McMartin LT-80B User manual

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P,o,w·r O · tput
.. l'I quency R pons
SPECIFliCATIO S
atts nns
12 wa m
1 atts p
3 to 15)000 Hz ±.2 db
2.0 to 20 O O. . ±3 b
L O Hz _3db
Input
.- 5 db below
-65db blow
' icr,ophon 0
ce d H' Z or balan d o Z
T
. · ced
Ph -6B) ..
T ·-7) Hi Z (270K
a / PH · f o,
L~ ~ l b
B tc
Outpu -. . . . . . . . . .
lt and ·--
Control·
10 000 Hz)
h
P w r uppl -
d, 20
Full C t 150° F.
Dim nsion-
,,w ½, "h cMar in. blu
anal , uminum
h 'pp· n "\\ - ight . 6 lb .
ACC ES SOR IES
. . . . . . . . -pin mik ma1
. . . . . . . . a r .ain conmol
. Ph no pr amplifier
........ Program preampl:i:8 r
... ... T ·· H d pr am . Jifi. r ( cif 11 t 3-" r
T.4 ,. . . . . . sfoim- 1
RP- 0 . . . . . . . bly for LT-8 0B
f ~6 _ _ . . r
McMa , rtin
LT - 80 ;8
RANSl ' STOR
AMPLIFIER
8 W. ATT
Th f Martin LT.BOB is a · ti ely .
DIO /PA ampU6er ly . ed fo
· und and back un t: .ns. Ou
fonnan quality and ar _ _ ~ _ d.
0 ohms unbalanced
, . Hz.
-7 r
r ami ·
gram
"d d for ·
f :rm - r.
Th peak .r outp u oo ist of balan d 70.7 vol
25 I ts and a normal 8 ohms hn clan . .
PROGRAM INPUTS
15 ,K Ohm Bridging In . put
Th 15,,000 o hm mpu. nn cti. o,n i mad · a th
typ nnina1 n lb. rear of th chassis mark d lSK
tandar-d unbalan brid · input is f r conn 'lion of
m d· um imp dance input.
-.
is moun d · -
y to th 3.
udfor · h
h a:s a r :dio d
·onaJ high ·
- PH~ is
_· t, ~gh
-th · ac,
_ .a phono plug for · . on.
Phonogr-apb
A · ramie or cry ,ta} phouo inpu m y be u ed. by in .- rt-
in , 11 plug-in liod 1 H-· 6B ph n p - amp iut th P RO -

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CRAM TRANS socket and co nn ecting th e shie lded c ab le fr om
th e ca rtrid ge to th e PH ONO juc k.
Tape Head
Di r ec t co nn ec tion to a HiZ tap e p layback h ead .i s possible,
inserting
th e Mo dd PH-8A into the PROGRAM TRA
1S
soc ket
and ronnccting the input to the PU ONO Jac k. \Vh en ordering
th e P ll -8A tap e h ea d preamp lifier, please sp ec if y spee d, ( 17/s ,
3¾, or 71/2 inch es per seco nd ). Us e shielded ca ble a nd a
ph ono pl ug for thi s co nnection.
Lin e Brid ging
Th e optional p lu g-in MT -4 transformer mu st be u se d. The
bnlnn ce d 10 , 000 ohm impe dance e nab l es many nmpli6crs to be
c.-o nn ec ted to a si ngle 600 ohm line without l oa din g. Th e re ar
c ha ssis terminals ar e marked Ll E IN. To preserve go od fr e-
quency response, a s ing le r es istor ( 470 to 680 o hm ~) sh ould be
u se d to te rminate a 600 ohm line for an y number nf bridging
amplifiers.
Li ne lat c hin g
Th e optiona l plu g-in MT -4 tran sfo rmer must be used a nd
PROCRA~I TRANS socket wiring modifi ed for n ba l an cc.• d 600
ohm impcdance. Move th e soc ket wir es connected to pins 5
and 6 to pins 1 and 4. Connect t he input to rear chassis term-
inals marked
LINE IN.
MICROPHONE INPUT
Hi gh lmp ednnoc ( unbalan ce d)
Thi s input is s tanda rd and cnn be used with any high
imp eda n ce typ e microphone. Mike cable le ngth s s hou ld be
limit
ed lo approxim atc ly 20 fl'c t. Note: Th e C- lM con n ecto r
is
fa c tor y in sta lled. lf a two-conductor s hi e ld ed ca ble is used
for a
IliZ mic, itround the unu sed wire to pin l.
Low I mp e dnn ce (bnlan ce d)
Th e o pti onal M T-4 transformer must be used. Any l ow
im pedan ce microphone of 50 to 600 o hms c an be connected.
Scwr:il hundr ed feet of m.ik c ca ble muy be u se d.
Lo w Imp e dan ce ( unbal anc ed )
An optional t.l
T-4 tTansfo rm er mu st be u se d and th e
jump er mu st be wir ed be twc- en pins 1 and 9 on th e ~ !I C
TRANS socket. Th e wirc be tw ee n this co nn cc tor and pin 2
mu st be moved to pin 3. B eca u se th e m ic cable is unb alan ce d,
th e le ngth should be limited to approximately 30 fe et.
The microphone c ircuit will accommodat e virtually all
typ es of mi cro phon es. F or tho se microph on es with extremely
high o
utput levels which may tend to ove rload th e input and
ca u se di stortion, install R20 . (See st·hcmatic.)
OUTPUTS
8 Ohm ( unbnlanc ed)
Generally only a single
spea ker or few speakers arc con-
n ec ted to this output.
70 .7 volt and 25 volt (balanc ed )
The se constant vo ltag e outputs ar e most co nvenie nt for
connec tion to a multipl e sp ea ker installation. The 70 .7 volt
or
25 volt tr ans formers must be u se d with each s peak er syste m.
U tilit y AC Outl et
A
convenient AC outlet oo t he rear of th e chas~is will
handl e loads up to 250 wat ts. Th is ou tl et is not fu se d or con-
tr o ll ed by th e an1plificr power swi tch , SW I.
CONTROLS
Micr o ph on e Gain
Th e MI CROP H ONE contro l, R6 , is u se d for aclj11stinl-!: th1 ·
o
utput l ev el of th e microph one preamplifier QI aod Q2. Il ass
r espo n se in the microphone c hanne l is attenuated for crbl)
voice
amp lification.
Prog ram G ain Co ntr ol
Th e PROGRAM control, R37, is u se d for adjustiniI the
input s ignal level applied to the base of transistor Q3.
Tone C
ontr ol
Th e TONE control, R 34, is u se d for nthmnation of hi gh
fre
quency r es pon se.
0 -OFF Sw itch
The
ON-OFF switch, S\Vl, c.-ontroL; all pow t• r to the unit
~•xcc pt th e ulility AC outlet. A neon indi c..'l tor la mp localed
along side of th e power sw itc h is ill uminate d when th e sw itch
is plat-cd in
th e ON position.
SERVICE
Conne ct io ns
T
he u se of s hie l ded ca ble is r eco mm e nd ed when con -
necting m icr op ho ne s, phonograp hs or similar so ur ce equi p-
me nt to th e arnpli6cr. Car e sh ou ld be tak en lo ~cc that input
conn ect i ons are mad e pr ope rly and securely. Use spade l ugs
for coru)ection~ to all screw-type te nninnl s.
Maint
ena nce
Ad e quat e wn tilalion sh ould be provided for th e amplifier.
Th e externally mount ed fus e, F2 , on lh c r ea r of the c ha ssis is
pr ot ec ti on again st n continuous ove rl oa d. If thh fu ~c foils nfll,r
~cvernl ho
ur ~ of opcra li on. che ck to sec that tlw sp ea k ers art'
correc
tly match ed and th e ru nplifler is not cont i nu ously deliv-
ering m
ore th:111 its rated output. An o th er possible cause of
fu sl' failure is inaudible high fr eq u ency oscillati on applied to
,unplificr
iupul s. Check the spe ak er o utput with an oscill o-
St.'<> tl e as oscillation ma y originate in the input so ur ce (e.g. ta pe
recorder).
Th e speaker and program or mi cr op h one wires
sho
uld not be ins ta ll ed within th e same conduit.
Maximum pow er output with a sine wave signal may bt:
ch
ec ked al any fr e qu en cy up to 10,000 Hz. A sustained t one
above 5000 Hz at full output sho uld not be applied for more
than a few seconds
a., e.xccs~ivc Lr nn~btor h ea tin g will occur
and cause the fu se (F 2) to fail. High fr equenc i es at a lower
pow
er outp ut will not ha ve an adverse effect.
Dam age to tran sistors may r esu lt if any wiring i~ ~ hort ed
while
se rvi cing or circ uit-tra cing. Do not re mo ve transistors
fr om th ei r sock ets whi le pow er is on. If re placem ent of a
power tran sistor b r eq uired, coat bot h sides of th e mica insu-
lat or with Sili co n Gel.
The power fu se , Fl , is l ocated undC'r the c ha s~is nnd is
a1:cessible
wh en l11 e bott om c has sis cover is rem ove d.
ARCHITECTS AND ENGINEERS SPECIFICATIONS
Th e runplifier s hall be a vo lta ge :111d power amplifier cap-
able of 8 walls rm s o utput and shall be rated at 12 watts mu sic
power and 16 watts peak powl'r. Th e microphone circuit shall
be
pr o,.;ded with n socket to ac co mm o di1t e a plug-in trans-
former to
permit the u se of l ow impedan ce micr op hones. 3 pin
(C-1~1) mi crop hone co nn ec tors shall be ~tnndard e quip -

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ment. A high impedan ce program input circuit shall be
provided with a socket to accommodate a plug-in transformer
to permit
th e use of a balanced line with isolation; both match-
ing and bridging inputsshall be available. Screw-type termina-
tion shall be provided for the balanced line input. A screw-
type terminal board shall be provided for all outputs.
Th e amplifier shall have outputs of 8 ohms unbalanced
and 25 volts and 70.7 volts balanced, with a tone control cap-
able
of tr eble cut to -15db at 10,000 Hz. lt shall al so have
separa
te microphone and program controls. An AC power
outlet shall be provided. All transistors shall be provided with
the amplifier.
Th e performance specifications shall be as li st•
ed und er Specifications.
WARRANTY
McMartin Broadcast and Audio Pr oducts are wnrranted
to
be free from defects in workmanship FOREVER.
At
our discretion, we will exchange or repair any de -
fective unit or component,
at any time, without char~e. Ma-
terial and
co mponents ar e guaranteed for a period of 90 days
horn
dat e of original pur chase. Tr ansportation charges must
be
pr epaid on equipment returned for warranty service.
This warranty does not extend to any
of our products
which
ha ve been subjected to misuse, neglect, accidents, in -
co rr ect wiring which is n ot our own, improp er instalJ at ion,
or to use in violation of the instructions furnished by us; nor
to units
that have be en altered outside our factory.
REPLACEMENT PARTS
Symbol Stock Symbol Stock
No. No. Description No.
No. Description
Q-1, Q-3 201049 T
ran sistor SE-4002 R-16, R-17,
Q-2, Q-4,
Q-5 201022 Tran sistor SE-4001 R-18, R-19 502112 Resistor
l0K ohm ½W
Q-6 201052 Transistor 2N4.249 R-23, R-26 502060 Resistor
68 ohm ½W
Q-7,
Ql0
201020 Tran sis tor MC-110 R-24 502096 Resistor 2.2K ohm P
ot ½W
R-20 536005 Resistor 10 ohms 20W
SR-1, SR-2,
R- 33 502110 Resistor 8.2K ohm ½W
SR-3 210008 Di
ode R cc t 8D8
R-40 502084 Resistor 680 ohm ¼W
Z-1 220007 Zener 13V Silicon (lR-13) R-41
533009 Resistor 22 ohm SW
PL-1 291003 Leecraft 3200 N
eo n 125V C-1, C-5 640016 Capacitor
.1 MFD P 80 -20
l00V Di sc
R-1 502118 Resistor 18K ohm ½W C-2, C-13 640025 Capacitor
50 MFD 6.0V
R
-2 502124 Resistor 33K ohm ½W C-3 600011 Capacitor
50 MFD 25 VDC
R-
3, R-31 502130 Resistor 56K ohm ½W C-4 600008
Ca pacitor 250 MFD 25 VDC
R-4 502136 Resistor
lOOK ohm ¼W C-6, C-8 600009 Capacitor 160
MFD 25 VDC
R-5, R-7, R-9, C-7 600013 Capacitor 100 M
FD 64 V
R21, R-25 502104 Resistor 4.7K ohm ½W C-10 640014 Capacitor 1
80 PF 500 VDC
R-27 , R-35, C-11, C-18 600006
Capa citor 64 MFD 64 V
R-36, R-38 502104 R
<:!> istor 4.7K ohm ½W
C-12 650011 Capacitor 270 PF
R-6, R-34, C-14, C-23 600022
Capa citor 320 MDF 6.4 V
R-37 400014 Control lOK ohms
Pot 1/t W
R88, R-22 502116 Resist
or 15K ohm ohm ½W C-16 601020
Cap ac itor JOO() MFD 100 V
R-11 502076 Resistor
330 ohm ½ W C-19 600020 Capacitor 400
MFD 40 VDC
R-12 502102 Resist
or 3.9K ohm ½W C-20 640015 Capacitor .05
MFD P 80-20
100 VDC Disc
R-13 502088 Resistor
lK ohm ½W
C-22, C-17 630026 Capacitor .22
MFD 200 voe
R-14, R-28,
R-32 502068 Resistor 150K ohm ½W
T-1 910016 Trans
fom1 er Output
R-15 533024 Resistor .27 ohm
5W T-2 900007 Transformer Power

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