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E L E C T R I C A L
P R I N C I P L E S
103
of the anode resistors in the switch tube anode cir-
cuit. Since only one circuit is in operation at the
time, this permits simpler connections as only one
counter input wire is required for both operations.
The multiplicand counter consists of six elec-
tronic counter positions on chassis I,
J,
and K,
shown on Sections 43 through 48 of the wiring
diagram. All counter positions are exactly the
same; therefore, no effort will be made to repeat
any counter operations.
The screen potential of the multiplicand read-in
switches is under control of the factor reversal
switch.
When set for group multiplying, with
the factor reversal switch
ON,
the screen supply is
open on all cards except the rate card; the switch
tubes are non-conductive.
Observe that the
+
65
volt supply on the
D
chassis is connected to
terminal CNp34. This connection places the
+
65
volt supply for the multiplicand read-in switches
under the control of the group multiply and fac-
tor reversal relays.
The read-in controls for the multiplier counter
appear on chassis C and circuits are shown in Sec-
tions 31 and 32. The multiplier read-in switches
also have their screen supply connected through
the group multiply and factor reversal relays in
the punch unit through connector CNp32. This
arrangement is used to permit conduction by the
read-in switches only when a rate card passes the
first set of brushes during a group multiplying
run. Use is made of the fact that a 6SK7 will not
conduct if there is no potential on its screen. The
multiplier counter (chassis
E,
F,
G )
circuits are
shown in Sections 35 through 40. Figure 98 is a
block diagram of all read-in circuits, showing all
tubes for all counter positions.
COMPUTING CIRCUITS
Multivibrator and Clippers
After the multiplier and multiplicand factors
have been entered into their respective counters,
the operation of the computing section is initiated
by P24 cam contact at I
I
.5 on the index. Before
explaining the starting of computations in petail,
means of producing operating pulses for the com-
pu,ting section will be described.
A suitable oscillator is required as a parent
source of pulses for performing the computations.
The pulses must be square wave pulses for proper
operation of triggers; consequently, a multivibra-
tor type of oscillator is used.
The multivibrator
develops roughly square-topped waves of potential
at the outputs of the two tubes, the waves at one
output being 180" displaced in phase from those
on the other output. In this machine two multi-
vibrators are provided, one to generate square
waves at approximately 3 5,000 per second for nor-
mal computations and one to generate 5 cycles per
second for slow-speed operation, which permits
visual observation of tube operations by watching
the indicator lights. A dial switch is provided to
switch from one multivibrator to the other.
Fluctuations in the frequency of the multi-
vibrator do not affect the accuracy of the comput-
ing operations since the multivibrator is itself the
master timer of all computing operations.
As the output of the multivibrator is not a true
square wave, some means must be provided to
shape the pulse into a square wave. This is done
by means of clippers, which utilize only a portion
of the wave from the multivibrator and thus pro-
duce an almost perfect square wave. The theory
of operation of both multivibrators and clippers
follows.
Thorough knowledge of the theory of
operation of multivibrators and clippers is not es-
Figure 99. Basic Form o f Multivibrator
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