Advertisement
7.
T u n e the h ig h fr e q u e n c y t r a p L -1 2 lo c a t e d on the 1st IF
c o i l f o r m a x im u m a tte n u a tion on the c u r v e at 27 . 3 m e .
8.
A d ju s t the 1st IF c o i l , L - l l , to p la c e a 2 6 .6 m e m a r k e r
on the h ig h s id e o f the r e s p o n s e c u r v e 60% d ow n f r o m m a x
im u m r e s p o n s e .
S ee F ig u r e 6.
9 .
A d ju s t the 2nd IF c o i l , L - 1 5 , to p la c e a 22 . 7 m e m a r k e r
on the lo w s id e o f the r e s p o n s e c u r v e 6 0 d o wn f r o m m a x i
m u m r e s p o n s e .
10.
A d ju s t the 3 r d IF p la te t r a n s f o r m e r T - 2 to p r o v id e a
fla t to p o r s y m m e t r i c a l r e s p o n s e c u r v e .
11.
R e s e t the t r a p s (s t e p s 6 and 7) and a g a in c h e c k the IF
f o r p r o p e r r e s p o n s e .
N O T E : It i s s u g g e s t e d that the b ia s b e r e m o v e d f o r a c c u r a t e
s e ttin g o f the t r a p s .
12.
W ith b ia s a p p lie d , c o n n e c t the s w e e p b e tw e e n the g r id
(p in 2) o f the m i x e r tube V - 2 A (1 2 A T 7 ) and c h a s s i s .
13.
D is c o n n e c t
the
t r i m m e r ,
g r id o f the m i x e r tu b e, o r s h o r t the t r i m m e r th ru a 1 0 ,0 0 0
m m f c e r a m i c d i s c typ e to c h a s s i s .
14.
B r in g b o th c o r e s o f the m ix e r t r a n s f o r m e r , T - l ,
m u lt a n e o u s ly
f r o m
the
o u ts id e
h a lf-w a y m a r k e r s s h o u ld be 2 6 .4 m e and 2 2 .9 m e .
N O T E :
In a lig n in g the th r e e IF c o i l s , e a c h c o i l is a d ju s te d
in d iv id u a lly , but w h en a d ju stin g the p r i m a r y and s e c o n d a r y
o f the m i x e r t r a n s f o r m e r , the a d ju s t m e n ts sh o u ld b e m a d e
s im u lt a n e o u s ly .
T h e im p o r ta n t p o in t to k e e p in m in d is to
o b ta in a fla t r e s p o n s e c u r v e w ith a s m u c h g a in as p o s s i b l e .
T h e
s id e s
o f
the c u r v e sh o u ld b e s t r a ig h t and as s t e e p as
p o s s i b l e .
S im u lta n e o u s a d ju s tin g o f the p r i m a r y and s e c
o n d a r y is the e a s i e s t w a y to o b ta in th is r e s u lt .
f o r m e r b y i t s e l f i s , in e f f e c t , tuned f o r the s a m e p a s s band
as
the
t h r e e
s t a g g e r e d c i r c u i t s .
d i f f e r e n c e in the o v e r a l l w a v e f o r m sh o u ld b e that the s id e s
o f
the
o v e r a l l w a v e a r e s t e e p e r .
m a r k e r s
(2 2 . 9
m e
and
26. 4
s in c e it is a b s o lu t e ly n e c e s s a r y to o b ta in the p r o p e r c u r v e .
A s lig h t d ip (n ot e x c e e d in g 10% ) is p e r m i s s i b l e in the m ix e r
t r a n s f o r m e r r e s p o n s e c u r v e .
B A N D W ID T H
T h e b a n d w id th m a y b e d e t e r m in e d b y c o n n e c t in g an A M
g e n e r a t o r to the m ix e r g r id .
at 24. 6 m e , a d ju s t the output f o r 1 v o lt r e a d in g on a V T V M
c o n n e c t e d
to
p in
4 o f t e s t s o c k e t and c h a s s i s .
output o f the g e n e r a t o r .
N ow b y tunin g e it h e r s id e o f 24. 6
m e
and
n o tin g
the
fr e q u e n c i e s
r e a d s 1 v o lt , the 6 db b a n d w idth p o in ts a r e in d ic a t e d .
p o in ts
s h o u ld
b e
2 2 .9
m e and 26. 4 m e .
m e t e r w h ile tunin g s lo w ly th ru the band any s e r io u s p e a k s
o r h o l e s in the r e s p o n s e c a n a ls o b e d e t e c t e d .
R E G E N E R A T IO N C H E C K
A ft e r the a b o v e IF and m ix e r t r a n s f o r m e r a lig n m e n t h a s
b e e n
m a d e , a
c h e c k
f o r
r e g e n e r a t io n in the IF a m p lif ie r
s t r ip sh o u ld be m a d e . T h is is d o n e b y r e m o v in g the b a tt e r y
b ia s and o b s e r v i n g the output r e s p o n s e c u r v e on the o s c i l l o
s c o p e , as tak en b e tw e e n the p ic t u r e tube c a th o d e and c h a s
s i s .
T h e ba n d w id th m a y c h a n g e w ith the b ia s r e m o v e d but
sh ou ld not ch a n g e m o r e than 0. 2 m e .
t r o l to m a x im u m g a in .
D e c r e a s e the input u n til the output
s ig n a l sh o w s a m a r k e d d e c r e a s e .
C - 1 4 ,
in L C c i r c u i t in the
s i
t o w a r d s the c e n t e r .
T h e
T h e t r a n s
S ee F ig u r e 7.
T h e o n ly
C o n sta n t u s e o f the 50%
m e )
sh o u ld b e r e s o r t e d to ,
W ith the g e n e r a t o r f r e q u e n c y
D ou b le the
at w h ic h the V T V M a g a in
T h e s e
B y w a tc h in g the
S et the c o n t r a s t c o n
A n y r e g e n e r a t io n p r e s e n t
Scanned by mbear2k - Jan 2012
w ill
be
in d ic a t e d b y s h a r p p e a k s on the o v e r a l l r e s p o n s e
c u r v e .
T h e
o s c i l l a t o r
s h o u ld
a b o v e , d u r in g th is p r o c e d u r e .
C A U T IO N :
D o not in je c t t o o m u c h m a r k e r s ig n a l.
M IX E R L C A D J U S T M E N T
R e c o n n e c t b ia s r e m o v e d f o r r e g e n e r a t io n c h e c k .
p la c e t r im m e r C -1 4 in L C c i r c u i t o f m ix e r g r id o r r e m o v e
10, 000 m m f c e r a m i c b e tw e e n t r i m m e r and c h a s s i s .
the t r i m m e r s o it is tuned to the c e n t e r o f the m ix e r r e
s p o n s e c u r v e .
T h is is in d ic a t e d b y o b s e r v in g the e f f e c t o f
the L C c i r c u i t on the m i x e r r e s p o n s e .
p a c it y
o f
the
t r im m e r
and
a b o v e the IF r a n g e in to the IF r a n g e , it w i l l be n o te d that
the m ix e r c u r v e w ill p u ll d ow n on the h ig h s i d e , s t r a ig h t e n
out as the L C c i r c u i t a p p r o a c h e s the m id d le o f the r a n g e ,
and p u ll d ow n on the lo w s id e as the L C c i r c u i t a p p r o a c h e s
the
lo w
end
o f
IF
r a n g e .
p o in t at w h ic h the m i x e r c u r v e s t r a ig h t e n s ou t.
the L C c i r c u i t is s i m i l a r to a ja c k c o i l w h en it is w ith in the
IF r a n g e .
C A U T IO N :
T u n in g the L C c i r c u i t v e r y lo w w il
o s c i l l a t i o n .
IF S E N S IT IV IT Y M E A S U R E M E N T S
IF S ta g e s O n ly
1.
R e m o v e the b a t t e r y b ia s f r o m 1st IF tu b e g r id .
2.
C o n n e c t an A M
s ig n a l g e n e r a t o r , s e t at 24. 6 m e , th ru
a b lo c k in g c a p a c it o r o f 5000 m m f, b e tw e e n c h a s s i s and the
g r .d (p in 1) o f the 1st IF tube V - 3 .
3.
C o n n e c t an e l e c t r o n i c v o lt m e t e r a c r o s s the v id e o d e t e c
t o r lo a d r e s i s t o r R - 2 8 (5 6 0 0 ).
sh o u ld be d e c o u p le d w ith 100K o h m r e s i s t o r s .
4 .
5iet the 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 iv it y .
5.
Stop the
o s c i l l a t o r tube b y d is c o n n e c t in g r e s i s t o r R - 9
(1500) f r o m the p la te (p in 6) o f t u b e V - 2 B (1 2 A T 7 ) o r b y s u b
stitu tin g a n o th e r tube w ith p in 6 r e m o v e d .
6.
T h e s ig n a l r e q u ir e d to p r o d u c e
c o n t a c t p o te n tia l on the m e t e r sh o u ld be l e s s than 700 m i c r o
v o lt s .
M ix e r & IF S ta g e s
T h e p r e li m in a r y p r e p a r a t io n s a r e the s a m e a s f o r c h e c k
ing the s e n s i t iv it y o f the IF s t a g e s e x c e p t :
1.
C o n n e c t the A M s ig n a l g e n e r a t o r , s e t at 24. 6 m e , th ru
a 5000 m m f c a p a c i t o r , b e tw e e n c h a s s i s and the g r id (p in 2)
r i the m ix e r tube V - 2 A (1 2 A T 7 ).
2.
T h e
s ig n a l
r e q u ir e d to p r o d u c e 1 v o lt (n e g a t iv e ) a b o v e
c o n t a c t p o te n tia l on the m e t e r s h o u ld be l e s s than 125 m i c r o
v o lt s .
O S C I L L A T O R , A N T E N N A A N D R F A L IG N M E N T
N O T E :
T h e IF m u s t be a lig n e d b e f o r e the R F s e c t io n c a n
be p r o p e r l y p h a s e d .
E q u ip m e n t R e q u ir e d :
S w e e p G e n e r a t o r : F r e q u e n c y r a n g e 4 0 -2 2 0 m e ; 10 m e s w e e p
b e
s t o p p e d ,
a s
d e s c r i b e d
R e
A d ju s t
I n c r e a s in g the c a
b r in g in g the L C c i r c u i t f r o m
T h e p r o p e r tunin g p o in t is that
In e f f e c t ,
c a u s e
B o th le a d s f r o m the m e t e r
1 v o lt (n e g a t iv e ) a b o v e
7
Advertisement
