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T T S 26B
Section 4
b.
T W D - L
in ON
HK
position, applies
a ground to the M jack and the
M
l e a d o r
ring of the
LINE
jack.
c .
TWD-D in O F F HK position, applies
a ground to the
E lead o r tip of the D R O P
jack.
d .
TWD -D in O N HK position applies an
open to the E lead o r tip of the DROP jack.
4 . 3 1 DIALING AND TALKING FUNCTIONS.
4. 32 A l i n e m a n ' s telephone s e t o r a s u b s c r i b e r ' s
s e t m a y b e connected to the EXT DIAL jack o r
binding p o s t s to d i a l out o r talk on a loop o r E & M
s u p e r vised c i r c u i t .
The dialing functions have
a l r e a d y b e e n reviewed in p a r a g r a p h s 4 . 1 7 , 4 . 2 1 ,
and 4 . 2 2 .
4.33
When the
EXT
DIAL CIRCUIT s w i t c h is s e t
a t TALK E M o r TALK R T , the EXT DIAL jack
and binding posts a r e connected to the t i p and
ring of the SEND 1 and 2 jacks a s follows:
a.
TALK EM: The sending c i r c u i t i s con-
nected to the EXT
DIAL
jack through
2pF
blocking c a p a c i t o r s
,
and battery is applied
through 50052 to the ring of the jack, and
the t i p i s connected to ground through 500Q.
T h i s provides b a t t e r y for talking on a d r y
c i r c u i t .
b.
TALK RT: T h e sending c i r c u i t is con-
nected d i r e c t l y to the
EXT
DIAL jack to
p e r m i t talking on a loop o r wet c i r c u i t .
4 . 3 4
OSCILLATOR-BUFFER AMPLIFIER.
4. 35 The oscillator-buffer amplifier c i r c u i t r y
contained within the Model TTS 26B P u l s e Sig-
naling T e s t Set is normally equipped to o p e r a t e
on any of the following frequencies: 4 , 6 , 8 , l O , 12,
1 4 ,
o r
20 c p s ; an additional frequency c a n be
+stalled
on
s p e c i a l o r d e r .
The purpose of the
o s c i l l a t o r - b u f f e r c i r c u i t r y is to provide a n output
sine wave to o p e r a t e the DRIVE r e l a y .
T h i s c i r -
cuit is contained o n
a
printed board which i s
mounted a s a s u b unit on the main component
board.
4.36
The output s i n e wave of this unit i s coupled
to the DRIVE r e l a y when the SEND and T E S T key
switch is i n the OSC position.
Through the adjyst-
m e n t of the ADJ
O/o BREAK
control, a s s o c i a t e d with
the DRIVE r e l a y , the point on this s i n e wave at
which the DRIVE r e l a y will o p e r a t e c a n be v a r i e d
thus the adjustable
Q/o
b r e a k is achieved.
4. 37
As t r a n s i s t o r i z e d c i r c u i t s a r e used
,
no
e x t e r n a l power other than the 48-volt station
b a t t e r y i s r e q u i r e d ; no w a r m - u p period is required
f o r this unit.
T h e
operation of t h i s c i r c u i t i s
a s follows:
4.38 The c i r c u i t d i a g r a m to which the following
d e s c r i p t i o n applies is shown i n fig.
5 .
1 .
The
location of the component p a r t of this c i r c u i t is
s h o w n i n f i g . 5 . 2 .
,
4.
39
A bridged-T type of
R - C
o s c i l l a t o r , con-
sisting of t h r e e t r a n s i s t o r s t a g e s , i s used.
The
f i r s t two t r a n s i s t o r s a r e d i r e c t l y coupled f r o m
the collector of Q1 to the b a s e of Q2.
The posi-
tive feedback path i s completed f r o m the e m i t t e r
of Q2 back through a blocking c a p a c i t o r , C2,
and a tungsten l a m p , R89, utilized f o r l e v e l
stabilization, to the e m i t t e r of Q1.
A p a r t of the
e m i t t e r r e s i s t a n c e , R15, of Q1 h a s been made
v a r i a b l e to allow setting the c o r r e c t amount of
positive feedback n e c e s s a r y f o r s t a b l e operation.
4.40
A negative feedback, which i s g r e a t e r than
the positive feedback, i s supplied to the base of
Q1 through a null s e l e c t i v e network and an
e m i t t e r follower, Q3
At i t s tuned frequency,
the s e l e c t i v e bridged- T null network d e c r e a s e s
.
the negative feedback sufficiently to p e r m i t
oscillation to o c c u r at the d e s i r e d frequency,
which i s determined by the R - C values employed
within the network.
T h i s frequency -de termining
network c o n s i s t s of two c a p a c i t o r s ,
C4
and C5,
and two selected value r e s i s t o r s .
4 . 4 1 Amplifier s t a g e Q4 and the c a s c a d e e m i t t e r
follower s t a g e s , Q5 and Q6, provide the n e c e s -
s a r y voltage and c u r r e n t gain r e q u i r e d to o p e r a t e
the
DRIVE
r e l a y .
The output l e v e l of the amp-
l i f i e r s t a g e i s d e t e r m i n e d by the setting of
potentiometer R19.
Capacitor C7 provides
DC
blocking between the output e m i t t e r follower Q6
and the d r i v e n coil of the DRIVE r e l a y .
4.42
P u l s e Speed Measuring C i r c u i t .
4 . 4 3 When the METER CIRCUIT switch, S8, i s
i n the 0-25
PPS
position, a voltage directly
proportional to the frequency of the signals
r e c e i v e d is g e n e r a t e d by this p u l s e speed m e a -
s u r i n g c i r c u i t .
T h i s voltage is coupled to the
m e t e r , thus allowing d i r e c t r e a d i n g of the speed
of the signals a s r e c e i v e d by t h e s e t .
4 . 4 4
The operation of this c i r c u i t is a s follows.
When the METER CIRCUIT switch i s i n the 0-25
PPS
position, the r e c e i v e c i r c u i t s a r e coupled to the coil
of r e l a y K4. Thus K4 will follow the pulses received
When
K4
is i n the r e l e a s e d condition, c a p a c i t o r C12
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