Willmar tribune. [volume] (Willmar, Minn.) 1895-1931, 1922-07-19

grid, determine the value Of e. e is
the negative potential which must be
applied to the grid in order to reduce
the plate current to zero. The value
or +, which is the positive grid DOten-
tlal that will cause the maximum or
saturatlOn current to flow in the plate
circuit, is also determined by the rela-
tive position Of the grid with respect
TO the tilament and plate. If the grid
IS OF very fine mesh, the value of e
IS small because the electrons in pass
ing through the small mesh Of the
grid on their journey from the fila
ment to the plate will negatively
charge the grid and will be repelled
Similarly small positive charge ap-
piled to fine mesh will tend to ac-
celerate the velocity Of the electrons.
In case OF very coarse mesh grid,
the electrons can pass through the ap-
ertures in the grid without coming in
SO close to the charge on it and
relatively high potential will be re-
CURED on the grid to control the cleo
tron stream, or in other words. the
current flowing in the plate circuit.
Referring to Fig. VIII, O-G, is the
current that will flow in the plate cir
cult when there is no potential ap-
Piled to the grid. Suppose a positive
potential as OF is applied to the grid.
The corresponding plate circuit current
will be I'D or BID, more than it was
when the grid had no potential ap-
piled to it.
A negative potential Of OH IS now
applied to the grid where OH is vuuaI
in value to OF, but opposite in sign.
The application Of the negative pO-
tential when applied to the grid will
cause the plate current to be reduced
to, a value He or A-C, less than it
was when there was no potential an
piled to the grid. So 1t is seen that a
negative potential when applied to the
grid does not reduce the plate circuit
current as much as the same positive
potential increased the plate circuit
current. This irregular conductivity Of
the tube"is made use of when the tube
is used as detector or rectif1er Of
radio signals.
The incoming radio signal is a high
frequency alternating current. Let us
apply an alternating difference Of DO
tentlal whose maximum positive val
ue is equal to o. and whose maximum
negative value is equal to OH, to the
grid OF the three-electrode tube
whose characteristic curve is the same
as that shown in Fig. VIII. In Fig.
TX is shown the alternating difference
of potential applied to the grid
Through the first quarter Of cycle.
from zero at to maximum mega
tive value at X, equal to OH, the
plate: circuit current will vary from
O-G, it's value at P when no grid DO
tential is applied to a value at @ equal
to H-CA
During the next quarter of a cycle
the grid potential changes from
maximum negative value at X to zero
at. l.. The corresponding values of
plate circuit current are shown by tha
portion Of the plate current curve
OR.
During the next or third quarter
of cycle the applied grid potential
increases from zero at L to a maxj-
mum positive value at N, equal to
Oh, and causes the plate circuit to in.
crease from 1-B. liz; value when the
plate potential is zero, to I'D, an in
crease in plate current equal to I'D.
During the remaining fourth quar-
ter of a cycle as the applied grid DO
tential varies from a maximum posi-
tive value at NJ to zero at n, the plate
circuit current varies from a value s
to T.
Assuming, that the characteristic
curve as shown in Fig. VIII and Fig.
TX was with a potential of 40 volts
on. the plate, then, if the plate current
is to be reduced to zero by a yaria.
ton of plate voltage-with no poten-
tial applied to the grid-the plate
voltage must be reduced to. zero. or a.
reduction Of 40 volts must be made.
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