The Beaver herald. [volume] (Beaver, O.T. [Okla.]) 1895-1923, 1922-07-20

grid. determine the value Of II. Il Is
the negative potential which must be
applied to the grid In order to reduce
the plate current to zero. The value
of +, which is the positive grid poten-
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 flament and plate. II the grid
Is of very fine mesh, the value of Il
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 win tend to ac-
celerate the velocity OF the electrons,
In case of a very coarse mesh grid,
the electrons can pass through the ap-
ertures In the grid without coming In
so close to the charge on II and
relatively high potential will be re-
quired 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 positive
potential as OIL is applied to the grid.
The corresponding plate circuit current
will be I'D or BID, more than II was
when the grid had no potential APP
piled to II.
A negative potential of OH n ,0w
applied TO the grid where OH Is oqual
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 1t
was wheE there was no potential np-
piled 10 the grid. SO II 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 conductiyity off
the tube Is made use Of when the tube
is used as detectOr or rectlher OF
radio signals.
The Incoming radio signal is "A high
frequency alternating current, Let us
apply an alternating difference of po.
tentlal whose maximum positive val
ue is equal TO OIL and whose maximum
negative value is equal to OH, I, the
grid of the three-electrode cube
whose Characteristic curve Is the same
as that shown In Fig, VIII. In Fig.
IX 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, its value at T. when no grid po-
tentlal is applied to value ut Q equal
to H-C4
During the next quarter Of cycle
the grid potential changes frcm a
maximum negative value at X to zero
at l.. The corresponding values OF
plate circuit current are shown by the
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 maxi
mum positive value at Nj, equal "a
OF, and causes the plate circuit to in
crease from I-B, its value when the
plate potential is zero to I'D, an In
crease in plate current equal to BID
During the remaining fourth quar-
ter Of a cycle as the applied grid po
tentlal varies from maximum posi-
tive value at NJ 10 zero at N, the plat,
circuit current varies from value
to T..
Assuming that the characteristic
curve as shown in Fig VIII and Fig
TX was with a potential of 40 volt
on the plate, then, II the plate curren
is to he reduced to zero by a varia
tlon of plate yoltage-with no poten
tlal applied to the grid-the plat
voltage must be reduced TO zero or
reductlop of 40 volts mus be made