McMartin MS-25B User manual
www.SteamPoweredRadio.Com
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MCMartin.
I.
SPECIFICATIONS
POWER
OUTPUT
•..
DISTORTION
.....
.
OUTPUT
REGULATION
. .
..•
FREQUENCY
RESPONSE
Mualc Channel
..
Mic
Channel
•...
Aux
Channel
.•..
Mualc Tone
Compenaatlon
..•
HUM & NOISE
Mualc Channel . .
Mic
Channel
.•..
Aux
Channel
....
INPUTS
(4)
Mualc
.........•
Microphone
.....
•
(2
optional)
Auxlllary
......
.
GAIN
Mualc
Bridging
600-
ohm
with
optional
MT-4,MT-6
..
.
Matching
....
.
Auxlllary
......
.
Microphone
..
...
.
OUTPUTS
........
.
......••.•.•...•
25
watts rms
35
watts
music
50
watts
peak
. . . . .
Less
than
2%
THD
@rms
rated power 50-15000
Hz
...••...
..
••.•.........
2
dB
.
•......
±1.0
dB
30-
15000 Hz
±1.5
dB
20-20000
Hz
..•..•...
Fl
at
response
t2
dB
50-15000
Hz
Equalized
for
speech,
-12
dB
@ 50
Hz
...•.....
±1.5
dB
20-20000
Hz
.
..
.....
Bess
±15
dB
I 50 Hz
Treble
±1
5 dB@ 15 kHz
...........
70
dB
below rated
power output
•..........
60
dB
below rated
power output
.•.........
70
dB
below rated
power output
..•........
25K-ohm standard
10K-ohm bridging
or
600-ohm
matching
with
optional MT-4
or
MT-6
input
transformer
.........
50-150-ohm balanced
...
40K-ohm nominal,
auxiliary
gain control standard
. .
..
• •
••
•. . . . . . • •. . . . .54
dB
.••.••.•
•
•••••••••••.•
64
dB
.
..••.................
44
dB
........•............
108
dB
•..•
8 ohm unbalanced, 25 and
70.7 V balanced
11.
GENERAL DESCRIPTION
BASIC
AMPLIFIER
The
amplifier
consists
of
a complementary power amp-
lifler
circuit,
power supply, and speaker
line
matching
transformer.
This
basic
unit
may
be used
for
back-
4/75
ground music applications where microphones
end
tone
equalizatlon are
not
required.
Provision
is
made
for
two
medium
level
Inputs; (1) music Input -which may
be
used unbalanced or balanced
with
the MT-4
or
MT-6
(600 ohms
or
10
K bridging) transformers, front and rear
panel control, (2)
auxiliary
inputs which
may
be used
for
an
auxiliary
program source.
This
Input
is
unbal-
anced
only
and may be adjusted by a r
ear
panel screw-
driver
adjust
control which comes as standard equipment.
Output connections provide for
either
8
ohm
unbalanced
load
or
25
volt
and 70.7
volt
balanced speaker systems.
A three
wire
unswltched
utility
outlet
(300
watt
capa-
city),
. AC power indicator
light
and maximum output
indicator
I
ight
also
come standard
with
the basic amp-
1
ifier.
Electrical
protection
is
provided by AC fusing
as
well
es
diode current
limiting
for
short
circuit
fault
protection.
The
basic
amplifier
provides for insertion
of
additional
accessory modules such
as
:me
or
two microphone pre-
amplifiers
with
balanced input, telephone page adaptor,
feedback
type
individual bass and treble controls and
en
electronic
page mute adaptor
for
controlling
all
input
muting.
See
catalog sheets for
full
MSA-Module items.
For
convenience, the most commonly used modules,
MSA-1, 2 & 3 are described here.
TONE
CONTROLS
(MSA
-2)
A separate plug-in
circui
t card (MSA-2)
is
available
for
bass and
treble
tone equalization
for
installa
tions
where
this
is
desired. The tone controls
affect
the
music channel
only
and provide 15
dB
of
bass boost or
cut
and
15
dB
of
treble boost
or
cut. They are screw-
driver
adjustable through the rear panel to prevent
tempering.
The
tone control network
is
of the
active
feedback
type
having
unity
gain
with
the controls cen-
tered. Therefore, the input
sensitivity
does not change
when the controls are
installed.
MICROPHONE PREAMPLIFIER (MSA-1)
The microphone preamplifier
is
a
se
lf
-contained plug-in
module (MSA-1)
with
40
dB
gain,
circuit
board mounted
gain control,
end
mu-metal shielded transformer accept-
ing lo-Z balanced microphones.
The
three stage preamp-
11
f
ie
r provides
for
30
dB
of
overload, Instantaneous
overload recovery,
RF
suppression, paging connection
(12
dB
bass cut), two microphone input impedance taps,
and reversible front panel gain control for
either
exter-
nal
or
concealed screwdriver adjustment.
Either
one
or
two
of
these modules
may
be
installed
in
the MS-25B.
Screw terminal connections are provided on the rear
panel for microphone termination.
PAGE MUTE MODULE (MSA-3)
Microphone and program muting
is
accomplished by a
separate plug-in el
ectronic
gating module.
This
circuit
when
installed
mutes both microphone channels and
leaves the
auxiliary
input and music
in
put
on.
When
either
or
both microphone inputs are activated (by
grounding
the
appropriate mute connection) the music
end
auxiliary
inputs are muted and the microphone
channel
is
activated. A screwdriver
adjust
control Is
also
provided on
the
module
(accessible
through the
rear panel) to
adjust
the
music level
while
the micro-
phone channel
is
activated
If
complete muting of the
music
Is
not desired.
By
changing the location
of
one
resistor
on the power
amplifier
board
It
is
al
so
possible
to bypass the mute
circuit
on the
auxiliary
input chan-
nel to keep
this
input open el
ell
times.
1
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2
If
pr
iority
of Input
Is
desired {MIC-1 over MIC-2,
etc.)
the 'ground' path
Is
simply
run In series through the
muting contacts
as
shown
in
Figure
1.
__
,,.
RACK MOUNTING K
IT
(MRP
-1
)
The
MS-258 requires 3½" of
rack
space and
may
be
rack
mounted by the addition
of
the optional rack
mounting
kit.
TB
-1
--------,
M
ic
Sw
itc
h
-·
~-----
.....
--+..(:}-+---+
To
M
SA
3
_>--,.'~>-+---...-
I
IE
MSA
1
---
~--
----
PBX
PBX
I L ine I
Ck
t
IR
ly
by
1 Tel
co
.J
.._
_______
_
NOTE:
Se
rles
ground
mu
st originate at ampllfle
r.
To
MSA-3
MSA
4
Figure 1 CHANNEL 2 HAS PRIORITY
Ill.
INSTALLATION
AND OPERATION
The
MS-258
is
designed
to
operate from line voltages
of
105
to
125
volts
AC.
Both are equipped
with
power
transformer primary taps for 1
05
-115
volts
AC
and
also
115-125
volts
AC. T
he
amplifier
is
normally shipped
with
the
tap connected
for
115-125
volts
AC.
Actually
higher fine voltages than
this
may be tolerated for
short'
periods
without
endangering the
safety
of
the
amplifier.
The primary tap should
only
be changed
to
the 105-115
volt
position
in
the event
of
sustained
low
line
voltage.
After
selecting
a
suitable
location
for
the amplifier,
remove the top cover and
lnstal
I the necessary acces-
sory
circuit
cards, fine transformer,
etc.
Connect the
speaker
lines
to the 25, 70.7
or
8
ohm
connections as
required.
Also
connect
all
Inputs, unbalanced
or
bal-
anced music inputs, microphones, page mute, etc.
Balanced music Inputs may be connected for
either
10K
ohm bridging or 600 ohm matching Input (connections
are provided
on
the rear
chassis
terminals). Unbalanced
program sources
may
be
fed
to
either
the auxi
llary
Input
(phono plug)
or
the 1
0K
ohm
terminals without the
line
transformer
installed.
(Make sure jumpers are
installed
in
socket from pins 5 to 8 and 6
to
9).
The 10K terminal
marked (G)
Is
the ground connection for unbalanced
input.
Balanced microphone inputs should be connected to the
appropriate screw terminals
on
the rear
of
the
unit.
T
he
ground connections are
for
shield
grounds and for the
page mute ground returns. A three-<:onductor microphone
cord
with
shield
may
be used
with
one lead for the page
mute Iine.
The
page mute
circuit
may
then be activated
by
a remote microphone
switch.
NOTE
:
Always
disable
the microphone audio Iine shunt
switch
when using the
MSA-3 mute
mOdule
(See
Figure
1)
Once
all
connections have been
made
, apply power and
set
controls on front panel
to
the appropriate
levels.
A
gain I
imit
control Is provided on the rear
of
the
unit
to
set
the maximum level
of
the music input. The gain
control
tor the
auxiliary
input, the tone
controls,
and
the music mute
level
controls are
also
located on ·the
rear
of
the
unit.
When
maximum output
of
the
amplifier
has been reached
(with
proper loading) the maximum
output Ilght
wi
II
flash, indicating the 70.7
volt
line
level
clipping
point
has been reached.
This
light
may
flash
occasionally
with
program peaks, but should not
stay on continuously. Overdriving the
amplifier
in
this
manner
will
cause excessive
distortion.
INSTALLATION ANO REMOVAL
OF
MODULES
To
Install
page-mute and tone control modules,
it
Is
necessary
to
remove the
amplifier
top
cover, (remove
jumper from pins 4
and
7 and
resistor
from tone control
socket) and caretuI
ly
plug the
mOdu
les in the approprl
ate sockets.
Position
the :,rinted
circuit
board mounting
stud over the chassis hole and secure board
with
one
number 4-40 screw.
To
Install
microphone preampllflers insert
felt
washers
over control shaft, remove hole plug and
install
preamp-
1
itiers;
then proceed the same
as
above for the tone
controls.
Afte
r the preamplifier
Is
secured, place one
nylon
washer over outside
of
control
shaft
and
install
knob. Squeeze control and knob together gently
and
tighten
set
screw. Be sure control
Is
turned
full
counter
clockwise
and knob pointer
Is
set
over
O'
mark. {7
o'clock
position).
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MC
Martin.
4/75
IV
PARTS
LIST
Non-Standard parts
only
(
all
other
parts available
local
ly)
Basic
amplifier
(Power
amplifier,
power
supply
and
chassis)
SYMBOL
Q-1
Q-2, 3
Q-4, 6
Q-5
0-1,
2,
3,
4,
5
Z-1
R-15, 29,
30
R-
19
R-28
C-7
C-
11
, 12
F-1
PL-1
PL-2
SW
-1
T-1
T-2
*
This
value
may vary from O
to
10 ohms
P/ N
201050
201056
201067
20
1068
210008
220008
400042
502028
400039
600039
600040
280009
291001
291002
480011
900047
910043
PARTS
LIST
MSA-1
(MICROPHONE
PREAMPLIFIER
MODULE)
SYMBOL
Q-1
Q-2
Q-3
R-7
T-1
P/ N
201052
201050
201022
400039
910041
PARTS LIST
MSA-2
(TONE
CONTROL
MODULE)
SYMBOL
Q-
1,
2
Q-3
R-2,
11
P/ N
201049
201022
400042
PARTS
LIST
MSA-3
(PAGE
MUTE
MODULE)
SYMBOL
Q-1
,
2,
3, 4
0-1,
2,
3
0-4,
5
R-3
PIN
201049
220003
220006
400042
DESCRIPTION
Transistor
SE
4010
Transistor
2N 3569
Transistor
MJE
2901
Transistor
MJE
2801
Diode
Rectifier
808
800
PIV
at
750
MA
Diode
Zener
36
Volts
Control 50 K
Linear
*Resistor
3.3
ohm½
watt
Control 50 K
Audio
Capacitor
1000 MFO
at
50
Volts
DC
Capacitor
1000 MFD
at
75
Volts
Tubular
Fuse 0.75 Amp 125
volts
slo
blo
PI
iot
Lamp
WHT
Lens NE 2
PT
Red Lens NE 2
PT
Switch Rocker
Transformer 2-P-117 A
Transformer 2-A-93 A
DESCRIPTION
Transi
stor
SE 4010
Transistor
2N
4249
Transistor
SE
4001
Control
50
K
Audio
Transformer Input Microphone
DESCRIPTION
Transi
stor
SE
4002
Transistor
SE 4001
Control 50 K
Linear
DESCRIPTION
Transistor
SE 4002
Diode
IN 462
Diode
IN 87
Control
50
K
Linear
3
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4
V.
WARRANTY
McMartin
products
or
e
warranted
to
be fr
ee
from
defects
and
work-
manship
for a
period
of
one
year
ofter
shipping
dote
, when
sub-
je
cted
to
normal
usage
and
se
rvice
. Al I
warrant
ies
are
void
if (a)
equipment
hos
been
altered
or
repaired
by
others
without
McMar-
tin's
specific
prior
authorization;
or (b)
equipment
is
operated
under
environmental
conditions
or
circumstances
other
than
those
specifically
described
in
McMartin
literature
or
instruction
man-
uals.
Upon
notification
within
the
applicable
warranty
period,
McMartin
agrees
without
charge,
to
repair,
replace
, or
supply
replacement
ports
for
any
properly
maintained
equipment
or
port
s
that
are
de-
fective
as
to
design,
materials,
or
workmanship
and
that
are
re-
turned
in
accordance
with McMartin's
instructions
to
the
Buyer.
At
McMartin
's
sole
discretion
,
the
Buyer may be
requested
to
re
-
turn
the
defective
port
of
equipment
to
McMartin, FOB Omaha,
Nebraska.
Ports
or
equipment
may be
returned
only
with
McMar-
tin's
prior
authorization
and
must
be
identified
by o return
auth-
orization
number
issued
by
McMartin's
Customer
Service
Deport-
ment.
All
merchandise
so
returned
must
be
sent
transportation
prepaid,
at
Buyer's
risk
.
Full
details
of
the
failure
or
malfunction
should
be
included
so
as
to
expedite
repair
or
replacement.
Re-
pair
parts
or
repaired
or
replaced
equipment
wi
11
be
returned
to
the
Buyer,
FOB
factory.
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MCMartin.
4/75
IV
PARTS
LIST
Non-Standard
parts
on
ly (alI
other
parts
avaiI
able
locally)
Basic
ampI
lfler
(Power
amplifier,
power
supply
and
chassis)
SYMBOL
0-
1
0-2,
3
0-4,
6
0-5
0-1,
2,
3,
4,
5
Z-1
R-15, 29,
30
R-
19
R-28
C-7
C-11, 12
F-1
PL-1
PL-2
SW-1
T
-1
T-2
•This
value
may vary from O
to
10 ohms
P/N
201050
201056
201067
201068
210008
220008
400042
502028
400039
600039
600040
280009
29
1
00
1
29
1002
480011
900047
910043
PARTS
LIST
MSA
-1 (MICROPHONE
PREAMPLIFIER
MODULE)
SYMBOL
0-
1
0-2
0-3
R-7
T-1
PIN
201052
201050
201022
400039
910041
PART
S
LIST
MSA
-2
(TONE
CONTROL
MODULE)
SYMBOL
0-
1, 2
0-3
R-2,
11
P/N
201049
201022
400042
PARTS
LIST
MSA
-3 (PAGE
MUTE
MODULE)
SYMBOL
0-1.
2.
3,
4
D-1,
2,
3
0-4,
5
R-3
P/ N
201049
220003
220006
400042
DESCRIPTION
Transistor
SE 4010
Transistor
2N 3569
Transistor
MJE
290
1
Transistor
MJE 2801
Diode
Rectifier
808
800
PIV
at
750
MA
Diode
Zener
36
Volts
Control
50 K
Linear
•R
esistor
3.3
ohm½
watt
Control
50 K
Audio
Capacitor
1000
MFD
at
50
Volts
DC
Capacitor
1000 MFD
at
75
Volts
Tubular
Fuse
0.75 Amp 125
volts
slo
blo
Pilot
Lamp WHT Lens NE 2
PT
Red Lens
NE
2
PT
Switch Rocker
Transformer 2-P-117 A
Transformer 2-A-93 A
DESCRIPTION
Transistor
SE 4010
Transistor
2N
4249
Trans
is
tor
SE 4001
Control
50
K
Audio
Transformer Input Microphone
DE
SC
RIPTION
Trans
is
tor
SE 4002
Tr
ansistor
SE 4001
Control
50 K
Linear
DESCRIPTION
Transistor
SE 4002
Diode
IN
462
Diode
IN
87
Control
50
K
Linear
3
www.SteamPoweredRadio.Com
4
V. W
ARRANTY
McMartin
products
are
warranted
to
be
free
from
defects
and
work-
manship
for a
period
of
one
year
ofter
shipping
dote,
when
sub-
jected
to
normal
usage
and
service.
All
warranties
ore
void
if
(a)
equipment
has
been
al
tered
or
r
epaired
by
others
without McMar-
tin's
specific
prior
authorization;
or (b)
equipment
is
operated
unde
r environmental
conditions
or
circumstances
other
than
those
specifically
described
in McMartin
literature
or
instruction
man-
uals.
Upon
notification
within
the
applicable
warranty
period,
McMartin
agrees
wit
h
out
charge,
to
repair,
replace,
or
supply
rep
l
acement
por
ts
for
any
properly
maintained
equipment
or
ports
that
ore
de-
fective
as
to
design,
materials,
or workmanship and
that
are
re-
turned
in
accordance
with
McMartin's
instructions
to
the
Buyer.
At
McMartin's
sole
discretion,
the
Buyer may
be
requested
to
re-
turn
the
defective
port
of
equipment
to
McMartin, FOB Omaha,
Nebraska.
Ports
or
equipment
may
be
r
eturned
only
with
McMar-
tin's
prior
authorization
and
must
be
identified
by o return
auth-
orization
number
issued
by
McMartin's
Customer
Service
Depart-
ment.
AlI merchondi
se
so
returned
mu
st
be
sent
transportation
prepaid,
at
Buyer's
risk.
Full
details
of
the
failure
or
malfunction
should
be
included
so
as
to
expedite
r
epair
or
replacement.
Re-
pair
parts
or
repaired
or
replaced
equipment
wi
11
be
returned
to
the
Buyer,
FOB
factory.
-
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I
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www.SteamPoweredRadio.Com
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FRONT PANEL FUNCTIONS
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COMPONENT
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EXAM
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MASTER SCHEMATIC
E-2706
9
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