McMartin LT-80A User manual
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Transistor
Audio
/
PA
Amplifier
_
ode
T-BOA
lnstru
,
ct
1
l1
on
Manua
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D
RIPTJ
lartin
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att
udio/ P -
typ amplifi.r m r,
ia.l
a_ppli
·on .
Tran
,is,
tor
d i l
pr
iding
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rm
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m 11 i handlin
in
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from
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noti
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our
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-
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•r, phon ir
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nd
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tilit
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SPECIFICATIO
NS
Power
Output
......
, . , .
..
. 8 watts rms @ 1000 cps
12 watts music
power
20 watts
peak
power
Frequency
Response
....
. . .
30
to
1.5
,000 cps
±2
<lb
20 to 20,000 cps
±3
db
Distortion .
..
.
.......
. .
....
Less than l
'<
50
to 15,000 cps @ l
watt
Less than l % @ 1000 cps @ 8 watts
Il
um
& 1oise
Microphone . . .
-60
db
below 8 watts
Program . . .
........
....
-7
0
<lb
below 8 watts
Phono (with P
II
-6A)
...
..
-60
db
below 8 watts
Inputs
Microphone . .
.........
. . Hi-Z; 150 K ohms, .008 v for 8 watts
Program
. . . . . .
........
Bridging;
10
K ohms, 0.8 v for 8 watts
Phono (with PH-6A)
.....
Magnetic, ceramic, crystal cartridge
600
ohm
(with MT-6)
.....
Balanced:
-10
clbm for 8 watts
Tm~er (w
ilh
PII-7)
.......
HiZ
; 270 K ohms, + 5
db
gain increase
Outputs
. .
.........
.
....
4, 8, 16, 150 ohms; 70.7 v/ 600 ohms
Controls
...
.
...
.
.........
Microphone Cain
Program Cain
Tone
(cut to
-20
db
@
10
,000 cps)
Power Of\'-OFF switch
Semi-conductors
....
Q-1
2N5Q8;T2391
Q-2, Q-3 2 1508/
SA-100
Q-4 2 ll
371'R69
1
Q-5 2 1
508/
Cll36
Q-6
2Nll02
Q
-1,
Q-8 2Nl.501
SR-1, SR-2 1Nl693
Power Supply . . . . .
..
.
..
120 VAC, 50 60 cps, fused,
18
watts max
Ambient Te
mperatur
e . .
..
Full pC'rformance to 130°F
Dim
ensions & Finish
....
..
9''
w x
7"
d x
4½"
h, Black & Natural
Cray
Shi
pping
,veight
.........
6 lbs.
No
t
e:
• Th,•
program
Bridginp; Tnput mny
be
com1<•t
•
ted
directly
to
n low im-
pedance
or
telephone line without
lo,
~
of
)!nin
or
re~vonsc
diaractcr-
i~tics.
•
The
tone
con
tr
ol
t!oC'.s
not
affect
the
mi
cropho
ne
c
ir
cuit.
WARRANTY
Md,Iartin
Broadcast and Audio
Pr
od
ucts
arc
warranted to be
free from
def
ec
ts in workmanship - FOREVER.
At
our
discretion, we will exchange
or
r
epair
any defective
un
it
or component,
at
an
y time,
without
charge. Material and com-
ponents are
guaranteed
for a minimum period
of
90 days from
th
e
date
of
original purchase. Transportation charges must
be
pr
e
paid
on
eq
uipment returne<l for warranty service.
This
warranty
does
not
extend to
any
of
ou
r products which
have
been
subjccte<l to misuse, neglect, accidents, incorrect wiring
not
our
own, improper insta
ll
ation, or to use in violation of t
he
instructions
fu
rnished
by
us; nor to units
that
have
been
altered
outsi
de
our factory.
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CONNEC
TIONS
Care
should
be
taken
to
see
that
input
and
output
connections
arc
made
properly
and
sec
ur
el
y.
Adequate
shi
ck
l
ed
ethic
should
be
used
especially
with
a
microphon
e
or
phonograph.
Pr
eferably
use
spade
lug
s for
connectio
n
to
all
sc
r
ew
terminals.
To
provide
maxi-
mum
ve
r
sa
tilit
y
consiste
nt
with
minimum
cost,
the
c:ircuib·v
of
the
LT-
80A is
arranged
so
that
only
one
(1)
of
fom
(4)
available
t>rogram
inputs
can
be
used
simulta
n
eous
ly
with
the
microphone
input
,\t
~rny
one
time.
l ) 10
Kohm
Brirl
gin!{
Jnput
:
Cunnn·liun
is
mndc
to
the
1:ihck·cl
'l
'rcw
tl
·
nninnl
anoss
any
low
or
mnlium
im1wtl:111ct•
~ourcc. \Vilh u
\'Cry
high
impedance
tht·re may
be
somL'
lou<linl,(
cffoct. In thii.
t·asL',
me
thL·
1'11-7°.
2) (
JOO
ohm
B
ala
n
ce
d
lnput:
For
GOO
ohms
, insert
the
1ilu!(-i11
1'tod(•l
~IT-6°
transformer
into
the
9-pin
,oeket
and
connt·ct
the
li111•
to
tilt' labeled
screw
ll'rminals.
Either
sill<'
m
ny
be
grounded
if
unbt1lnnt·L•d
line
is desired.
3)
Phon
ograp
h:
Fnr
n m:ignetie,
ceramic,
or
crystal
phono
input,
in,erl
tlw
plug-in
l\loclcl PH-6AO
Phono
Preamp
into
the
9-pin
~ockt•t
an<l
connect
,I
~hielded
<:able
from
the
carlTid~e to
the
phono
jack.
4)
Hi
Z (
Tuner
): A 5
db
l,(nin
incrPasc
and
270
K
ohm
input
impedance
i,
available
by
inscrlinl,(
the
Pll-7°
Preamp
into
the
9-pin ~ocket.
The
input
connection is
then
made
by
shielded
cable
to
the
phono
jack.
0
Optionally
available
l\Iicrophone
Hi
gh Impedan
ce
: T
he
microphone
ioput
circu
it
is
factory
wired
for
operation
w
ith
any
high
imp
edance
microphone.
Th
e
micro-
phone
connecto
r
is
the
shorting
type.
Low
Impedance: If
operation
wit
h a
low
impedance
micro-
phone
is
desired,
modi6cation
at
the
input
c:ircuitry is simple. R
efer
tu
the
schemat
ic
indicating
the
"Changes
for
Low
Z ~l
icrophonc.''
OPERATION
A
specia
l
feedback
circuit
is
incorporated
in
the
amp
lifier to
protect
the
transistors in
case
the
speaker
loud
is acci<lentally
re-
moved
or
sho
rt
e
d.
The
power
tran
sistors are
externally
fused
for
protectio
n
against
overload.
:o
warm-up
time
is
necessary. Sufficient
space
should
be
a
l-
lowed
around
the
amplifier
for
air
circulation.
After
volume
and
tone
controls
are
set
to
the
desired
levels.
the
knobs
may
he
re-
moved
and
replaced
with
the
plastic
Contro
l
Guards
(suppli
ed
with
your
amplilier) to
prevent
tampl'l'ing.
SERVICE
l\
f
aximum
power
ou
tput
with
a
sine
wave
signa
l
may
be
checked
at
any
freq11cncy
11p
to
10.000 cps. A
sustained
tone
above
approxi-
mate
ly 5000
c:
ps
should
not
be
applied
for
more
than
a few
minutes
or
excessive
transistor
h
eating
will result.
This
cond
ition will
blow
th
e
prot
<'c
ti
ve
fuse
(r
ear
chassis).
ll
igh
frequencies
at
l
ow
p
ower
output
will
hav
e
no
adverse
effect. The
LT
-80A will
supp
ly full
power
co
ntinuousl
y
with
normal
program
material.
Dama
ge
to
tran
sistors
may
result
if
any
wiring
is
shor
t
ed
wh
ile
servicing
or
circuit
h·acing. Avoid
removing
transistors from
thefr
sockets
while
th
e
power
is
turn
ed
on.
lf
r
ep
la
cemen
t
of
ei
th
er
power
transistor
is
necessar
y,
be
sure
to
coat
b
ot
h sides
of
the
mica
insu-
l
ator
with
Silicone Jel. A
powe
r line
fuse
is
lo
ca
t
ed
und
er
the
chassis
and
is
accessible
by
rem
oving
th
e
bottom
cove
r.
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