Sherwood S-9500B User manual

MODEL
S.95OOb
ALL-SILICON
SOLID.STATE
STEREO
AMPLIFIER
SERVICE
MANUAL
Tone controls for both channels.
Adjustment of the Bass or Treble
control knob will vary the tone of
both channels simultaneouslY.
Serial No's. T704104
TO T704604
Main control for Power on-off and
Loudness of both channel s. Auto-
matically boosts bass at low levels
(if switch below at "Loudness In").
Controls left-to-right
stereo balance.
Stereo head-
phone jack.
Pilot Light
Remote SpeakerSet On-off Switch. Will
disconnect this speaker set when
depressed right.
Main SpeakerSet On-off Switch' Will
disconnect this speaker set when
depressed right.
Selector Switch.
Chooses phono,
tuner, or auxrliary
i
nput
s.
Preamp Level. Controls
preamp
level only.
Tape Monitor Switch'
Normally set to left.
will connect in tape
monitor jacks on rear
if depressed right,
Hi Filter. Depress
right for l2dbloctave
attenuat ion of un-
desired tones such
as tecond "scratch',,
Loudness Compensetion Switch.
Normally set to left, will remove
circuit which boosts bass at low
settings of Loudness control if
depressed right.
MODEL
S.95OObSTEREO
AMPLIFIERSPECIFICATIONS
{<
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INPUTS:6high level (2 tape monitor), 2
(RIAA)
Phono-
preamp.
POWER
OUTPUT: music power: (4O) 80 watts, (8O)
50 watts; continuous power each channel: (4O) 30
watts, (8Ct)
20watts at l.D%odistortion.
OUTPUTS: 4 to 16-ohm left and right spkr. main and
remote; mono speaker, stereo headphone
and record
output.
INVERSE FEEDBACK: 35db.
DAMPING FACTOR: 30:1at 8 ohrrs"
FREQUENCYRESPONSE:
(20w)
20Hzto 20KHz+1 db.
TONE CONTROL RESPONSE: Flat setting, 20Hz to
z0K.llz 11 db.
TONE CONTROLRANGE: 15KHz, 15db. boost or cut
40Hz
20db. boost or cut.
PREAMP. EQUALIZER CURVES: AES/RIAA phono.
SENSITIVITY: Radio - 0.20v Phono - 1.6mv. (PH
Input is adjustable with Preamp Level control).
MAX" INPUT CAPABILITY: Phono: 160mv. for less
than 170
dist. Radio: 2.8v. for less than LVo
dist"
MAX. HUM and NOISE: Vol. control min. , 90db
(weighted) betow rated output. Tuner input (controls
max"), 80db. (weighted)below rated output. Phono
input (controls flat), 60db. below rated output.
INTERCHANNEL CROSSTALK: Less than -45db" at
1KHz"
POWER CONSUMPTION:115-125v, 6QHz;10to L20
watts fused.
TRANSISTOR
COMPLEMENT: 22 silicon transistors,
2 silicon rectifiers.
SIZE: 14x L0-l/2 x 4 in" high.
SHIPPINGWEIGHT: 22 lbs"
*All specifications takenwith 120Vline.

SWITCHED
AC
RECEPTACLE
LEFTCH.
BIAS
ADJ. Ixl tr
x2
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LEFT CH.
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QilO
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F2 -2AnP F3.zAMP
FUSE
STEREO.MONO
swrTcH tHl
FILTER
cAUTTON
! USE
STANDARo
lll2 AMPFUSE.
DO
NOTUSE
StO-BLq(2AMP
FOR
SPKR.
FUSES)
Ft
- | l/zalP
SELECTOR
swtTcH
PHONO
TUNER
AUX. APEMONITOR
PWR OFF
SPEAI(ERS
ttnlloJti
All power fuses on export models using 230Vfor power, will requite 50Vo
less current
rating than the comparable domestic unit. Voltage rating will remain the same.
COIITIIECTTURNTABLE OR CHANGER
GROUNO
LEAD HERE.
ONNECT
OI{LY
TO
-dbru.
oR,crr uErr Rtc"r uErro
{o
o
to
Qo
o o
or
Ho
o o
oE
OO
RIGHTSPKR.
+@@
MAIN
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+
+
LEFT SPKR
@-^,P
REI'OTE
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ll5-125V
6OHr
SPKR FUSES
Page3

STRYICING
YOTTAGT
CHECKS
Preliminary checks of the D.
C. voltages present at
various points in theS-9500b
can prove useful in 1o-
cating defective components. They are inconclusive,
however, in determining if transistors are operating
properly in all aspects. They canonly indicate wheth
-er the transistor is open, shorted or functioning, 4!
howwell the transistor is functioning.
IN GENERAL:
Correct voltages
indicate a functioningtransistor.
The same voltage at the collector and emitter
indicates a shorted transistor.
Full supplyvoltageon the collector andnovoltage
on the emitter indieates anopentransistor.
OUTPUT
TRANSISIOR
BIAS
Of alt the specifications
which require checkingto as-
certain correet performance of the S-9500b,
proper
output transistor operation is the most important and
critical. Adjustment of the output transistor bias is
necessary if output transistors are replaced*, or the
amplifier exhibits one or more of the following symp-
toms:
1. Overheatingof the output transistors under nor-
mal operating conditions.
2. Excessive low level Intermodulation Distortion-
more than 0,5Vo
at 2.0 volts across 8 ohms (0.8
watts, IM power).
Adjustment of outputtransistor bias should then pro-
ceedas follows:
Connect
D.C. voltmeter of at least 370
knownac-
curacy to transistor sideof appropriatechannel's
outputterminals.
Turn arnp. on and adjust output balance
pot for
that channelso that approx. L/28+ voltage is on
the outputcapacitor"
Connect
an Intermodulation Distortion analyzerto
to the amplifier TP. MON. (aux.) input , turn
volumn control to ma:<imum
and adjust the ana-
lyzer output for an amplifier output of.
2.0Vacross
I ohms. (Because the output stages have been
set into heavy class "8" operation by the "pre-
setting" in Step2, a elass "8" notch in the dis-
tortion waveform will be obvious.
) NOTE: When
adjusting bias for class "A8", adjust until class
"8" notchis almost eliminated. Class "A" begins
beyond this point, and notch shifts to right.
Inerease analyzer output until clipping can be
observed. Fine adjust outputbalance
pot so that
clipping is symmetrical"
3.
a.
6.
IMPORTANT: Misadjustment of the bias pot car.
causeheavyclass "A" operationof the outputtransis-
tors, causingthem to overheat.
The followingperformance indicates a properly oper-
ating output stage with 8 ohm load.
-Less than0.57oIM
distortion at 2.0V"
-Typically 0. goIM distortion at t0 Volts.
-18 watts of power per channelat clipping"
1" Turn amplifier off.
2. Set output balance pots (left and right channels)
to mechanical center andbias pots fully counter-
clockwise.
{<ft is extremely important that themiea insulating wishers used to separatetheoutput transistors fro
be unbrokenandinstilled properly with silicon grease liberally appliedto all surfaces in contar
Make certain the emitter and
basepins of the output transistors do not contact any part of the he
NOTE: Refer to speakerload connectionson schematic, being careful to observe
ground-connections.
Page4
cL-Ass
"B' CLASSH

SERVICING
1. AMPLIFIER/PREAMP STAGEISOLATION: Eval-
uat thus,
B+ supply shouldbe suspectedfor malfunction. If one
channel
only, evaluatewith test signal whether signal
feedsproperly through phonopreamp, auxiliary high-
level input, or into volume control at high side (this
isolates power amplifier section from tone amplifier
section).
2. FAULT ISOLATED TO POWERAMPLIFIER: With
DC upply
voltages, colleetor, emitter, ild base voltages of
transistors on the driver-circuit boards andof output
transistors in the faulty power amplifier channel. The
voltages shouldbe verified against those
shown
on the
schematicfor 120V
power line andalso against those
in the 2nd
channel
(assumedto beoperating
comectly).
Note that output electrolytic coupling capacitor DC
voltage (on transistor feed side) shouldread approx.
L/2 of.
g+ supply voltage. Note in most cases of a
defective driver or output transistor, the fuse will
open and prevent the taking of a usable center-point
voltagereading. Therefore, it is valuable to operate
the amplifier with a variable voltage power line
(Variac) equipped
with a line wattmeter (or ammeter)
to identify abnormal power consumption.
With the Variac, reduce thepowerlinevoltage tozero,
replace fuse, and slowly increase power line voltage
upwardwhile observing wattmeter. (The power con-
sumption should
not exceed10-15 watts as the
voltage
is increasedup to rated 120volts. If powerconsump-
tion reading beginsto exceed 15watts, starting from
zero voltage, do not increase power line voltage fur-
ther. ) Nowverify center-point voltagefor half-voltage
reading.
If center-point voltage reads extremely low, suspect
defective output or driver transistors on low side
(schematic shows these as bottom devices in each
channel). lf center-point voltage reads extremely
hrgh, suspect defective high-side output or driver
transistors.
Remove both driver transistors from their sockets.
If power consumption
drops considerabll', thenfaulty
driver transistors shouldbe suspected. If powercon-
sumption remains unusually high, then faulty output
transistors should
be suspected. If not, suspect
pre-
driver or bias-regulator transistor or assoeiated
components.
H afl above
seemsnot to be at fault, then verify that
output couplingelectrolytic capacitor is not shorted,
other
capacitors
arenot
shorted,circuit board
contains
no solder or etchingshorts, openresistors, or poor
solder connections. (Note: a small error voltage
at pre-driver base and/or emitter will disruptgrossly
the operation of the driver andoutput transistors. )
If center-point voltagereads approximately l/2 voltage
in accordancewith above
check, apply audio signal to
channel being investigated and measure distortion as
per service instruction manual. Distortion which
exceeds
amplifier ratings might be due to oneof the
following:
1. Outputtransistors do not havematchedbeta"
2. Outputbias requires readjustment.
3. Driver transistor has low beta.
3. FAULT ISOLATED TO TONE CONTROL
A collec-
6r, ernlii6, ild base on tone circuit board and
compare with schematic andwith good channel. Feed
1KC audio signal to input connection to tone circuit
board. Compare outpuf voltage to input voltage which
should have a gain ratio of about 6db (2X).
Isolate inoperate stage by checking signal at input of
treble control. Compare this voltage to input voltage
which should rezult in lst stage gain - approximately
6db(2x)"
Evaluatedistortion in conjunctionwith power amplifier.
Verify bass and treble frequency responsewith bass
and treble boost andcut characteristic curves shown
in service manual.on
Page
8.
4. FAULT ISOLATED
TOPREAMP: Check
DC
voltages
at t d base
onpreamp.
circuit board and compaJ'e
with schematic and with
good channel. Feed 1KC audib signal to phono input
jack. Compare outputvoltage at input of tone circuit
board to input voltage. The resulting calculated gain
ratio should beapproximately40db
(100X)
withpreamp.
gain (phono
level) control at maximum gain. Isolate
the inoperative stage by checking signal voltage at
collectorof 1st stage. Verify frequency
responsewith
phonoand tape equalization curves shown in service
manual on PageB.
5. FAULT ISOLATED
TOPOWERSUPPLY:
CheckDC
vol er capaci-
tor sections andcompare
with thoseshown
oh schema-
tic. If a voltage measures low, remove leads to
amplifier or receiver loads to isolate possibility of
Ieakyor shortedelectrolyticcapacitor section. Page
5

PARTS LIST
TRANSISTORS
(All are silicon) PART NO" PRICE
Audio, Low signal-no
dot (Hi beta), (Q101,105, 20L, 205)
Audio, Low signal-Green dot (Low Noise), (Q102, 202)
Audio, Low signal -no dot (Hi beta), (Q103, 104, 107,2A3,204,207)
Pre-Driver, NPN (Q106,
206)
Driver, NPN, (Q108,208)
Driver, PNP, (Q109, 209)
Output,
NPN, (Q110,
111, 210,211)
2N3900
s22004
sPs41
2N3900N
s22004N
SPS41N
s22004
SPS41
16E1330
40361F
S43?F
s353
$1.04
0.63
0.81
L"t4
0.73
0.91
0.63
0.81
L.26
2.92
3.36
2.84
you will notethat all transistors usedin the S-?800are color-coded with a dot or mark of some
co
located on the top of their case. (Sometransistors have no mark, but this also is identification" )
replacement transistors, it is imperative that you indicate not only its part no",but the color dot o
noOy: red, yellow, none, (1, -2-,- or -3). This is particularly important when replacing out;
DESCRIPTION PART NO. PRICE
1500pf, 45V
(C190,
290)
2500pf., 80V (342)
0.5pf, 50V(C170, L12, 210, 272')
Sttf
, 5V (C136, 236)
5pf, 20V, (C143, 2431
Ittf, 25V, (C111
, L32, ztL, 232)
201tf, 5V (C160, 260)
100pf, 3V (C100,t02, 200, 203)
Ittf, 15V
(C150,
250)
201tf.,50V (C171, 271')
500pf, 50V(C343,344)
500prf,
25V (C345)
Insulator, Thermo-Film, (T03)
tr\rse, 2 AMP, 3AG (F2, 3)
Fr\rse,t-t/z AMP, 3AG(F1)
Knobs, Medium (Vindicator)
Knob, Small Plastic, Unmar'lsed,Phono Level
Light Bulb, Pilot #53
Control, 50K ohm hd, w/AC Sw. (R150A,
B, s4)
Control, Bass, lM ohm D'ual
(R134A,
B)
Control, Treble, 250Kohm Duat (R140A,
B)
Control, Balance, 100K
ohm (R153)
Control, PhonoLevel, 1.5K ohm (R120A,
B)
Pot., P.C., 500ohm Bias (R184, 284)
Pot. , P.C. , 250Kohm OutputBal" (R1?0, 270)
Rectifier, Silicon (X1,
2)
Socket, Driver Transistor
Socket, Output Transistor
Stereo Headphone
Jack
Fuse Post
Switch, Selector, 3 Pos. (S1A,
B)
Switch, Function, 5 Pos. (S2)
Switch, Rocker, (Non-shorting), DPDT (S3AB)
Switch, Rocker, (Shctrting)
DPDT, (SrtA;
5A,
B;6^A,
B;7A, B;8A,B)
Transformer, Power, 60Hz Domestic (T1)
Transformer, Power, 50-60Hz Export (T1)
At20T7 -2
A.120T11
8120X3
8120X4
8120X6
8120X7
8120X12
B120x24
8120X?5
8120814
8120830
8120831
A021Rl-0
312002.
31201.5
B,467X4
4604B5
630853
A6?1T1-6
A670T5
-3
A6?0T6-3
A6?0T7-3
4670T11-1
^A675T1-0A
A675T9-0A
A692T3
-0
A?90T4M-1
A790T7-0
A795L1-0
A?96X2
-1.A
A860T6-0
A860K5
-3
A864T22
-5
A864T23-5
8922T2-5C
28922T2-5CX
$2.70
3.80
0.59
0.63
0.59
0.59
0.63
0.53
0.59
0.36
1.48
0.99
0.05
0.15
0.15
2.43
0.15
0.15
4.28
2.84
2.84
1.04
1.89
0.90
0.45
L.26
0.23
0.18
1.08
0.95
3.47
2.25
0.86
0.86
1?.10
32.85
Page 6

FREQUENCY
lN
Hz
20 50 tOO 2OO 5OO lx 2x 5x lox 2Ox 5Ox l00x
0
v,
J
ul -5
g
.: -r0
E
o_t5
POWER
AIiPLIFIER
RESPONSE
tl
AUDIO RANGE
rl
fow at
-N \
,llF
rorc 50u^aaw^va
\
\\
20w
frlcucfacY lx HEtlz
tO lO0 2OO 5OO rr
tor{c coNrrot araD
FrtTCr cH^tactEitsrtcs
OUTPUT I'T WAVTS (?EAT}
lll1610a0
z
o
Ft
c
o
c
o
ul
2
o
a
3
II
E
laa
OUT'UT IN trolo
watTt (ir.rs I
Cont inuous
Power Output
vs.Distortion
4&8 Ohms
(recr cxrxx:r)
8
)xt{
\4l
txr{ -t
I
CLEANING ESCUTCHEON FACE PLATE: The beige es-
cutcheon on your Sherwood equipment has been finished
with a durable baked enalnel. Toclean, wipe with a chamois
or cloth dampenedwith a water solution of liquid detergent.
Do not use an abrasive scouring powder.
EXPORT MODELSARE AVAII"ABLE WITH SPECIAL TRANSFORMERS
FOR 50-60 CYCLE POWEI
24OV
AND ARE I\IIARKEDTHUSON THE REAR OF THE CHASSIS.THESE SPECIAL MODELS HAV
TREATED WITH FUNGICIDE AND ANTI-CORONA IVIATERIALSFOR ADDED PROTECTION IN HU
ETECTRONIC
TABORATOR
tES,
lNC.
I RVI
NG 8-7300
€
rO
rn
=
=
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J
4300
Page 8 NORTH cALIFoRNIA AVENUE, CHICAGO,
ILLINOIS60618

REC.
MON.
PHONO
AUX
TUNER
REC.
MON.
Ptf
oNo
AUX
TUT{ER
LEFT CHANNEL
RIGHTCHANNEL
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AMPLIFIER
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FORRA'ED
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I9OTY
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ALTERI{ATE
PR|rARY CIRCUITS
FOR EXPORT
IIOO€LS
SHERWOODS-95OOb
80 WATTSTEREO
AMPLIFIER
SERIAL
NO.T704tO4 TO T704604
st53
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CHAililET,tA|l{
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IIOTE:
l1!: ALLREsrsrons aREr/a wArr oRL€ss,trooa
!99t( rolenlrce uflLEssorHERwtsE
SPECIFIEIL
ALL FRACTIONAL
VALUE
CAPACITORS
AREll{ rl. OTHER
CAPACITORSEXCEPTELECTROLYTICS
sTEREO AiE tr Pr. COl{ilECT
E^L^rcc ,I3rl"
RIGHT CHAIT{EL:
OOXFOiIEiIT
SYIBOLS ARE TH€SAIIE A8
THE LEFTCHAiIflEL ASOVEEXC€PT FOR
Ailll{ci€tsE lx NuIBEill{o BY
olE Huil0nE0. s78
RIGHT f Altr
CHAI{NEL
AUOIO ORIVER EOARD
AO3lTt8
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2 AfP
STEREO
HEADPI{OIIE8
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