SERVICE MANUAL

Performance Specifications ........................................ 2Notes ......................................................................... 2Rear Panel .................................................................. 3Section Location ........................................................ 4Block Diagram ........................................................... 5Interconnection Diagram ...................................... 7 - 8

Amplifier Schematic and PCB ............................. 9 - 12Input Schematic and PCB .................................. 13 - 14Parts List ............................................................ 15 - 16Exploded View and Parts List ............................. 17 - 18Repacking Instructions ............................................. 19

CONTENTS

STEREOPOWER AMPLIFIERSTARTING WITH SERIAL NO. WV1536

PERFORMANCE SPECIFICATIONS

2

1. The heavy lines on the schematic denote the primarysignal path.

2. Unless otherwise noted, all voltages indicated on theschematics are measured under the following conditions:a. AC input at 120 volts, 50/60Hz.b. All voltages are +/-10% with respect to ground. A

high impedance (10 megaohm) voltmeter must be used.

3. Unless otherwise specified:a. Resistor values are in ohms.b. Capacitor values are microfarads (uF).c. Inductor values are in microhenries (uH).

4. On PC board drawings, Square pad indicates:a. Polarized Capacitors - Positiveb. Diodes - Cathodec. Others - Pin 1

5. WARNINGParts marked with the symbol have criticalcharacteristics. Use only replacement parts recom-mended by the manufacturer.

NOTES

Power Output StereoMinimum sine wave continuous average power outputper channel, both channels operating is:75 watts into 4, 8 or 16 ohm load

Power Output Mono (Parallel)Minimum sine wave continuous average power outputis:150 watts into 2 ohm, 4 ohm or 8 ohm load

Output Load Impedance4, 8, or 16 ohm (Stereo Mode)2, 4, or 8 ohm (Mono Mode)

Rated Power Band20Hz to 20,000Hz

Total Harmonic DistortionMaximum Total Harmonic Distortion at any power levelfrom 250 milliwatts to rated power output is 0.5%

Intermodulation DistortionMaximum Intermodulation Distortion if instantaneouspeak output per channel does not exceed twice the ratedoutput, for any combination of frequencies from 20Hz to20,000Hz, with both channels operating is 0.5%

A-Weighted Signal To Noise Ratio100dB

Frequency Response+0, -0.5dB from 20Hz to 20,000Hz+0, -3dB from 10Hz to 70,000Hz

Sensitivity1.2 Volt unbalanced inputs2.5 Volt balanced inputs

Wide Band Damping FactorGreater than 14

Input Impedance90,000 ohms unbalanced180,000 balanced

Tube Compliment3 - 12AX7A Inputs and Phase Inverters4 - 12AT7 Voltage Amplifier and Drivers4 - KT88/6550 Power Output

Power Requirements100 Volts, 50/60Hz at 360 watts110 Volts, 50/60Hz at 3.6 amps120 Volts, 50/60Hz at 3.6 amps220 Volts, 50/60Hz at 1.8 amps230 Volts, 50/60Hz at 1.8 amps240 Volts, 50/60Hz at 1.8 ampsNote: Refer to the right side panel of the MC275 for the correctvoltage.

Overall DimensionsWidth is 16-1/2 inches (41.91cm), Height is 8-1/4 inches(20.96cm) including feet, Depth is 12 inches (30.48cm)

Weight67 pounds (30.5kg) net, 75 pounds (34.lkg) in shippingcarton

3

SECTION LOCATIONS

BOTTOM VIEW WITH COVER REMOVED

TOP VIEW WITH COVER REMOVED

TERMINALBLOCK

AMPLIFIERPCB 2

INPUTPCB 3

KT88 (4X)

OUTPUTTRANSFORMER 1

POWERTRANSFORMER 1

12AT7

12AT7

12AX7A

12AX7A

CHOKEFILTER

MC275

BLOCK DIAGRAM

4

5 6

MC275

INTERCONNECT1

7 8

AMPLIFIER 7506752A

AMPLIFIER 7506752B

9 10

AMPLIFIER 7506752

MC275

11

INPUT 7500823

12

13

PARTS LISTMC275

1

2

Ref. No. Description Part No.INTERCONNECTF1 FUSE 4A 250V SLO-BLO 5X20 IEC 089135L1 CHOKE FILTER 0.5H 800MA SLOTS 122379RT1 ASSEMBLY THERMISTOR CL-40 5R 052008S1 CABLE ASSY PWR SWCH 171729T1 POTTED TRANSFORMER POWER 750086T2 POTTED TRANSFORMER OUTPUT 750085T3 POTTED TRANSFORMER OUTPUT 750085

750675 AMPLIFIER PCBC1 CAP ELECT 47UF 450V 066560C2 CAP MPF 0.1UF 630VDC 064431C3 CAP MPF 0.1UF 630VDC 064431C4 CAP ELECT 100UF 25V 066573C5 CAP ELECT 100UF 25V 066573C6 CAP MPF 0.1UF 5% 63VDC 064325C7 CAP MPF 0.1UF 5% 63VDC 064325C8 CAP MPF 0.1UF 5% 63VDC 064325C9 CAP MPF 0.1UF 5% 63VDC 064325C10 CAP ELECT 470UF 16V 066508C11 CAP ELECT 470UF 16V 066508C12 CAP PF 0.001UF 5% 63VDC 064453C13 CAP PF 0.001UF 5% 63VDC 064453C14 CAP MPF 0.0022UF 5% 63VDC 064454C15 CAP MPF 0.0022UF 5% 63VDC 064454C16 CAP MPF 0.1UF 630VDC 064431C17 CAP MPF 0.1UF 630VDC 064431C18 CAP MPF 0.1UF 630VDC 064431C19 CAP MPF 0.1UF 630VDC 064431C20 CAP ELECT 470UF 50V 066469C21 CAP ELECT 470UF 50V 066469C22 CAP POLYPROP 0.22UF 20% 1KVDC 064432C23 CAP POLYPROP 0.22UF 20% 1KVDC 064432C24 CAP POLYPROP 0.22UF 20% 1KVDC 064432C25 CAP POLYPROP 0.22UF 20% 1KVDC 064432C26 CAP POLY .047UF 10% 1000VDC 064434C27 CAP POLYPROP .047UF 10% 250VDC 064364C28 CAP ELECT 680UF 315V 066549C29 CAP ELECT 680UF 315V 066549C30 CAP ELECT 4700UF 35V 066541C31 CAP ELECT 680UF 315V 066549C32 CAP ELECT 680UF 315V 066549C33 CAP ELECT 47UF 450V 066560C34 CAP ELECT 47UF 450V 066560C35 CAP ELECT 47UF 450V 066560C36 CAP MPF 0.22UF 5% 63VDC 064329C37 CAP MPF 0.22UF 5% 63VDC 064329D1 DIODE ZENER 200V 1.5W 070177D2 DIODE ZENER 200V 1.5W 070177D3 DIODE ZENER 200V 1.5W 070177D4 DIODE ZENER 200V 1.5W 070177D5 DIODE ZENER 200V 1.5W 070177D6 DIODE ZENER 200V 1.5W 070177D7 DIODE ZENER 200V 1.5W 070177D8 DIODE ZENER 200V 1.5W 070177D9 DIODE ZENER 200V 1.5W 070177D10 DIODE BRIDGE RECT 1000V 6A 070180D11 DIODE SIL 400 PIV @ 1.5A 070031D12 DIODE SIL 400 PIV @ 1.5A 070031D13 DIODE RECTIFIER 070178D14 DIODE RECTIFIER 070178

F1 FUSE 2A 250V SLO-BLO 5X20 IEC 089123F2 FUSE 2A 250V SLO-BLO 5X20 IEC 089123F3 FUSE T8AL 250V SLO-BLO 5X20 IEC 089134F4 FUSE T8AL 250V SLO-BLO 5X20 IEC 089134J1 CONN MALE 6 POS FRICTION LOCK 117218J2 CONN 3 POS MALE MTS100 NORMAL 117214J3 CONN 3 POS MALE MTS100 NORMAL 117214J4 BLADE FASTON W/FEET 117708J5 BLADE FASTON W/FEET 117708J6 BLADE FASTON W/FEET 117708J7 BLADE FASTON W/FEET 117708J8 BLADE FASTON W/FEET 117708J9 BLADE FASTON W/FEET 117708J10 BLADE FASTON W/FEET 117708J11 BLADE FASTON W/FEET 117708J12 BLADE FASTON W/FEET 117708J13 BLADE FASTON W/FEET 117708J14 BLADE FASTON W/FEET 117708J15 BLADE FASTON W/FEET 117708J16 BLADE FASTON W/FEET 117708J17 BLADE FASTON W/FEET 117708J18 BLADE FASTON W/FEET 117708J19 BLADE FASTON .187 117726J20 BLADE FASTON .187 117726J21 BLADE FASTON W/FEET 117708J22 BLADE FASTON W/FEET 117708J23 BLADE FASTON W/FEET 117708J24 BLADE FASTON W/FEET 117708J25 BLADE FASTON W/FEET 117708J26 BLADE FASTON W/FEET 117708J27 BLADE FASTON W/FEET 117708J28 BLADE FASTON W/FEET 117708J29 BLADE FASTON W/FEET 117708J30 BLADE FASTON W/FEET 117708J31 BLADE FASTON W/FEET 117708J32 BLADE FASTON W/FEET 117708L1 CHOKE 2.2 UH 122405L2 CHOKE 2.2 UH 122405L3 CHOKE 2.2 UH 122405L4 CHOKE 2.2 UH 122405R1 RES MF 1M 1% 1/4W 144577R2 RES MF 1M 1% 1/4W 144577R3 RES MF 221K 1% 1/4W 144629R4 RES MO 100K 5% 2W 144698R5 RES MO 100K 5% 2W 144698R6 RES MF 221K 1% 1/4W 144629R7 RES MF 221K 1% 1/4W 144629R8 RES MF 221K 1% 1/4W 144629R9 RES MF 1K 1% 1/4W 144513R10 RES MF 1K 1% 1/4W 144513R11 RES MF 100K 1% 1/2W 144635R12 RES MF 100K 1% 1/2W 144635R13 RES MF 1M 1% 1/4W 144577R14 RES MF 1M 1% 1/4W 144577R15 RES MF 1M 1% 1/4W 144577R16 RES MF 1M 1% 1/4W 144577R17 RES MF 10K 1% 1/4W 144504R18 RES MF 10K 1% 1/4W 144504R19 RES MF 10K 1% 1/4W 144504R20 RES MF 10K 1% 1/4W 144504R21 RES MF 100 OHM 1% 1/4W 144568R22 RES MF 100 OHM 1% 1/4W 144568

Ref. No. Description Part No.

14

PARTS LIST con’t

3

R23 RES MF 100 OHM 1% 1/4W 144568R24 RES MF 100 OHM 1% 1/4W 144568R25 RES MF 8.25K 1% 1/4W 144549R26 RES MF 8.25K 1% 1/4W 144549R27 RES MF 121K OHM 1% 1/2W 144588R28 RES MF 121K OHM 1% 1/2W 144588R29 RES MF 121K OHM 1% 1/2W 144588R30 RES MF 121K OHM 1% 1/2W 144588R31 RES 698 OHM 1% 1/4W 144511R32 RES 698 OHM 1% 1/4W 144511R33 RES 698 OHM 1% 1/4W 144511R34 RES 698 OHM 1% 1/4W 144511R35 RES MF 2.21M 1% 1/4W 144576R36 RES MF 2.21M 1% 1/4W 144576R37 RES MF 2.21M 1% 1/4W 144576R38 RES MF 2.21M 1% 1/4W 144576R39 RES MF 221K 1% 1/4W 144629R40 RES MF 221K 1% 1/4W 144629R41 RES MF 221K 1% 1/4W 144629R42 RES MF 221K 1% 1/4W 144629R43 RES MF 10K 1% 1/4W 144504R44 RES MF 10K 1% 1/4W 144504R45 RES MF 10K 1% 1/4W 144504R46 RES MF 10K 1% 1/4W 144504R47 RES MO 46.4K 1% 1W 144637R48 RES MO 46.4K 1% 1W 144637R49 RES MO 46.4K 1% 1W 144637R50 RES MO 46.4K 1% 1W 144637R51 RES MF 90.9K 1% 1/4W 144557R52 RES MF 90.9K 1% 1/4W 144557R53 RES MF 1M 1% 1/4W 144577R54 RES MF 1M 1% 1/4W 144577R55 RES MF 1M 1% 1/4W 144577R56 RES MF 1M 1% 1/4W 144577R57 RES MF 200K 1% 1/4W 144531R58 RES MF 200K 1% 1/4W 144531R59 RES MF 200K 1% 1/4W 144531R60 RES MF 200K 1% 1/4W 144531R61 RES MO 100K 5% 2W 144698R62 RES MO 100K 5% 2W 144698R63 RES MO 100K 5% 2W 144698R64 RES MO 100K 5% 2W 144698

R65 RES MO 100K 5% 2W 144698R66 RES MO 100K 5% 2W 144698R67 RES MO 100K 5% 2W 144698R68 RES MO 100K 5% 2W 144698R69 RES WW 220 OHM 10% 5W 139256R70 RES WW 220 OHM 10% 5W 139256R71 RES WW 220 OHM 10% 5W 139256R72 RES WW 220 OHM 10% 5W 139256R73 RES MO 10K 5% 2W 144638R74 RES MO 2.2K 5% 2W 144666R75 RES MO 100K 5% 2W 144698R76 RES MO 100K 5% 2W 144698(F1) HOLDER FUSE 5X20MM PCB MOUNT 178159(F2) HOLDER FUSE 5X20MM PCB MOUNT 178159(F3) HOLDER FUSE 5X20MM PCB MOUNT 178159(F4) HOLDER FUSE 5X20MM PCB MOUNT 178159(V1) SOCKET 9 PIN TUBE CERAMIC 178170(V2) SOCKET 9 PIN TUBE CERAMIC 178170(V3) SOCKET 9 PIN TUBE CERAMIC 178170(V4) SOCKET 9 PIN TUBE CERAMIC 178170(V5) SOCKET 9 PIN TUBE CERAMIC 178170(V6) SOCKET 9 PIN TUBE CERAMIC 178170(V7) SOCKET 9 PIN TUBE CERAMIC 178170(V8) SOCKET OCTAL TUBE CERAMIC 178169(V9) SOCKET OCTAL TUBE CERAMIC 178169(V10) SOCKET OCTAL TUBE CERAMIC 178169(V11) SOCKET OCTAL TUBE CERAMIC 178169

750082 INPUT PCBJ1 JACK PHONO GOLD 117862J2 XLR FEMALE HORIZ PCB WITH LATCH 117814J3 XLR FEMALE HORIZ PCB WITH LATCH 117814J4 CONN 3 POS MALE MTS100 NORMAL 117214J5 CONN 3 POS MALE MTS100 NORMAL 117214J6 CONN MALE 6 POS FRICTION LOCK 117218R1 RES MF 221K 1% 1/4W 144629R2 RES MF 100K 1% 1/4W 144528R3 RES MF 221K 1% 1/4W 144629R4 RES MF 100K 1% 1/4W 144528S1 SWITCH SLIDE DPDT 148076S2 SWITCH SLIDE DPDT 148076

Ref. No. Description Part No. Ref. No. Description Part No.

15 16

EXPLODED VIEW and PARTS LIST

1 005653 CHASSIS2 005650 RCA SPACER3 101197 SCREW HI/LO 4-24 X 3/8 PH RD BLK4 404007 WASHER LOCK 6 X .288 INT STAR5 104165 WASHER 3/8 INTERNAL TOOTH GOLD6 402003 NUT KEP 6-327 750082 ASSY INPUT PCB8 084219 POST BINDING DUAL 4MM THREAD9 404198 LOCK WASHER10 410015 NUT M4 INT STAR SS12 171729 CABLE ASSY POWER SWITCH13 104165 WASHER 3/8 INT TOOTH GOLD

19 400157 SCREW MACH 6-32 X 1/4 PH PN20 114012 BALL STUD21 165065 TUBE 12AX7A McINTOSH22 165067 TUBE 12AT723 165070 TUBE KT88 WITH McINTOSH LOGO24 017761 AIR PIPE25 400292 SCREW MACH 6-32 X 3/8 PH FH BLK26 750085 POTTED TRANSFORMER OUTPUT27 750086 POTTED TRANSFORMER POWER28 166126 DECAL OUTPUT TRANSFORMER29 166127 DECAL POWER TRANSFORMER30 005651 TUBE COVER

31 017862 PUSH-ON FOOT32 125667 NAMEPLATE33 106012 SPRING CLIP: PUSH-ON35 017452 KLIP WIRE36 178161 HOLDER FUSE 5 X 20mm IEC37 404016 WASHER INT STAR .5 X .630 X .02238 102006 NUT MACH 10-32 W/LOCK39 078024 GROMMET RUBBER 1” ID40 078025 GROMMET RUBBER 3/4” ID41 017859 SPACER NYLON 6-32 X 7/1642 117487 RECEPTACLE AC LINE43 074091 TERMINAL BLOCK AC

Ref. No. DescriptionPart No.

44 404001 WASHER FLAT STEEL 4 X 9/32 X .02545 402022 NUT MACH 4-40 X 3/16 X 1/1646 122379 CHOKE FILTER47 402005 NUT MACH 8-32 W/LOCK48 005425 SUPPORT BRACKET49 750675 ASSY AMPLIFIER PCB50 005426 BOTTOM COVER51 401078 SCREW TAP 8-32 X 5/16 PH PN BLK52 017542 PLASTIC FOOT53 400153 SCREW MACH 8-32 X 1/2 PH PN54 401109 SCREW TT 6-32 X 5/16 PH PN BLK

MC275

REPACKING INSTRUCTIONS

17

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 thewithin schematic material, which is intended for information only.

McINTOSH LABORATORY, INC., 2 CHAMBERS STREET, BINGHAMTON, NEW YORK 13903 Printed in U.S.A. Part Number 041046

STEREO POWER AMPLIFIER

SERVICE MANUALSTARTING WITH SERIAL NO. WV1536

MC275