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MC 250
SERVICE INFORMATION
STARTING
MCINTOSH LABORATORY INC. 2 CHAMBERS STREET BINGHAMTON, NEW YORK
WITH
SERIAL
NO.
23L48
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MC 250
ELECTRICAL SPECIFICATIONS
Power Output:
100 watts RMS continuous, 50 watts per channel operating
simultaneously, into 4 ohm, 8 ohm, or 16 ohm loads.
Harmonic Distortion:
Less than 0.25% at rated power output from 20Hz to 20,000Hz.
Intermodulation Distortion:
Less than 0.25% for any combination of frequencies between
20 Hz and 20,000 Hz.
Frequency Range:
At rated output both channels: +0 to -0.25dB from 20Hz
through 20,000Hz.
Output Damping Factor:
Greater than 10 for any output tap.
Input Sensitivity & Impedance:
Input sensitivity is 0.5 volts. Input impedance Is 200K ohms.
Hum & Noise :
Greater than 90dB below rated output.
Power Requirements:
117 volts AC,50-60Hz, 50 watts at zero signal output, 250
watts at rated output.
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MC 250
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MC 250
LEFT
CHANNEL
POWER
OUTPUT PRINTED CIRCUIT BOARD
043-916
RIGHT CHANNEL
POWER
INPUT
SECTION
OUTPUT PRINTED CIRCUIT BOARD
PRINTED
CIRCUIT
BOARD
043-795
043-916
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MC 250
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MC 250
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SCHEMATIC NOTES
1. Unless otherwise specified: Resistance values are in ohms, 1/2 watt, and
10% tolerance; capacitance values smaller than 1 are in microfarads (µF);
capacitance values greater than 1 are in picofarads (pF); inductors are in
mi c rohen r i es (µH).
2. Printed circuit board components are outlined on the schematics by dotted
lines. The circled numbers on the dotted lines correspond to the numbers
on the PC Board layouts.
3. The heavy lines on the schematics denote the primary signal path.
4. All voltages indicated on the schematics are measured under the following
conditions :
a. Use of an 11 megohm impedance VTVM.
b. All voltages ±10% with respect to chassis ground.
c. No signal at input terminals.
d. AC input at 117 volts, 50/60Hz.
e. Front panel controls at:
MC 250
5. In units with Serial No.'s below 28L21: R88, R89, R90 & R91 are used;
6. In units with Serial No.'s from 28L60 to 37L75, C5 & C6 are 180pF.
Q21 Q25
BOTTOM TOP
Left Gain
Right Gain
Mode
Fully CCW
Fully
CCW
Stereo
R49 & R50 are 2200W; R86 & R87 are 160W; and R33 & R34 are 33k.
Q19 Q23
BOTTOM TOP
Q26
TOP
Q22
BOTTOM
Q24
TOP
Q20
BOTTOM
LOCATION OF TRANSISTORS NOT ON PRINTED CIRCUIT BOARDS
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MC 250
REPLACEMENT PARTS
All parts not listed are common items
able from radio parts jobbers .
Rep1acement parts may be obtained when
by PART NUMBER from:
Mclntosh Laboratory Inc.
Customer Service Department
2 Chambers Street
Binghamton, New York 13903
(telephone 607 723-3512)
CAPACITORS
Symbol
Number
Cl1 , 12
C27,28
C29
C47,48
C51 ,52
C53,54
C55,56
C57
D1 ,2
D5,6
07,8
D13,14
D15,16
D18
D20
D25,26
D27,28
D31 ,32
Elect.
Elect.
Elect.
Mylar
Elect.
Elect.
Elect.
Elect.
Description
470µF 4V
9300µF 45V
80/80/1 50/50µF
200/200/150/150V
.47µF
100µF 15V
10µF
640µF 25V
500µF 50V
DIODES
reference diode
si.
rectifier diode
rectifier diode
Si .
Si .
rectifier diode
rectifier diode
Si .
rectifier diode
Si .
rectifier diode
Si .
rectifier diode
Si
.
rectifier diode
Si .
rectifier diode
25V
obtain-
ordered
Part
Number
066-136
066-106
066-095
064-045
066-127
066-005
066-157
066-137
070-046
070-022
070-022
070-O4
070-041
070-031
070-031
070-031
070-031
070-022
Q23,24
Q25,26
Rl
R2
R43,44
R57,58
R59,60
S1 ,2
S3
Tl
T2
T3
Si. NPN transistor 132-070
Si. NPN transistor 132-070
POTENTIOMETERS
Left gain 134-206
Right/mono gain 134-206
RESISTORS
Wirewound 3.6k 5W 139-065
Wirewound .56W 5W 139-048
Wirewound .33W 5W 139-071
SWITCHES
Thermal cut out 153-007
Modeselector 153-008
TRANSFORMERS
Power transformer 043-605
Output
transformer
Output transformer (left) 043-668
MISCELLANEOUS ITEMS
Plastic feet 017-040
Owners manual 038-287
Gain control knob 090-017
Shipping
AC power cord 170-021
carton
(right)
033-077
043-667
Fl
Q1 ,2
Q3, 4
Q5,6
Q7,8
Q9.10
Q11 ,12
Q15,16
Q17,18
Q19,20
Q21 ,22
SCHEMATIC
2.5A
Si.
Si
.
si.
Si .
Si .
Si.
Si .
Si .
Si.
Si .
PART
FUSES
circuit breaker
TRANSISTORS
NPN transistor
NPN transistor
PNP transistor
PNP transistor
PNP transistor
NPN transistor
NPN transistor
PNP transistor
NPN transistor
PNP transistor
NO.
038-508
088-001
132-054
132-054
132-056
132-056
132-056
132-515
132-021
132-032
132-524
132-530
15C01047S-M1508
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