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MA 1a. MA 1a
is the designation of a slight modification of MA 1 which has a slightly
different operational characteristic. The MA 1a circuit is identical with
that of MA 1, as shown in figure 200, with the
exception that in MA 1a, R9 has a value of 10 M Ohms
in-stead of 1 M Ohm. The result is that during the live cycle (45 seconds)
of the acoustic component after triggering, the acoustic sensitivity falls
off quite rapidly after reaching its peak within 1 to 2 seconds after
triggering, firgure 201a. Thus, if the acoustic
influ-ence does not occur immediately after triggering influence is
necessary to fire the mine. This is designed to make sweeping more
difficult. Increasing the value of R9 to 10 M ohms has
the effect of isolating the screen grid of V from its battery connection. At
the start of the cycle, C8 is fully charged to 45
volts. However, when V is energized, the screen grid as well as the plate
start drawing current, with the result that C8 is at
least partially discharged. The resultant lowering of the screen potential
inhibits the pentode characteristic of V, and it tends to approach a triode
characteristic. Thus, for the same E and Eg the plate current Ip is lower
and a much higher sound level is necessary to fire the mine,
figure 201b. The MA 1 circuit has a tendency to show
this characteristic, but it is not as marked as in MA 1a and does not
seriously affect its sweepability. |
