McIntosh C20 - User manual

C20

STEREOPREAMPLIFIER

(SerialNo.6L700& above)

MAINTENANCE

MANUAL

DESCRIPTION

COMPONENT

NO.

Switch,

Input

Selector

Switch,BassCompensator

Switch,TrebleCompensator

Switch,

High

Frequency

Cutoff

Filter

Switch,RumbleFilter

Switch,ModeSelector

Switch,

TapeCompare

Switch,TapeJack

Switch,Phase

SiliconRectifier,

50PIVat

1.6A

Transformer,

Power

S1,S2

M199A

DESCRIPTION

COMPONENT

NO.

FilterCapacitor,

20/20/40

MFat

300/350/350V

FilterCapacitor,

40/40

MFat

350/350V

Filter

Capacitor,

1000/1000

MFat

15/15V

Control,Bass

Control,Treble

Control,

Loudness(AuralCompensator)

Control,Volume

—4

Section

combined

with

power

on-off

switch

Control,Balance

Control,Bass

Trim

(Lo

Bass)

rearpanel

C102

C103

C104

R7(2

used)

Special

componentsused

intheC20are

listed

below.

These

compo-

nents

are

designed

and

builtspecifically

forthe

C20.They

maybe

pur-

chased

directlyfromCustomerService,MclntoshLaboratoryInc.When

you

Table

SPECIAL

COMPONENTS

(Schematic

No.

SC119-201)

order

parts

sure

give

the

SCHEMATIC

NO.and

DESCRIPTION

from

Table

below,

and

serial

and

model

number

for

youramplifier.

Table1.C20VOLTAGEANDRESISTANCECHART

(SchematicNo.SC117-201)

Tube

12AX7

(V1)

12AX7

(V2)

12AU7

(V3)

12AU7

(V4)

12AX7

(V5)

12AX7

(V6)

12AX7

(V7)

6X4

(V8)

PinNo.

DCVolts

No.Signal

146

1.0

5.6

-5.6

110

1.0

—

146

1.0

5.6

-5.6

110

1,0

2.4

5.6

-5.6

198

120

—

2.4

5,6

-5.6

198

120

—

104

5.6

-5.6

230

104

5.6

-5.6

200

250

5.6

-5.6

250

315AC

—

6.3AC

315AC

335

Resistancein

OhmsUnitOff

130K*

2.2K

360K*

56K

—

130K*

2.2K

360K*

56K

120K*

<50

1.8K

14K*

1.1M

100K

—

120K*

<50

1.8K

14K*

100K

—

330K*

110K

1.8K

222K

22K

—

330K*

110K

1.8K

31K*

222K

22K

—

7K*

47K

7K*

47K

580

—

560

NOTES:1.HighimpedanceVTVMisusedtomeasureoperatingvoltages.

2.Resistancemeasuredtogrid,(chassis)

3.* Denotespin7 ofV8groundedforthistest.

4.Controlpositionsfortestsareasfollows;

MODESELECTOR

BALANCE

PHASE

H.F.FILTER

LOUDNESS

INPUTSELECTOR

BASSCOMPENSATOR

TREBLECOMPENSATOR

BASS

TREBLE

RUMBLEFILTER,

TAPEJACK,

TAPECOMPARE

VOLUME

LOWFREQUENCYTRIM

STEREO

FLAT

TAPEHD2

TAPE

OUT

ON,CCW

C20

Schematic

(Schematic

No.

SC117-201)

NOTES:

(1)

THlS

SCHEMATIC

APPLIES

TOC20

PREAMPLIFIERS

WITH

SERIAL

NUMBERS

6L700

AND

ABOVE.

(2)ALL

ROTARYSWITCHES

ARE

SHOWN

INTHE

EXTREMECOUNTERCLOCKWISE

POSlTION.

(3)ALL

PUSHBUTTON

SWITCHES

ARE

SHOWN

INTHE

"OUT"

POSITION.

(4)

RESISTOR

VALUES

AREIN

OHMS

±10%,

½WATT

EXCEPT

NOTED.

(5)

CONDENSERVALUES

AREINMFDFOR

NUMBERSLESSTHANONE,

ANDIN

MMFD

FOR

NUMBERSGREATERTHANONE.

(6)IN

SOMEUNITS C104

MAYBE

FOUND

ASTWO

SEPARATE

2000

MFD/15V

CONDENSERS.

(7)A

RESISTOR

SOME

UNITS

MAYBE

USED

THIS

POINT

ADJUST

THE

VOLUME

CONTROLS

TRACKING

CHARACTERISTlC.

THE

VALUE

MATCHED

TOTHE

PARTICULARVOLUMECONTROL

USED

THESE

COMPONENTS

HAVE

CLOSETOLERANCE

THEIR

VALUE,

HAVE

SPECIAL

CHARACTERISTICS

SUCH

LOW

NOISE

ORA

SPECIALRESISTANCETAPER.

LABORATORYINC.

2CHAMBERSSTREET,BINGHAMTON,N.Y.

Phone-AreaCode607-723-5491

2M-AA117-2015-62

BE012003

CustomerService

MclntoshLaboratoryInc.

2ChambersStreet

Binghamton,NewYork

Ourtelephonenumberis723-5491.

Thedirectdialareacodeis607.

YourC20willgiveyoumanyyearsofpleasantandsatisfactory

performance.Ifyouhaveanyquestionsconcerningtheoperation

ormaintenanceofthispre-amplifierpleasecontact:

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