- Oscillator 10.7MC. Point (A) (Pin 5- V9) Oscillator Coupled to (A) Thru .01 MF Condenser and Terminating Resistor, V.T.V.M. Point (B) (Pin 1-V11) R63: For Max. 100Kohm Resistor in Series With D.C. Probe of V.T.V.M. CIRCUIT UNDER TEST POSITION OF SEL SW. SIGNAL GENERATOR FREQUENCY AT SIGNAL-SOURCE REMARKS MEASURED WITH AT ADJUST SIGNAL-OUTPUT REMARKS F.M.