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E L E C T R I C A L
P R I N C I P L E S
77
Figure 73. Basic Eccles- Jordan Trigger Circuit
When the tube conduas, the
at point
tion of a trigger circuit will be ~resented. Although
A drops because of the
IR
drop across the load re-
a detailed knowledge of the theory of operation
sistor of the pentode.
In this case the output is
of a trigger is not necessary to repair rhe ma-
taken from a midpoint tap
M
on the load resistor.
chine, a thorough knowledge of the theory will
This would be done if the voltage shift desired is
assist in analyzing trigger troubles. A trigger cir-
only half the voltage shift at point A.
Assume
cuit is one which has two stares of equilibrium for
the potential a,t point A changes from $1 50 volts
to
+ Y O
volts. When conduction starts, a 100 volt
negative pulse is
at A. However,
a t
point
M
the poten~ial only changes from + I 50 volts to
+
100 volts, producing a 50 volt negative pulse at
M.
The screen grid in Figure 7 2 is shown at a fixed
potential of +65
volts supplied by
a
65 volt
screen voltage supply. The capacitor C across R I
is necessary t o balance the imerelectrode tube capa-
city so that the grid of the tube can follow the ap-
plied potential without any time delay.
TRIGGER CIRCUIT
fixed values of supply potential and circuit com-
ponents. The trigger circuit derives its name from
the fact that it can be made .to "trigger" abruptly
from one state of equilibrium to the other by
means of small controlling potentials. The trigger
circuit used in this machine is basically the Eccles-
Jordan trigger circuit shown in Figure 73.
The
use of this circuit is based on the fact that current
can flow through only one tube a.t
a
time.
A
change in grid potentials or anode potentials can
be made to transfer conduction abruptly from one
tube to the other.
As mentioned above, rhe trigger circuit is a de-
vice using two triode tubes so interconnected that
Theory of Operation
one tube is conducting while the other is non-con-
The most important and basic circuit used in the
ducting.
As shown in Figure
73
the grid of T 2
electronic computing section is the trigger circuit.
is coupled to The anode of T I through the coupling
For this reason a detailed analysis of the opera-
resistor Rc and capacitor C.
The !grid of TI is
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