CIRCUIT
DESCRIPTION
31
ohm resistor also serves
as
a protective device for the
25L6 power tubes
by
reducing the initial high surge
of current through these tubes to a value below their
safe maximum continuous rating. Thus, if the machine
were stopped at a time in the card
cycle
when the
power tubes were conducting, the continuous flow of
current through the tubes would not
be
great enough
to cause damage.
Restoring Bias
When
the hole in the card passes from under the
card brush, thus insulating the brush from the contact
roll, the positive voltage
is
removed from the OA4G
starter anode. This
does
not cause the OA4G tube
to
stop conducting, however, since the starter anode
loses
control of conduction in a gas tube after the tube
fires
(principle
9).
The OA4G continues
to
conduct until
the center brush on the commutator opens the anode
circuit.
When
this occurs, the OA4G
is
extinguished
and current
ceases
to
flow
through the 10,000 ohm
resistor. The voltage drop across this resistor
is
then
lost (principle
3),
and the control grids of the
25
L6
tubes and the cathode and starting anode of the OA4G
are returned to
40 to 45 volts negative bias
by
the
oscillator and rectifier circuit. Restoring bias
to
the
grids of the 25L6 tubes causes these tubes to cease
conducting, thus de-energizing the sort magnet.
Between the 12 position of the leading card and the
9 position of the following card, the armature return
spring and the armature knockoff come into play to
restore the armature
to
its normal raised position in
preparation for sorting the following card.
Miscellaneous
Components
The 47 ohm resistors in the screen grid circuits of
the 25L6 power tubes suppress parasitic oscillation
which may appear
as
a result of operating tubes in
parallel.
The
47,000 ohm resistors in the 25L6 control grid
circuits serve to limit the positive grid swing on con-
ducrion which would otherwise allow excessive grid
current to damage the tube. These resistors also act
as
isolating resistors to prevent the development of para-
sitic oscillations in these tubes.
The
.001 mfd. capacitor between the cathode and the
starting anode of the OA4G serves
to
by-pass transient
impulses which may be introduced into the card brush
circuit and cause
firing of the tube even though no
hole has been sensed in the card.
The
.05
mfd. and the 150 ohm resistor in series
between the cathode and the anode of the OA4G also
serve to by-pass transient impulses and prevent them
from firing the tube prematurely.
The
470K ohm resistor in the OA4G circuit connects
the starting anode to its cathode through the
10,000
ohm resistor, thus keeping the starter anode at its
own cathode potential whenever the card insulates the
card brush from the contact roll.
E Suffix
Changes
Machines wired
to
301701-E are similar in circuit
operation to machines which are wired to
30l701-C or
D.
On the E
suffix
wiring diagram, the 12SN7 rectifier
tube
is
replaced with a selenium rectifier. An additional
power tube
is
added in the circuit
to
the sort magnet.
This added power tube furnishes more current to the
sort magnet, thus increasing the safety factor of op-
eration. This
was
considered especially desirable for
DC-operated machines.
The E
suffix
electronic chassis consists of a flat plate
instead of the L-shaped chassis shown in Figures 22
and 23. The flat chassis
is
electrically interchangeable
with the L-shaped chassis if the machine
is
wired to
301701-D or 301701-C, or if the machine has been
altered in accordance with CEM 1213.
F Suffix
Changes
Machines wired
to
301701-F are similar in circuit
operation to those wired to
301701-C, D, or
E.
The
electronic chassis
is
physically and electrically the same
as
that
used
for 301701-E. A running light
is
in-
corporated in the circuit to indicate to the operator that
the machine
is
ready for operation. This light comes
on after the time delay relay picks up.
Machines wired
to
301701-F are Vinyl-covered ma-
chines and have several redesigned external features
which modernize the machine.
G Suffix
Change
Machines wired to 301701-G that operate on 115,
208, 230 volts AC, 50 or 60 cycle, obtain tube bias
voltage from a transformer which replaces the 25L6
oscillator
bias
circuit.
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