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72
SPECIAL
DEVICES
circuits described in the Type 82 circuit description
section of this manual.
Static Circuit Conditions
A 2D21 thyratron tube (master card control) is
connected across the
DC
machine circuit with a 2000
ohm resistor in the cathode circuit and a high speed
relay in the anode circuit. Negative bias voltage for
this tube is obtained from the standard bias oscillator
and rectifier and is applied to the grid in series with
two 500K resistors, making the grid approximately
40 volts negative with respect to the cathode. This nega-
tive bias prevents the tube from firing when anode vol-
tage is applied each cycle at the time commutator 2
makes.
The control grid of the tube is also connected to the
master rail brush through a .05 mfd capacitor.
Firing the MCC Tube
Shortly before a master card reaches the card brush
station, the rail brush senses a corner cut in the lead-
ing edge of the card (Figure 51). This applies a posi-
tive pulse to the control grid of the master card control
tube through commutator 2, the master rail brush, the
. 05 mfd capacitor, and the 500K resistor. This positive
voltage cancels the negative grid bias and causes the
tube to fire since, at this time, anode voltage is also
applied to the tube through commutator 2.
Firing of the MCC tube picks up the MC relay in
the anode circuit, thus transferring the MCR points.
Opening of the
N / C
MCR point allows removal of the
anode voltage from all impulse storage tubes when com-
mutator 3 breaks. This allows any storage tube (12
through 9) which has been previously fired to de-ionize,
thus clearing the impulse storage section.
Closing of the
N / 0
MCR point completes a circuit
as follows: from the positive side of the line, through
contact roll cover switch 1, the card lever contacts,
group sort switch 1, to commutator 2, commutator 3,
through A-3, MCR
N/O,
A-2, to the outer brush
on the selecting commutator. This permits placing
a positive potential on the contact roll when the
inner brush sweeps across the segments, thus allowing
the card brush to sense holes in the master card.
Just before 9 time at the start of the master card
cycle, the center and outer selector commutator brushes
make. This happens before commutator 2 breaks at
-h"
before 9. In conjunction with the MCR
N/O
point,
these brushes shunt around commutator 2, thus main-
taining a positive potential on the anode of the MCC
tube and keeping the MC relay energized until the end
of the master card cycle when the center brush breaks.
Commutator 3 makes at
3 5 2"
before 9, shunting the
N/C
MCR point (now open) and applying anode volt-
age to the impulse storage tubes.
Sorting the Master Card
When the card brush senses a hole in the master
card, the full
DC
machine circuit voltage is applied to
the starting anode of the OA4G trigger tube. This
c;:auses immediate firing of the OA4G and sorting of
the master card into the corresponding pocket. At the
same time, this positive voltage is applied through the
corresponding impulse emitter segment to a tube in
the impulse storage section.
Each impulse storage tube (2D21 thyratron) is con-
nected across the
DC
circuit with a 47K resistor in
series with its cathode. Negative grid bias for these tubes
is obtained in the same manner as for the MCC tube.
The positive pulse from the impulse emitter segment
is applied through a .05 mfd capacitor and a 500K
resistor to the control grid of the storage tube con-
nected to that emitter segment. This voltage cancels
the negative grid bias on the tube, causing it to fire .
Once fired by the action of a master card, the tube re-
mains in conduction until the following master card
(or a trailer card) is sensed. Since the voltage drop
across a conducting 2D21 is approximately 8 volts, the
voltage on the cathode of the storage tube during con-
duction rises almost to the full
DC
circuit potential. The
majority of the potential drop appears across the 47K
resistor in the cathode circuit.
At the end of the master card cycle, the center brush
on the selecting commutator breaks, de-ionizing the
MCC tube and dropping out the MC relay. The
N/C
MCR points close before commutator 3 breaks, thus
maintaining anode voltage on the impulse storage tubes
and keeping that tube in conduction that was pre-
viously fired by punching sensed in the master card.
The
N/O
MCR point breaks the circuit to the selecting
commutator and the contact roll to prevent sensing of
detail card information by the card brush.
Sorting Detail Cards
If the card immediately following the master card is
a detail card, it will not be read by the sort brush
because of the condition of the
N/O
MCR point. How-
ever, when the impulse distributor makes on the seg-
ment corresponding to the value sensed in the previous
master card, a positive potential is applied to the Start-
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