IBM 01 Maintenance Manual page 414

ATTACHMENTS CUSTOMER ENGINEERING
Electronic Tab "osition
Fig. 9. Armature Interlock Mechanism
12. RIGHT HAND FINAL STOP
The right hand final stop can be adjusted up or down
through the elongated mounting hole. The inside nut on
the right end of the tab rack holds the stop in place
(Figure 8). The upright portion of the tab check lever
should strike the left end of the stop whenever the car-
riage is moved to the extreme left. The stop should not
interfere with other carriage or rear rail parts.
8ectronic Tab Circuit
The electronic tabulation circuit consists of an on/off (
switch, a transformer, a Type 2D21 thyratron, a sensing
finger and contact plate, a magnet and a contact which
operates in conjunction with the tab lever.
When the tab key is depressed the tab lever contact
is closed as the tab lever is latched out. This completes
the anode circuit of the thyratron amplifier. The thyratron
is prevented from conducting at this time, however, be-
cause the No. 1 grid is at minus potential with respect
to
the cathode.
At the same time that the tab lever contact is being
closed, the sensing finger is raised into the upper position
closing the sensing finger contacts. As a conductive line
passes under the sensing wires it completes the circuit (
and changes the potential on the No.1 grid to plus with
respect to the cathode. As the No. 2 grid is at cathode
potential at all times the thyratron now conducts and
picks the magnet, releasing the tab check and rebound
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