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O V E R A L L R E C E IV E R S E N S IT IV IT Y M E A S U R E M E N T
A n o v e r a l l m e a s u r e m e n t o f s e n s it iv it y is m a d e as f o l
lo w s :
1.
C o n n e c t an A M s ig n a l g e n e r a t o r to the input t e r m in a ls
o f
the
r e c e i v e r c h a s s i s a fte r r e m o v in g the s h o r t 300 oh m
le a d w h ic h c o n n e c t s to the an ten n a input s t r i p on the b a c k o f
the c a b in e t .
T o m a tc h the g e n e r a t o r to the r e c e i v e r in p u t,
a r e s i s t i v e m a tc h in g n e t w o r k sh o u ld be u s e d .
a g e n e r a t o r w ith a 50 oh m output im p e d a n c e , f o r e x a m p le ,
p la c e a 100 o h m r e s i s t o r in s e r i e s w ith the outp ut t e r m in a l
o f
the
g e n e r a t o r and a 150 o h m r e s i s t o r in s e r i e s w ith the
g r o u n d t e r m in a l.
T h e c i r c u i t d e s c r i p t i o n a p p e a r in g in the T S -8 9 s e r v i c e
m a n u a l a p p lie s to the T S -1 7 2 c h a s s i s w ith the fo llo w in g e x
c e p t io n s :
1.
C - 1 7 , the R F to m i x e r c o u p lin g c o n d e n s e r , is 6 m m f i n
s te a d o f 8 m m f.
2.
In s o m e s e t s , V - 6 (6 A L 5 ) the v id e o d e t e c t o r , is r e p la c e d
b y a 1N60 g e r m a n iu m c r y s t a l .
3.
C a p a c it o r C -4 1 and r e s i s t o r R - 3 2 , a p a r t o f the c a th o d e
c o m p e n s a t in g n e t w o r k on the T S -8 9 , b e tw e e n the g r o u n d end
o f the c o n t r a s t c o n t r o l and the lo w e s t tap^have b e e n r e m o v e d .
L - 1 7 is c h a n g e d to a r e d - g r e e n d ot c o i l .
4 .
In s o m e s e t s , a 6 C B 6 tu be i s su b s titu te d f o r the 6A H 6 in
the v id e o a m p li f i e r sta g e ( V - 7 ) . T h e s c r e e n r e s i s t o r , R -3 5
c h a n g e s f r o m
33K to 22K w ith th is s u b s titu tio n .
su b s titu tio n f o r the 6A H 6 i s a 6 B C 5 .
R - 3 5 is c h a n g e d to 22K w ith th is s u b s t itu tio n a l s o .
5.
A n
a d d itio n a l
R C
n e t w o r k , c o n s is t in g o f R -1 0 0 (4 7 0 K )
and C -9 2 (100 m m f) h a s b e e n ad d ed in the c l ip p e r input c i r
c u it .
T h is n e tw o r k , w h ic h h a s a s h o r t t im e c o n s t a n t, h e lp s
to m in im iz e the e f f e c t o f n o is e p u ls e s at the c l ip p e r g r id .
I
6.
In s o m e s e t s , a 6SN7 tube is s u b s titu te d f o r the 12AU7
v e r t i c a l s w e e p g e n e r a t o r (V -1 3 ).
g r id r e s i s t o r ,
R - 6 3 ,
c h a n g e s f r o m
s u b s titu tio n .
7.
In s o m e s e t s a 6A S5 tube is s u b stitu te d f o r the 6W 6 v e r
t i c a l outp ut tu b e .
N o c o m p o n e n t c h a n g e s a r e r e q u ir e d w ith
th is s u b s titu tio n .
8.
In s o m e s e t s a 6H6 tu be is s u b stitu te d f o r the 6 A L 5 h o r
iz o n ta l p h a s e d e t e c t o r V -1 5 . N o c o m p o n e n t c h a n g e s a r e r e
q u ir e d w ith th is s u b s titu tio n .
9 .
T h e d a m p in g r e s i s t o r a c r o s s o s c i l l a t o r c o i l L - 4 E w a s
ch a n g e d f r o m 2200 o h m s to 3900 o h m s to s t a b iliz e the o s c i l
la t o r on the lo w c h a n n e ls .
10.
In
s o m e
s e t s ,
6A G 5
tu b e s in the f i r s t and s e c o n d IF a m p lif ie r s t a g e s .
f i r s t IF c o i l , L -1 2 , the lo w f r e q u e n c y t r a p , L -1 5 , the s e c
ond IF c o i l , and L -1 4 , the h ig h f r e q u e n c y t r a p , a r e c h a n g e d
in v a lu e w ith th is s u b s titu tio n .
d a m p in g r e s i s t o r a c r o s s T - l , c h a n g e s f r o m 6800 o h m s to
10
In the c a s e o f
CIRCUIT DESCRIPTION
A n o th e r
T h e s c r e e n r e s i s t o r
T h e s e c o n d m u lt iv ib r a t o r
330K to. 100K w ith th is
tu b e s a r e s u b s titu te d f o r 6AU 6
L - l l , the
S ee p a r ts l i s t .
R -1 3 ,
the
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2.
F r o m
c a th o d e o f p ic t u r e tube to c h a s s i s c o n n e c t a c a l i
b r a t e d o s c i l l o s c o p e .
N O T E :
T o c a l ib r a t e s c o p e , c o n n e c t it a c r o s s 6 .3 v o lt f i l a
m e n t su p p ly . T h e p e a k - t o - p e a k a m p litu d e on the s c r e e n w ill
then b e a p p r o x im a t e ly 18V (6 . 3 x 2 . 8).
3.
S et c o n t r a s t c o n t r o l f o r m a x im u m s e n s it i v i t y .
4 .
T u n e s ig n a l g e n e r a t o r to the v i d e o c a r r i e r fr e q u e n c y o f
the c h a n n e l b e in g c h e c k e d .
G e n e r a t o r s ig n a l s h o u ld be 30%
m o d u la te d at 400 c y c l e s .
T h e s ig n a l f r o m the g e n e r a t o r to
p r o d u c e 20 v o lt s p e a k - t o - p e a k at p ic t u r e tube c a t h o d e sh o u ld
b e l e s s than 25 m i c r o v o l t s on c h a n n e ls 2 to 6 and l e s s than
75 m i c r o v o l t s on c h a n n e ls 7 to 13.
4 7 0 0 o h m s .
R -1 4 ,
the f i r s t IF s ta g e c a t h o d e r e s i s t o r , is
b y p a s s e d w ith a 1500 m m f c a p a c it o r and R -1 4 and R -1 9 , the
s e c o n d
IF
sta g e
c a th o d e
r e s i s t o r , c h a n g e
o h m s w ith th is s u b s titu tio n .
11.
In s o m e s e t s , a 6A G 5 is s u b s titu te d f o r the 6A U 6 in the
a u d io d r i v e r - l i m i t e r s t a g e .
and r e q u i r e s no c i r c u i t o r c o m p o n e n t
s u b s t itu tio n
o f on e f o r the o t h e r in the f i e l d r e q u i r e s r e
t o u c h in g the a lig n m e n t o f the p r i m a r y o f the d i s c r i m i n a t o r
t r a n s f o r m e r f o r b e s t p e r f o r m a n c e .
12.
R -1 5 , R - 2 0 , C - 2 4 , and
R -1 9 , the c a th o d e r e s i s t o r s f o r V - 3 and V - 4 , a r e g r o u n d e d
d i r e c t l y .
T h e s u p p r e s s o r s a r e a ls o g r o u n d e d .
13.
T h e v id e o a m p lif ie r B p lu s s u p p ly w a s c h a n g e d f r o m
the 240 v o lt bu s to the 265 v o lt bu s and the a u d io a m p lif i e r
B p lu s s u p p ly w a s c h a n g e d f r o m the 265 v o lt bu s to the 310
v o lt b u s . T h e b o o t s t r a p c a p a c i t o r C - 8 3 , w h ic h w a s c o n n e c t
ed to the 240 v o lt b u s is now c o n n e c t e d to the 310 v o lt b u s .
14.
In la t e r s e t s , the h o r iz o n t a l outp ut tu be s c r e e n r e s i s t o r
R - 9 4 , is r e tu r n e d to the lo a d s id e o f the fu s e F - l .
15.
It h a s
b e e n
fou n d
that
r a i s e the " B " v o lt a g e 35 to 45 v o lt s t o o h ig h .
a f fo r d
a m e a s u r e
o f
p r o t e c t i o n f o r the 6 B Q 6 and 6W 4 in
th e s e in s t a n c e s , a r e s i s t o r R -1 0 4 h a s b e e n p la c e d in s e r i e s
w ith the s p e a k e r fie ld .
T h is c o n d itio n a r i s e s o n ly w ith c e r t a i n is s u e " O " , " A " ,
o r
" B "
t r a n s f o r m e r s
( is s u e
n u m b e r s ta m p e d on t r a n s f o r m e r s ) . In is s u e " C " t r a n s f o r m
e r s , w h ic h a r e c u r r e n t ly b e in g p r o d u c e d , th is d iffic u lt y h a s
b e e n r e m e d ie d and the r e s i s t o r is no lo n g e r n e c e s s a r y .
In fu tu re r e p la c e m e n t s o f t r a n s f o r m e r s , a c h e c k sh o u ld
b e
m a d e
o f
" B " v o lt a g e .
If it is fou n d to be lo w a ft e r the
new t r a n s f o r m e r h a s b e e n in s t a lle d ,
m e n tio n e d a b o v e .
If " B " v o lt a g e is fou n d to b e h ig h e r than
n o r m a l, i n s e r t c o r r e c t R -1 0 4 r e s i s t o r in s e r i e s w ith s p e a k
e r
fi e ld , a s
sh ow n
in
s c h e m a t ic
n u m b e r s f o r t h e s e
r e s i s t o r s
M E N T P A R T S L IS T .
T h e
tube
s u b s titu tio n s
w e r e n e c e s s a r y b e c a u s e o f the
c r i t i c a l s h o r t a g e in s o m e tube t y p e s .
d o not a f fe c t the o p e r a t io n o r c i r c u i t t h e o r y .
f r o m
47 to 56
T h is is an e x a c t r e p la c e m e n t
c h a n g e s ;
h o w e v e r ,
C -2 9
a r e r e m o v e d .
R -1 4 and
c e r t a in
p o w e r t r a n s f o r m e r s
In o r d e r to
d e s ig n a t io n f o l lo w s the p a r t
r e m o v e the r e s i s t o r
d ia g r a m .
C o r r e c t p a r t
w i ll be fou n d in R E P L A C E
T h e s e s u b s titu tio n s
)
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