Eico ST 40 User manual

EICO

eicoETZTI
40 WATT INTEGRATED STEREO AMPLIFIER
GENERAL DESCRIPTION
The E1CO Model ST-40 is acomplete high fidelity
stereophonic control centeranda pair of 20-watt amp-
lifiers, all on one chassis* With It, you can select,
preamplify, and control any stereophonic or monophic
source and feed it through the self-contained dual 20
watt amplifiers to astereo pair of speaker systems.
Provision Is made for operating acenter speakerdirect-
ly from the ST-40*
FEATURES
1. Provision for two stereo phono cartridges to be
connected. Permits the use of both aturntable and a
record changer in the installation. One pair presents
47KQ load and the other pair 100KQ load, to cover
most popular cartriges* RIAA equalization.
2. Provision for connecting stereo tape heads* NARTB
equalization for 71/2 Ips*
3. High level input pairs for multiplex adaptor, pre-
amplified and equalized tape, FM tuner, and AM tuner,
4* Separate level and balance controls* Null-type
balance checking circuit.
5.
Switched high and low frequency filter circuits
permit elimination of rumble problem or scratch and
distorrion when need be.
6. Switched loudness compensation*
7. Tape monitor switch*
8. Feedback equalization, with feedback around both
preamplifier stages. High overload point.
9* Bass and treble tone controls are of the variable
inflection point, feedback type for exceptionally low
distortion and the most desirable control characteristics.
These controls do not affect the volume or interact with
each other, and boost or cut at the extremes of the
audio range do not affect the mid-range.
10. Separate filament windings and hum balance con-
trols for each channel permit an optimum hum balance
for each channel, rather than acompromise for both
channels.
11. Unused inputs grounded by SELECTOR switch to
eliminate cross-talk —except for TAPE inputs, since
some tape machines are adversely affected if playback
outputs are grounded during recording.
12. Provision for feeding acenter speaker directly
from the ST-40.
13. Conservatively operated 7591 output tubes, and
highly efficient *GZ34 rectifier.
COPYRIGHT© I960 ELECTRONIC INSTRUMENT COMPANY, Inc.

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SPECIFICATIONS
POWER OUTPUT: 40wattsfotal; 20 watts each chan-
nel continuous sine wave power
IM DISTORTION (60 &7000 CPS at 4:1): 1% at 20W
each channel; 0-6% at 10W; 0- 16% at 1W
HARMONIC DISTORTION: Less than 1% 40-20, 000
cps within Idb of 20 watts each channel; less than
1*5% 30-20,000 cps at half-power each channel
FREQUENCY RESPONSE: ±0. 5db 40-20, 000 cps at
20 watts each channel, ±1 db 12-25, OOOcps at 1watt
each channel
INPUT SENSITIVITY INPUT IMPEDANCE
Phono A3Mv 100KQ
Phono B3Mv 47Kfi
Tape Head 1. 75Mv 1MQ
FM 360Mv 500KQ
AM 360Mv 500KC5
Multiplex 360Mv 500KQ
Tape 360Mv 500KQ
TONE CONTROL RANGE: ±15db at 50 cps and lOkc
DAMPING FACTOR: 11
SPEAKER CONNECTIONS: 4, 8, !6£2
TAPE OUTPUT IMPEDANCE: 400fiat20kc when using
low level inputs; same as the output impedance of the
source when using high level inputs
TUBES: 2-12AX7, 4-12DW7, 4-7591, 1-GZ34 recti-
fier
POWER SOURCE: .117V, 60 cps
POWER CONSUMPTION: 165 watts
CONVENIENCE OUTLETS: 1controlled by power
switch, 1not switched
FUSE: 3amperes
SIZE (HWD): 51/8“ x15 7/8 x13 1/8“
CABINET INSTALLATION
GENERAL
1. Mount horizontally on awell-braced shelf. The
stock thickness of the wood.pane Imay not exceed 3/4"„
2* Do not remove feet for mounting* Air must be
allowed to enter through the perforations in the bottom
plate to avoid overheating.
3* Any shelf above the unit must be spaced away at
least 3inches^ Allow at least a11/2" tolerance on
each side of the unit.
4, Leave the back of the cabinet entirely open*
PREPARATION OF UNIT
1* Turn unit over and loosen the front and rear pairs
of screws (4 in all) that fasten the bottom plate to the
side pieces. Remove the center pair entirely. Then
turn the unit back right side up.
2. Remove the 6screws, one on each side, that fasten
the cover to the side pieces* Remove the cover and
set aside*
3. On the top side of the chassis, loosen all 6screws
(3 on each side) that fasten the chassis to the side
pieces*
4. Push both side pieces back as far as they will go.
The screws that have been loosened will move from
the front to the rear ends of the slots in the chassis and
the bottom plate* Then re-tighten all the screws that
have been loosened* Check to see that all the tubes
are properly seated in their sockets and then replace
and re-fasten the cover to the side extrusions.
5. Detach all the knobs from the control shafts and
then remove the 4screws, (2 previously concealed by
knobs and 2in the recessed grea) that fasten the panel
to the chassis. Lift the panel out over the control shafts
and set it aside. The unit Is now prepared for cabinet
installation.
WEIGHT: 32 lbs.

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PREPARATION OF THE CABINET
1* Two templates are provided, one for the cabinet
shelf and the other for the cabinet panel* The shelf
template is used to locate exactly two holes that are
to be drilled in the shelf* The panel template is used
to locate exactly the required rectangular cut-out. The
two templates must be used together as indicated, as
there is an exact relationship between the locations
of the shelf holes and panel cut-out.
2. To use the shelf template, cut it or fold it back
exactly along the dashed line that corresponds to the
panelthickness* Remove the shelf from the cabinet
and line up this dashed line on the template with the
front edge of the shelf, positioning it also along the
edge to leave at least 11/2" clearance on each side*
Tape the template in position and use a center punch
to mark the centers of the two holes to be drilled* [f
the shelf can not be removed, place the template in a
similar manner on the top side of the shelf if there is
room to drill from the top side, or on the under side of
shelf if there is only room to drill from the under side.
If the template is used on the underside of the shelf,
mark the rear edge of the shelf at the points where the
extended heavy lines on the template hit the rear shelf
edge. After the holes are center-punched, remove the
template and drill carefully through the punched cen-
ters to adiameter of 1/4". If the shelf has been re-
moved for the drilling operation, now re-mount It.
Finally, replace the shelf-template in exactly its former
position on the top-side of the shelf and tape it down*
If the shelf template had been used on the underside of
astationary shelf, now place it on the top-side of the
shelf using the marks on the rear edge of the shelf pre-
viously made. (In the latter case, accuracy may be
improved by cutting the two holes out of the shelf-
template with arazor blade and then lining up the
holes in the shelf template with the holes in the shelf).
3. To use the panel template, cut it or fold It back
exactly along the dashed line. This dashed line cor-
responds to the junction of the top side of the cabinet
shelf and the interior side of the wood panel* Position
the panel template against the interior side of the wood
pane! so that the dashed line rests against the shelf and
the two heavy vertical lines in the panel template meet
with the two heavy horizontal lines in the shelf tem-
plates. Tape the panel template down and use acenter-
punch to make the centers of the four 3/8" holes in the
four corners of the rectangular cut-out shown on the
template. Now remove both templates and drill care-
fully through each of the four punched centers to a
PAGE 3
hole diameter of 3/8". On the front side of the wood
p'anel scribe arectangle externally tangential to the
four drilled holes* Check the height and width of the
rectangle against the panel template dimensions* These
dimensions should not be exceeded* Now carefully
cut out the rectangle with a sabre saw, using asmall-
blade to start accurately in the 3/8" holes. After the
cutting operation, any rough spots or excess material
along the edges of the cut-out may be removed with a
file* Finally, brush or blow out all chips and sawdust.
MOUNTING THE UNIT
1. Insert the unit from the rear of the cabinet, care-
fully guiding the controls through the panel cut-out.
Center the unit Inthe cut-out and re-mount the panel
with the four screws previously removed.
2. From the rear of the cabinet, pull the amplifier
toward you gently, until the front panel is flush against
the wood panel.
3. Now place 5/8" flat washers against the heads of
the two *8 x13/4" screws provided and insert them
from the bottom side of the shelf into the two holes
drilled previously. It may be necessary to shift the unit
slightly to the left or right in order to afford clear ac-
cess for the screws. When both screws have caught,
tighten them to secure the unit to the shelf*
4. Replace the knobs previously removed on the con-
trol shafts.
INPUT CONNECTIONS
Channel 1has 7inputs and channel 2 has 6inputs,
one of which there is no use for at -the present time
(AM 2).*
The channel 1inputs are identified by the suffix
"I" and are as follows:
CH* ILow Level Inputs
PHONO A1
PHONO B1.
TAPE HEAD 1
#:
CH. 1High Level Inputs
FM 1
AM 1
Multiplex 1
TAPE 1
The channel 2inputs*, are identified by the suffice "2"
and are as follows^

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CH.2 Low Level Inputs
PHONO A2
PHONO B2
TAPE HEAD 2
CH.2 High Level inputs
AM 2* (See note)
Multiplex 2
TAPE 2
All high level inputs provide the same gain and flat
frequency response.. Low level inputs provide much
higher gain and the prescribed gain-frequency char-
acteristics of R1AA for phono and NARTB for tape head*
Monophonic sources, such as FM tuner, AM tuner, or
monophonic phono cartridge, are plugged into Channel
1inputs* Stereophonic sources, such as stereo phono
cartridge, stereo tape heads, or FM, Multiplex (MX)
adaptor, are plugged in as follows: left channel Into
channel 1Inputs; right channel into channel 2inputs*
*(npuf AM 2is provided against the possibility of AM-
AM stereo* AM 1is the normal AM tuner input*
Setting the SELECT OR switch to FM-AM and the MODE
switch to STEREO or REVERSE takes care of feeding
two normally monophonic channel 1inputs (FM tuner
and AM tuner) one to channel 1and the other to chan-
nel 2for FM-AM simulcast stereo*
PHONO
The PH. Ainput jacks 1&2and the PH. BInput jacks
1&2permit the use of two magnetic cartridges in your
system. One cartridge can be astereo type and the
other monophonic or both can be stereo. One cartridge
can be in aturntable, and the other in arecord changer
or an inexpensive phono for children's use. Amono-
phonic cartridge is plugged into the channel 1input
only*
When playing amonophonic recordwitha stereo cart-
ridge, set the MODE switch to the MONO 1-2 posi-
tion, specifically intended for this purpose. In the
MONO 1-2 position, the channel 1and 2Inputs are
fully blended internally, and the blend is fed to both
amplifiers. The purpose here Is to cancel extraneous
vertical noise components in the cartridge output*
When playing amonophonic recordwitha monophonic
cartridge, set the MODE switch to MONO 1, the
normal monophonic position at which th^ channel 1
input is fed to both amplifiers*
»
The load presented to the cartridge by the PHONO A
inputs is lOOKCi* The load presented to the cartridge
by the PHONO Binputs is47KQ. The choice of load
impedance permits accomodation of most popular cart-
ridges* Most popular cartridges, including all Shure
and the Pickering 381A require 47KQ load. The Picker-
ing 380A, however, requires 100KQ load.
If the Weathers C501-D cartridge is used, connect a
180KQ resistor in series fol lowed by a33KQ resistor in
shunt, to each output. Plug into PHONO Ainputs*
This network avoids overloading the preamplifier inputs.
^TAPE HEAD
The TAPE HEAD 1&TAPE HEAD 2input jacks permit
the connection of atape deck having no playback
preamplifiers to the unit* The tape head should be of
the conventional high impedance, high output type
normally supplied in decks without playback electron-
ics. if the head is of the stereo type, connect the
upper track output to TAPE HEAD 1and the lower
track output to TAPE HEAD 2,If the head Is of the
monophonic type, connect the output to TAPE HEAD 1.
The load presented to the tape head by each input Is
1megohm.
FM TUNER
The FM 1input jack is for connection of an FM tuner.
AM TUNER
The AM 1input jack is for connection of an AM tuner.
Do not use AM 2for this purpose,
FM MULTIPLEX ADAPTOR
The MX land MX 2Input jacks permit the connection
of an FM Multiplex adaptor* Anyadaptor will provide
aleft channel output anda right channel output. The
left channel output is connected to MX 1and the right
channel output to MX 2.
,/TAPE
The TAPE 1and TAPE 2input jacks permits the con-
nection of atape machine complete with playback
preamplifiers. If the machine provides stereo play-
back, connect the upper track output to TAPE 1, and
the lower track output to TAPE 2. If the machine is
of the monophonic type, connect the output to TAPE 1,

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OUTPUT CONNECTIONS
TAPE RECORDER
The TAPE OUT l&TAPE OUT 2iacks are Intended
for feeding signals out to the "line" recording inputs
of atape recorder. These are Independent outpi sfor
channel 1and channel 2, respectively. They are un-
affected by the LEVEL, BALANCE, BASS, TREBLE,
HI FILTER, and LO FILTER controls.
SPEAKER CONNECTIONS
WARNING: Do notoperatetheamplifierwithout first
connecting speakers to the speaker connection termi-
nals, exactly as described below.
Every speaker has arated impedance, which may be
16, 8, or 4ohms. For an amplifier to provide rated
power output with rated distortion, the speaker used
with it must be connected to the output transformer tap
corresponding to its impedance.
On the rear apron of the unit, there are three 4-con-
nection Terminal Boards (TB). Silk-screened on the
apron is adiagram for connecting upto three speakers;
one each for channels land 2, and an. optional center
channel speaker.
To agree with the established conventions of stereo,
connect the left speaker to the channel 1output, and
the right speaker to the Channel 2output, after read-
ing the connection information below.
The boardat the left, TB1, carries the impedance taps
for channel 1. The board at the lower right, TB3,
carries the impedance taps for channel 2.
SPEAKER TERMINALS FIG. I
PAGE 5
The left board, TB1, carrying the channel 1impedance
taos (16, 8,4£)1. also includes the common terminal
('..< for channel 1. The channel 1speaker is connected
to this common terminal Cand the appropriate channel
1imp, dan se tap, as shown.
The lower right board, TB3, carrying the channel 2
impedancetaps(16,8,4Q), does not carry the common -
terminal Cfor channel 2, in fact, the channel 2
speaker Is npt to be directly connected to this board
atall. The upper right board, TB2, provides the con-
nection terminals for the channel 2speaker. As the
diagram shows, the channel 2speaker is to be connect-
ed between the right-hand pair of terminals on board
TB2. Note that the terminal at the extreme right Is
marked “C", thisbeingthe common terminal for chan-
nel 2.
To complete the connection of the channel 2speaker,
Tjumper wire must be connected between the third
terminal from the right on the upper right board, TB2,
and the appropriate impedance tap on the lower rigm
board, TB3, as shown in the diagra rru
There is athird speaker shown in the diagram, labelled
CENTER 5PKR. (OPTIONAL). Aresistance symbol is
shown inserieswith this speaker, as well. This resist-
ance symbol stands for an attenuator to reduce th- •vel
of the center speaker appreciably below that of the
channel land 2speakers so asto produce "eenterfill"
without markedly diminishing the stereo effect. For
this purpose we recommend an adjustable 50 ohm, 25
watt wi re -wound dropping resistor suchastKe Obmite
''Dividohm 1',' mounted on the rear panel of the center
chameT speaker adjacent to the speaker terminals.
Connect the sliding divider on the resistor to one of the
speakerterminals, allowing enough slack to permit the
slider to be moved along the body of the resistor. Now
connect the other speakerterminal to the extreme left-
hand terminal on the upper right board, TB2, on the
amplifier, and then connect one end terminal of the.
dividing resistortothe same impedance tap on the left
board, TB1, used for the channel 1speaker. These
connections are shown in the diagram*
The speaker connection diagram si Ik-screened on to the
rear apron of the amplifier is reproduced in Fig. k
with additional polarity Indications which will assist in
phasing the speakers properly if your speakers are mark-
ed as to polarity* Aphysical representation of the
speaker connections Is glvOTi inFIg. 2* if your speakers
are not marked as to polarity, use the phasing method
given below.

Set the speakers together, including the center speaker
if you are using one. Listen to amonophonic source
with plenty of bass material through both channels, end
all speakers, afonce, Temporarilydisconnecf one lead
going to the center speaker. Now reverse the connec-
tions to one outside speaker. If the bass is fuller, the
two outside speakers are now in phase. If the bass is
thinner, restore the original connections to this outside
speaker. Nowre-connect the lead previously removed
fromthe center speaker. If the bass isfuller, the cen-
ter speaker Is in phase wi th the outsi de speakers. If the
bass Is thinner, reverse the connections to the center
speaker.
NOTE: We do not mean to give the impression that a
center channel speaker is normally necessary In astereo
Installation. We consider it, rather, to be aconven-
ient facility In the case that the channel land2speak-
ers have to be spread apart more than the normal 8to
10 feet, or that, with normal spacing, listening at
close quarters Is often necessary. Underfhese circum-
stances the sound from the channel 1and 2speakers
may become disassociated, resulting in aphenomenon
known as "hole-in-the-middle". The center channel
speaker is aremedy for this situation.
AC POWER CONNECTIONS
Plug the line cord info a117VAC, 60 cps power line
outlet only. ADC powersource will cause severe dam-
age to the unit.
Two convenience outlets are provided on the rear apron,
one switched and oneunswitched. The unswitched out-
let should be used with record changers, turntables, or
tape decks (devices which can sometimes be harmed if
turned off simply by removing power) if it Is not con-
venient to plug them directly into the power line. The
switched outlet is for use with tuners. Acube tap may
be used if more than one connection is to be made to
an outlet.
A3ampfuse is provided on an extractor post mounting
on the rear apron. Thisfuse protects only the ampli-
fier, not any equipment plugged into the switched
convenience outlet.

OPERATION OF CONTROLS
SELECTOR Switch: Used to select any input or pair of inputs as follows:
POSITION SOURCE INPUTS COMMENTS
TAPE /AUX. Pre-amp! Ifled tape TAPE 1&TAPE 2
MX/AUX. FM Multiplex Stereo MX 1&MX 2
FM-AM FM tuner &AM tuner FM 1&AM 1FM only with MODE Sw at
MONO 1
AM-AM* AM tuner AM 1Set MODE Swat MONO 1
PHONO AStereo mag* phono cartridge PH. A1&PH. A2Set MODE Sw at MONO
1-2 to play mono record
PHONO BStereo mag. phono cartridge PH. B1&PH. B2Set MODE Sw at MONO
1-2 to play mono record
Stereo tape head in deck without
preamplifiers
TAPE HD. 1&TAPE
HD. 2
MODE Switch: Used to select mode of operation
POSITION OPERATION COMMENTS
CH. 1CH. 1Input out CH. 1speaker For checking left side of stereo program
CH.2 CH. 2input out CH* 2speaker For checking right side of stereo program
STEREO CH* 1input out CH. 1speaker
CH* 2input out CH. 2speaker
Should normally give left side of program out
of left speaker, and right side of program out
of right speaker
REVERSE CH. 1input out CH.2 speaker
CH* 2input out CH. 1speaker Use If left side of program is coming out of
right speaker when set at STEREO
MONO 1CH. 1input out CH. 1&2
speakers
Use for all mono listening except when playing
mono record. Used also for checking balance
in Stereo. See BALANCE v' operation.
MONO 1-2 CH. 1plug CH. 2inputs blended
out CH. 1&2speakers
Used only when playing mono record (with stereo
cartridge)
/
*See note on use of AM 2in INPUT CONNECTIONS,

Ifci&iSteJ ST«Q
PAGE 8
BALANCE Control: Used to. achieve equal left and
right side program levels In stereo. Effective in mono
to center the apparent source between the speakers.
Neither channel amplifier Is favored (as to gain)at the
zero setting (mid-rotation). As the control is turned
clockwise from zero, the channel 2Is (right) speaker Is
made louder and the channel 1(left) speaker Is made
softer, whilethe overall level remains about the same.
As the control is turned counter-clockwise from zero,
the channel 1(left) speaker Is made louder and the
channel 2(right) speaker Is made softer, while the
overall level remains about the same.
BALANCE v'(CHECK) Slide Switch: If you have iden-
tical left and right speakers (or dissimilar speakers of
nearly equal efficiency), the BALANCE control can
be set properly by means of the BALANCE v/(CHECK)
slide switch as follows:
1. Set BALANCE (CHECK) slide switch to ON
2. Set MODE switch to MONO 1
3. Adjust BALANCE control for minimum sound
(null) from the left (CH. 1) speaker. There
will be no sound from the right (CH. 2) speak-
er. If the BALANCE control Is turned either
direction from the proper setting (null), the
sound level from the left speaker will increase.
4. Return the MODE switch to STEREO or RE-
VERSE if the source is stereo.
NOTE:
In the "null" method of balancing just described, this
is what isbeing done. An identical signal is fed to the
channel Iand 2amplifiers at the high level input
points (setting MODE switch toMONO 1). Adummy
load is internally substituted forthe channel 2(right)
speaker and the channel 2output signal Is fed back
through aprecision dividing network to the input of
the channel 1power amplifier (setting BALANCE n/
switch to ON). The channel 2output signal is out-
of-phase with the input signal to channel 1and tends
to cancel or nullify it. When the BALANCE control
is set so that the portion of the channel 2output signal
fed to the channel 1power amplifier input is equal to
the channel 1signal at this point, almost complete
cancellation (null) occurs and the output from the
channel 1speaker is at aminimum.
This method of balancing jchieves equality of gain in
the channel )and 2amplifiers from the high level in-
puts to the speaker outputs. The preamplifiers, which
are ahead of the high level input, are audibly nearly
equal In gain because of feedback. If, upon returning
the MODE switch to STEREO or REVERSE after setting
the BALANCE control by this method, audible balance
is not achieved, the indication is that the sources feed-
ing the amplifier are not equal. If the sources have
their own level controls, such as FM or AM tuners or
Multiplex adaptors, then these level controls should
be set to equal output by successively setting the MODE
switch ats/CH.l andv/CH. 2while adjusting the source
level controls for equal output from each speaker.
Once the source levels have been adjusted, the null
balancing method described previously will work ef-
fectively*
If one speaker Is alittle more efficient than the other,
you may pad down the more efficient speaker by aseries
resistor up to half the rated speaker impedance (more
will unduly deteriorate speaker damping). In order to
make the convenient null balancing method effective.
If the speakers are grossly different in efficiency, you
will have to adjust the BALANCE control by succes-
sively setting the MODE switch at vXCH.l and s/CH.2,
while finding the BALANCE control setting that pro-
duces about equal output from each speaker.
If astereo phono cartridge has amarked difference in
output between the two sides, you will have to adjust
the BALANCE control setting until audible balance is
achieved, while successivelysetting the MODE switch
to\ACH. 1and\ACH, 1and v^CH. 2, when this input
Is selected.
LEVEL control: Used to adjust the listening level in
both channels. The BALANCE control is adjusted after
setting the LEVEL control. Substantial changes in
LEVEL control setting may require re-setting the BAL-
ANCE control. Adjust the output level controls in
tuners, multiplex adaptor, and tape machines with pre-
amplifiers, to match the sound level obtained on phono,
if possible. If any of the high level sources can not
provide high enough output to match phono, simply set
this source to maximum output.
LOUDNESS slide switch: Acharacteristic of human
hearing is thatsensitivity to bass tones diminishes more
rapidly, a's the listening level Is lowered, than sensi-
tivity to middle and high frequency tones. Many people
find the audible loss of bass at low listening levels un-
satisfying* Setting the LOUDNESS slide switch to ON
provides acompensating amount of bass boost at low
listening levels. Do not leave the LOUDNESS switch
at ON when listening at normal volume, since the
amount of bass boost provided will usually be excess-

ST40
ive and unmusica I* Some people prefer not to use loud-
ness compensation at al I, because it does not correspond
to any natural listening condition at alive performance*
BAS$CONTROLCH.1,BASSCONTROLCH. 2(CON-
CENTRIC): The plus sign on the right side of the dial
Indicates that clockwise rotation from the mid-point
(0) of either control Increases (boosts) bass response;
the minus sign on the left side indicates that counter-
clockwise rotation from the mid-point decreases (cuts)
bass response. There is no interaction with the TREBLE
control* Start all adjustments with this control set at
the mid-pofnt (0), which is called the “flat" position
since bass response Is neither cut nor boosted at this
position.
TREBLE CONTROL CH. 1, TREBLE CONTROL CH.2
(CONCENTRIC): The plus sign on the right side of
the dial indicates that clockwise rotation from the mid-
point (0) of either control increases (boosts) treble re-
sponse; the minus sign indicates that counter-clockwise
rotation from the mid-point decreases (cuts) treble re-
sponse. There is no interaction with the BASS control.
Start all adjustments with this control set at the mid-
point (0), which is called the "flat" position since
treble response Is neither cut nor boosted at this posi-
tion*
The amplifier ON-OFF power switch is ganged with
the CH.2 TREBLE control* Note the word “OFF" on
the panel |ust beyond full -counter-clockwise rotation*
The plain circle symbol preceding it indicates that the
power switch is ganged with the CH. 2control. Turn
the amplifier off by turning the CH.2 TREBLE control
beyond full counter-clockwise rotation until the power
switch clicks to OFF* Turn the amplifier on by turning
the CH.2 TREBLE control clockwise from OFFand set-
ting it at the mid-point (0) or some customary setting
^of the CH. 2TREBLE control you may use.
LO FILTER slide switch: Set to ON when it Is desired
to cut low frequency response below 100 cps because
of rumble in aphonograph or even in broadcast program
material. Phonograph rumble Is usually at about 29
cps and may well not be directly audible. Sometimes
it can be at amuch lower frequency, which is defin-
itely not directly audible* However, the effect of
rumble can be heard even the rumble itself Is not* It
manifests itself by using up amplifier power at low
frequencies and can even overload the amplifier* If,
at normal listening levels on phonograph, setting the
LO FILTER to ON definitely results In "cleaner", less-
distorted sound, the indication isthatyour phonograph
PAGE 9
suffers from excessive rumble. Whether it is worth
doing anything about it, depends on the installation,
if you have Inexpensive speaker systems that do not
produce substantial undi started sound below 80 cycles,
you mayjustas well live with the rumble and eliminate
its bad effects by using the LO FILTER. If you have
made aconsiderable investment in speakers, partly In.
order to obtain full, undistorfed response below 80
cycles, you may not want to forego full bass response.
In the latter cases, have the phonograph examined by
aqualified service man to see If the rumble is caused
by adefect that can be remedied.
HI FILTER slide switch: Set to ON when it Is desired
to cut high frequency response above 5000 cps. Use-
ful for minimizing extraneous noise when listening to
narrow range AM broadcasting, for listening to noisy
or worn records, and for reducing the annoyance of
excessive distortion from any source.
TAPE MONITOR slide switch: Useful with complete
tape machines (including record and playback elec-
tronics) that provide off-the-tape monitoring facilities
while recording. In this situation, setting the TAPE
MONITOR slide switch to ON permits you to hear the
program being recorded directly from the tape.
MAINTENANCE
INSTALLATION PROCEDURES
FOR MINIMUM HUM
AC LINE CORDS: Hum can usually be reduced by the
following procedure, after all the equipment used with
the amplifier is connected to It and plugged in.
1. Turn on all the equipment used*
2. Reverse the amplifier's AC line cord plug In the wall
outlet to see If hum is reduced. Leave it in the position
that results in least hum.
3* With the SELECTOR switch, select aparticular
piece of equipment, and determine the insertion posi-
tion of its AC line cord plug that results in least hum.
4. Repeat step 3for every piece of equipment used
with the amplifier.
When this is done, proceed to HUM BALANCE adjust-
ments.

ST4Q
PAGE 10
HUM BALANCE; Separate filament windings and hum-
bala nee controls are provided for the two channels, so
that an optimum hum balance setting can be found for
each channel, rather than acompromise setting for
both channels* Connect the phonograph and leave it
shut-off with the tone arm at rest. Set the SELECTOR
to the PH. Aor PH. Bposition depending on which in-
puts are used. Set the MODE switch at v/CH. 1,
BALANCE at 0, LEVELat 10, BASS 1&2at 0, TREBLE
1&2at 0(amplifier turned on). Setall slide switches
at "off" (down). Adjust the channel 1hum-balance
control (R-77)witha screw-driver until the hum heard
from the channel 1speaker is at aminimum* Now set
the MODE switch at v/CH. 2and adjust the channel
2hum-balance control (R-78) until the hum heard from
the channel 2speaker is at aminimum. See Figure 3
for the locations of R-77 and R-78*
GROUNDING; The cause of phonograph hum maybe
ametal pick-up arm not grounded to the cable shield
(trya good single ground connection to the cable shield
from turntable frame, pick-uparm, and cartridge case),
direct hum pick-up by the magnetic cartridge from the
record player motor (try using arubber mat on the turn-
tableto Increase the separation of the pick-up from the
motor), or pick-up from apower transformer or other
magnetic field in the vicinity (try moving phonograph
away from suspected source). Check also that the phono
input cable shielding is grounded to the amplifier chas-
sis at one point only, through the skirt of the input
connector where it plugs into the amplifier. Finally,
try agood building ground, such as aconnection from
acold water pipe terminated under the channel 2, 4Q
Impedance tap (ground) on the rear apron of the ampli-
fier. Do not connect such aground wire to other com-
ponents in the system. If possible, let each channel
be connected to the amplifier usinga separate shielded
cable to the amplifier input. It is also desirable that
the ground leads on both cables not be connected to-
gether at any point —not even at the cartridge. How-
ever, with some cartridges, it will not be possible to do
this. In this case, just disregard this* last Instruction.
SERVICING
GENERAL
Your amplifier should require little service except for
normal tube replacement. We recommend no substitu-
tions for the tube types used in this amplifier except as
stated. All the tube types used are distributed nation-
ally, but replacements can be obtained directly from
E1CO if desired.
To facilitate servicing, remedial and trouble-shoot-
ing procedures have been provided in the TROUBLE-
SHOOTING CHART that follows. AVOLTAGE AND
RESISTANCE CHART Isalso provided asan aid in locat-
ing defective components. DC operating voltages are
given both at no signal and signal developing 20 watts
output, as well as the corresponding Ike signal volt-
ages.
TROUBLE-SHOOTING
PROCEDURE©
Connect astereo phono and apair of speakers to the
amplifier as described in INPUT CONNECTIONS and
OUTPUTCONNECTiONS. Do not operate the ampli-
fier without speakers or equivalent loads connected
exactly as described. Set the SELECTOR switch to the
corresponding phono position (PH. Aor PH. B)and the
MODE switch to STEREO. Play aknown high quality
stereo recording on the phonograph. If there is no
output to the speaker, or if the output is low or audibly
distorted, proceed to the checks for those symptoms,
if there is excessive hum in the output, disconnect the
phono input cable from the amplifier and short the phono
input jack to chassis, if the hum disappears, the trouble
is not in the amplifier but in the phonograph or In the
connection to the amplifier. In each case, check for
the trouble in the amplifier which seems defective. If
both amplifiers are defective, check the power supply.
Excessive hum on other inputs may be checked in a
similar manner. Disconnect the input cable In question
and short the particular input jack to the chassis. If
the hum disappears, the trouble Is external to the amp-
lifier. Note that on all inputs, the braid of the input
cable should connect to the amplifier only through the
skirt of the input connector* The cause and remedies
for the following symptoms are then based on the assump-
tion that checks made In the manner described above
have eliminated the possibility of the trouble being
external to the amplifier*
If trouble Is no output or low output, check AC signal
voltages and DC operatingvoltages starting at the in-
put, and work step-by-step toward the output in each
amplifier* Set the LEVEL control to maximum (10), the
BALANCE, BASS and TREBLE controls to their mid-
points (0), the SELECTOR switch to PH. Aor PH. B
and the MODE switch to STEREO. Feed a1000 cycle
sine-wave signal from an audio signal generator through
aprecision 100:1 attenuator to the phono inputs selec-
ted. The attenuator permits obtaining a level of 0. 003
volt fed into MAG. PHONO from an audio generator
output of 0.3 volts, which can easily be. measured on

PAGE 11
the lowest AC volts range of yourVTVM (also improves
signal to hum from generator). Use ahigh input imped-
ance VTVM for all AC signal voltage measurements; a
VTVM or20, OOQQ/v VOM for DC volts measurements.
If the trouble is an excessively distorted output, try tube
replacement, signal tracing, or proceed directly to volt-
age and resistance measurements.
When the defective stage is localized, proceed to a
resistance and voltage check of the stage, using the
data in the VOLTAGE and RESISTANCE chart. Dis-
connect the amplifier from the power line and discharge
capacitors prior to making any resistance check, and
prior to removing any or all of the 7591 output tubes.
Do not turn the amplifier on with any of the output
tubes removed.
TRANSFORMER TEMPERATURE
The transformers used In this unit run at atemperature
less than 195°F despite the fact that the safety limit is
at amuch higher 221°F. Although 195°F is cool for
atransformer, it is very hot to the touch. Transformers
which seem too hot when touched with the hand, are
usually good and are actually not overheating.
Output transformers usual 1yrun cooler than power trans-
formers. Some output transformers may appear hotter
than others due to being located near hot components
such as output and power tubes and powertransformers.
SERVICE
If trouble develops in your instrument which you can
not remedy yourself, write to our service department-
listing all possible Indications that might be helpful.
List, also, any code numbers in red under the words
INSTRUCTION MANUAL on the cover. If desired,
you may return the instrument to our factory where it
will be placed in operating condition for $13.50p!us
the cost of parts replaced due to their being damaged
in the course of construction. NOTE; Before return-
ing this unit, be sure all parts are securely mounted.
Attach a tag to the instrument, giving your home ad-
dress and the trouble with the unit. Pack very care-
fully In arugged container, using sufficient packing
material (cotton, shredded newspaper, or excelsior), to
make the unit completely immovable within the con-
tainer. The original shipping carton is satisfactory,
providing the original inserts are used or sufficient
packing material inserted to keep the instrument im-
movable. Ship byprepaldRailwayexpress, ifpossible,
to Electronic Instrument Co., Inc., 33-00 Northern
Blvd., Long Island City 1, NewYork, Return shipment
will be made by express collect. Note that acarrier
cannot be held liable for damages In transit ifpackinq
IN HIS OPINION, Is insufficient.

STOP
TROUBLE-SHOOTING CHART
PAGE 13
SYMPTOM CAUSE REMEDY
Amplifier causes power line fuse
to blow. Power line fuse blows
again with VI 1out of its socket.
Line cord, J16, primary or high voltage
secondary windings of T3 shorted Infern-
ally or externally (wiring).
Replace or repair.
Amplifier causes power line fuse
to blow. Power line fuse does
not blow again with V11out of
Its socket.
Defective Vll, C35, V7/V8, V9, V10; T1
or T2 primary shorted internally or
externally.
Replace or repair.
Any or half of tube filaments not
lit.
Open tube filament.
Open lead from one of the 6. 3V windings
of T3.
One 6. 3V winding of T3 open.
Replace or repair.
^Output tube bias too high
(resulting In distorted output
waveform). "“M°
Open R73, R74. Replace or repair.
DC voltage at VU, cathode
(pin 8) Is Incorrect as specified
below.
a) No voltage. Defective VI 1.
C35 shorted Internally or externally.
Replace
Replace or repair.
b) High voltage. Connection from C35 to pin 8of V11
Is broken.
Connection to center tap of h.v.
secondary winding of T3 open.
Output tubes, V7,V8,V9, VI 0over-biased
or not drawing current. May result from
open R73, R74,
Repair
Check possible causes and replace
or repair.
Check possible causes and repair.
c) Low voltage. Excessive current drain In amplifier.
Defective VI
1
See trouble-shooting typical stage.
Replace
Excessive hum on mag. phono
tape head or mic.
VI or V2 defective
FIl. leads dressed too close to grid lead.
Tube shield not making electrical contact
to base or base not making electrical
contact to chassis.
Shielding and grounding of wiring to Input
Jacks not exactly as Instructed and shown
in drawings.
Replace
Dress fil. leads away from grid lead.
Check and correct.
Correct.
Excessive noise on mag. phono
or tape head.
VI and V2 and contacts dirty. Clean thoroughly with carbon
tetrachloride.
Sustained oscillations. Poor dress of output transformer T1 or T2
leads.
Dress all input leads and Tl, T2 leads
away from each other. Keep Tl, T2
leads away from Input jacks.
Sustained microphonics on mag.
phono, tape head or mic.
VI or V2 defective. 'Replace
Hum on all Inputs V3 or V4 defective, not properly shielded,
or dirty sockets and contacts.
Dress of power transformer T3 leads.
Replace, correct, or clean.
Correct

PARTS
LIST
Ibtiaai stao
PAGE 14

LACEMENT
PARTS
LIST
(CONTINUED)

NW] ST4Q
PAGE 16
VOLTAGE AND RESISTANCE CHART
Pin*
Column 1
DC volts at 20 watts each
channel
Column 2
DC volts at no
signal
Column 3
AC volts (signal) at ,0023V
into Mag. Phono Input
Column 4
Resistance in ohms. Pin
8of XVI 1grounded
VI,
2
1107 1-13 .275 75K
200.018 {. 5Meg
3.0.9 .0.83 .01 1150
415 14 125-175
51.5 14 125-175
638 41 .018 355K
70 0 .0023 113K
80,5 .0.5 .0027 2300
915 14 125-175
V3,
4
154 50 0.86 aafe—£$
.. 31.75 LS3 fe Hjpl
mu III /iIMIW'hi.' ill
1
'V'V c>’Tji ’83K
SBs&A?*' 0.064 320K
.42QHHM
V5,6 i195 .215 92K
86 89 ... ...... 340K
393 97 82K
4125-175
sssiss ^125-175
89 340K
-.-W-
.
-y* .300K
1. IK
125-175
V7, 81008.1 330K
V9, 10 2 15 14 125-175
3395 396 220 170-210
4310 318 2.7 1800
515 14 ,05 125
6.008.1 330
K
715 14 125-175
8310 318 .23 1800
Vll 1
2402 407 >30K** *J
3
4335* 335* 20-35
5
6335* 335,:’20-35
7
8402 407 >30K** V
*AC 60 cycles
**Short From pin 8of XV11 to ground removed
Note: Throughout voltage checks, adummy load must be connected across each amplifier output.
Column 1-Feed aIke signal into TAPE/AUX, Jinput. Set ST-40 controls as follows; SELECTOR switch at TAPE/AUX. ,MODE switch at MONO 1,
BALANCE control at 0, LEVEL control at 10, BASS controls at 0, TREBLE controls at 0, and all slide switches to the down (off) position. Adjust
audio generator output for 20 watts output each channel.
Column 2-Remove input signal. Use same control settings as in' Column 1.
Column 3-AC signal voltages checked one channel at atime. To test Channel 1amplifier, feed a.0023 volt, lkc signal from an audio generator to the PH. A1
input. Set SELECTOR switch at PH. A, MODE switch at \/CH. 1, and all other controls as given for Column 1. To test Channel 2amplifier,
feed a.0023 volt, lkc signal to the PH. A2 input and set the MODE switch at \/CH. 2.
Column 4-Set controls as for Column 1. Disconnect unit from AC line and remove all input and output connections. Short pin 8of XVI lto chassis ground
with ajumper throughout resistance measurements, except when resistances ot XVII pins are being checked.