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70
T Y P E
6 0 3
E L E C T R O N I C M U L T I P L I E R
sistors must be used.
The values given above are
cause improper operation of triggers. T o eliminate
approximate.
If a tube is to be maintained in a conductive
state, its grid is connected to a high positive poten-
tial through a high value resistor.
The grid cur-
rent flowing through the grid resistor will reduce
the grid ~ o t e n t i a l to the ca,thode potential.
Any
tendency of the tube current to drop will be ac-
companied by a reduction in grid current, hence
the grid potential will rise and overcome the ten-
dency of the tube current t o drop.
This method
of connecting the grid in normally conducting
tubes overcomes any difficulty which is due to var-
iations in individual rubes. All normally conduct-
ing tubes are indicated on the wiring diagram by
placing an
X
under the cathode symbol.
I n many parallel arrangements, grid resistors are
used to prevent parasitic oscillatiotzs. A parasitic
oscillation is any undesirable oscillation in a circuir
which interferes with its normal operation, or
lowers its efficiency. Parasitics may result from a
momentary fluctuation of current through a tube
which causes grid porentials on other tubes to
change. This would cause current through these
other tubes t o change, which in turn changes the
potential on the grids of the first tube, and creates
a con,tinuous interaction or oscillation. By placing
resistors in the grid circuits, the effect of potential
variations in one tube on the grid of another is de-
creased to a point where interaction is eliminared.
A n example of parasitic suppressing resistors is
shown on the circuits for the C and
D
chassis. O n
the C chassis (Section
3 1 )
the suppressors of six
6SK7's are in parallel, while the
D
chassis (Section
3 4 )
shows six g i d s in parallel.
By-pass capacitors are also used in many cases
throughout the computing section to prevent un-
desirable effects by tm?zsie~zt z~oltages. Transient
voltages are very rapid voltage changes resulting
from load changes, fluctuation in supply voltage
arcs resulting from breaking inductive circuirs, etc.
Transients can cause parasitic oscillations if pro-
per precautions are not taken. Also transients can
possible transients caused by arcs, extreme care
must be exercised to eliminate all arcs in the punch
unit.
The trouble resulting from arcing at H D 1 relay
points may be used as an example. Although these
points in the motor circuit are on the shielded side
of the transformer, a heavy arc across its points
will cause the product counter read-out trigger to
operate and add 1's in the product counter.
O f
course this will happen only when the motor is
being started.
This trouble was eliminated by
suppressing the arc with a
2
mfd capacitor across
the H D 1 points.
Transient voltage pulses may be transferred
from one circuit to another by capacity coupling
between wires in a cable. T o minimize this possi-
bility, all high-speed pulses
raveli in^
from one
chassis to another not adjacent to it are carried by
shielded cable.
A n example of by-pass capacitors used t o elim-
inate trouble from transients can be found in the
circuit for the C chassis (Section
3 1 ) .
The
.OT
mfd capacitors at the input t o the read-in triggers
are by-passes for transients.
All resistor values are shown on the circuit in
~rzegoh~rrs. All capacitor values, shown as zvhole
~zz~t~zbers,
are in micro-microfarads, while capacitor
values shown as deci~nals are in microfarads.
All tubular capacitors and wire-wound resistors
are stamped with their value. However, the value
of molded mica capacitors and carbon resistors is
indicated by color code only.
The code used is
shown in Figure 66.
As an example, a resistor with a yellow stripe on
the end, followed by a violet stripe, another yellow
stripe, and a gold stripe will have a resistance of
470,000
ohms, and the value will be within
-t
5
%.
For another example, assume a molded mica capac-
itor with a yellow dot at the upper left, followed
by two black dots. The lower left has a green dot
followed by a red dot and a gold dot. This code
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