McIntosh MC275LE Service Manual
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McIntosh MC275LE Service Manual

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Table of Contents

Performance Specifications ..........................................2
Notes ...........................................................................2
Section Location ..........................................................3
Block Diagram .......................................................5 - 6
Interconnection Diagram ........................................7 - 8
Main Schematic and PCB .....................................9 - 22
Terminal Schematic ...................................................18
Terminal PCB......................................................23 - 24
SERVICE MANUAL
MC275LE
POWER AMPLIFIER
ALL SERIAL NUMBERS
CONTENTS
Handcrafted in USA with US
and Imported Parts
Amplifier Schematic ...........................................25 - 28
Balanced Input / Unbalanced Input /
Power Control / Tube Light Schematic .................29 - 30
Amplifier / Balanced Input / Unbalanced Input /
Power Control / Tube Light PCB ..........................31 - 34
Parts List .............................................................37 - 46
Repacking Instruction ................................................47
MC275LE

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Summary of Contents for McIntosh MC275LE

  • Page 1: Table Of Contents

    MC275LE MC275LE POWER AMPLIFIER ALL SERIAL NUMBERS Handcrafted in USA with US and Imported Parts CONTENTS Performance Specifications ..........2 Amplifier Schematic ...........25 - 28 Notes ................2 Balanced Input / Unbalanced Input / Section Location ............3 Power Control / Tube Light Schematic ....29 - 30 Block Diagram ............5 - 6...

  • Page 2: Performance Specifications

    240V ~ 50/60Hz at 1.8 Amps 250 milliwatts to rated power, 20Hz to 20,000Hz Standby: Less than 0.3 watts Note: Refer to the right side panel of the MC275LE for the Frequency Response correct voltage. +0, -0.5dB from 20Hz to 20,000Hz Overall Dimensions +0, -3.0dB from 10Hz to 100,000Hz...

  • Page 3: Section Location

    MC275LE SECTION LOCATIONS...
  • Page 4 NOTES...

  • Page 5: Block Diagram

    MC275LE BLOCK DIAGRAM 12AX7A L OUTPUT 12AX7A 12AT7 L BALANCED BALANCED INPUT BUFFER 12AX7A 12AT7 PHASE BUFFER INVERTER L UNBALANCED INPUT MODE SWITCH SWITCH R/MONO UNBALANCED AUDIO DETECTOR R OUTPUT 12AX7A 12AX7A 12AT7 INPUT R/MONO BALANCED BALANCED BUFFER 12AX7A 12AT7...
  • Page 6 INPUT MAIN INPUT TERMINAL WHT/YEL WHT/YEL RIGHT LEFT MC275LE TRANSFORMER WIRING AND FUSE REPLACEMENT (CONTACT MCINTOSH FOR CORRECT TRANSFORMER P/N) Voltage BLK BLK/GRY GRY VIO WHT/VIO BRN 1 BRN 2 Jumper Location (JMP1) Main Fuse (F1) T6.3AL250V T5AL250V T5AL250V T3.15AL250V INPUT T3.15AL250V...
  • Page 7 MC275LE MAIN 751261 SCH 1 of 3 +12V J1:1 VOUT J1:4 350mA 100V 220µF 110V JMP 1 120V J1:7 PRI MARY J1:10 +12.6V J2:1 +700V J2:4 220V 230V 2.2k 240V J2:7 +480V +350V J2:10 46.4k +12V 6-32 J5:2 TEST ONLY 680µF...
  • Page 8 MAIN 751376 SCH 1 of 3 +12V J1:1 VOUT J1:4 350mA 220µF 100V 110V JMP1 120V J1:7 PRIMARY J1:10 +12.6V J2:1 +700V J2:4 220V 230V 240V J2:7 2.2k +480V +350V J2:10 46.4k +12V 6-32 J5:2 TEST ONLY 680µF 47µF NO CONNECTION APPLY 12VDC TO ENERGIZE RELAYS J5:1...
  • Page 9 MC275LE MAIN 751261 SCH 2 of 3 POWER UP TURN ON UNBAL DELAY CONTROL INP SW J26:2 J30:5 INPUT J30:6 AUTO OFF TIM ER 2.21M 47.5 47.5 PC GND J26:1 J30:8 J30:9 PC ON TUBE LT J30:3 .1µF MONO 100K 22.1K...
  • Page 10 MAIN 751376 SCH 2 of 3 POWER UP TURN ON UNBAL DELAY CONTROL INP SW J26:2 J30:5 INPUT AUTO OFF J30:6 DISABLED AUTO OFF TIM ER INDICATOR 2.21M 47.5 47.5 PC GND J26:1 J30:8 J30:9 PC ON TUBE LT J30:3 .1µF MONO 100K...
  • Page 11 MC275LE MAIN TERMINAL 751261/751376 SCH 3 of 3 751379 SCH V9 PLT J32:6 L AUDIO TRANSFO RMER V8 CATH J32:10 V8:1 KT88 V8 GRID J32:9 220 5W L OUT 16 FIL C J32:13 L 16(+) FIL C 1µF 2200pF KT88...
  • Page 12 MAIN 751261 PCB...
  • Page 13 MC275LE MAIN 751376 PCB...

  • Page 14: Terminal Pcb

    TERMINAL 751379 PCB...
  • Page 15 MC275LE AMPLIFIER 751262 SCH 1µF V9 PLT J5:6 +350V +700V 200V .047µF V8 CATH J5:10 V8 CATH L BAL+ 22.1k J1:2 L BAL+ V1:1 L OUT 16 12AT7A .047µF L BAL- 100k 3.32K 100k V8 GRID J1:1 L BAL- J5:9...
  • Page 16 AMPLIFIER 751377 SCH 1µF V9 PLT J5:6 +350V +700V 200V .047µF V8 CATH J5:10 V8 CATH L BAL+ 22.1k J1:2 L BAL+ V1:1 L OUT 16 12AT7A .047µF L BAL- 100k 3.32K 100k V8 GRID L BAL- J5:9 J1:1 V2:1 12AT7A 100pF V3:2...
  • Page 17 MC275LE BAL INPUT UNBAL INPUT PWR CNTRL TUBE LT 751262 SCH 751262 SCH 751262 SCH 751262 SCH 751377 SCH 751377 SCH 751377 SCH 751377 SCH PC IN J8:1 PC IN J13:12 PC GND J13:4 J13:5 TUBE LT J13:10 Power Control...
  • Page 18 BAL INP UNBAL INP PWR CTRL TUBE LT 751262 PCB 751262 PCB 751262 PCB 751262 PCB 751262 PCB...
  • Page 19 MC275LE BAL INP UNBAL INP PWR CTRL TUBE LT 751377 PCB 751377 PCB 751377 PCB 751377 PCB 751377 PCB...
  • Page 20 NOTES...

  • Page 21: Parts List

    INTERCONNECT Ref. No. Description Part No. Ref. No. Description Part No. CAP ELECT 47UF 450V 066560 MCINTOSH BINDING POST 084226 CAP MONO .1UF 50V 20% SMD0805 061365 MCINTOSH BINDING POST 084226 CAP MONO .1UF 50V 20% SMD0805 061365 MCINTOSH BINDING POST 084226 CAP MONO .1UF 50V 20% SMD0805...
  • Page 22 PARTS LIST (Cont’d.) MAIN PCB 751261 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. TRANSISTOR NPN 60V MMBTA05LT1G SMD 132333 DIODE SMALL SIGNAL 4148 SMD 070199 TRANSISTOR PNP 60V MMBTA55LT1G SMD 132334 DIODE SMALL SIGNAL 4148 SMD 070199 TRANSISTOR NPN 60V MMBTA05LT1G SMD 132333 DIODE SMALL SIGNAL 4148 SMD...
  • Page 23 MC275LE PARTS LIST (Cont’d.) MAIN PCB 751261 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. IC DECADE COUNTER SMD 133794 RES SMD0805 100K 1/8W 1% 145014 IC SINGLE NAND SCHMITT SMD 133724 RES SMD0805 100K 1/8W 1%...
  • Page 24 PARTS LIST (Cont’d.) MAIN PCB 751376 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. CAP MONO .1UF 50V 20% SMD0805 061365 BLADE FASTON .250 117708 CAP MONO .1UF 50V 20% SMD0805 061365 BLADE FASTON .187 117726 CAP MONO .1UF 50V 20% SMD0805 061365 BLADE FASTON .187 117726...
  • Page 25 MC275LE PARTS LIST (Cont’d.) MAIN PCB 751376 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. FUSE 0.35A 16V RESET 1206 SMD 145054 RES MO 30K 5% 2W 144602 POLYSWITCH 8A 30V 144750 RES MO 30K 5% 2W 144602 POLYSWITCH 3.00A 72V...
  • Page 26 PARTS LIST (Cont’d.) MAIN PCB 751376 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. DIODE SMALL SIGNAL 4148 SMD 070199 SOCKET OCTAL TUBE CERAMIC 178196 DIODE SMALL SIGNAL 4148 SMD 070199 SOCKET OCTAL TUBE CERAMIC 178196 DIODE SMALL SIGNAL 4148 SMD 070199 AMPLIFIER PCB 751262 DIODE SMALL SIGNAL 4148 SMD...
  • Page 27 MC275LE PARTS LIST (Cont’d.) AMPLIFIER PCB 751262 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. MP18 RETAINER LITEPIPE LED 078045 RES MF 150K 1% 1/4W 144627 RES SMD0805 22.1K 1/8W 1% 145012 MP19 LITEPIPE LED 0.8L X 0.1 DIA...
  • Page 28 PARTS LIST (Cont’d.) AMPLIFIER PCB 751377 Ref. No. Description Part No. Ref. No. Description Part No. CAP ELECT 10UF 250V 066558 DIODE SMALL SIGNAL 4148 SMD 070199 DIODE SMALL SIGNAL 4148 SMD 070199 CAP ELECT 100UF 25V 066573 CAP ELECT 100UF 25V 066573 DIODE SMALL SIGNAL 4148 SMD 070199...
  • Page 29 MC275LE PARTS LIST (Cont’d.) AMPLIFIER PCB 751377 (Cont’d.) Ref. No. Description Part No. Ref. No. Description Part No. TRANSISTOR PNP 300V BF421 132352 RES SMD0805 22.1K 1/8W 1% 145012 TRANSISTOR PNP 300V BF421 132352 RES SMD0805 22.1K 1/8W 1% 145012...
  • Page 30 PARTS LIST (Cont’d.) TERMINAL PCB 751379 TERMINAL PCB 751379 Ref. No. Description Part No. Ref. No. Description Part No. CAP POLYPROP 0.15UF 10% 275V 064464 RES WW 4 OHM 5% 5W 139248 CAP POLYPROP 0.15UF 10% 275V 064464 RES WW 4 OHM 5% 5W 139248 BLADE FASTON .187 117726...

  • Page 31: Repacking Instruction

    400131 10-32 x 1/2 inch screw part(s) are needed, please call or write Customer 163073 Feet Service Department of McIntosh Laboratory. Refer to page 3. Please see the Part List for the correct part numbers. TUBE COVER FOAM PAD WITH TUBE...
  • Page 32 The continuous improvement of its products is the policy of McIntosh Laboratory Incorporated, who reserve the right to improve design without notice. Because of the constant upgrading of McIntosh products’ circuitry and components, the Company cannot insure, and does not warrant, the accuracy of the within schematic material, which is intended for information only.

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