Essex County herald. [volume] (Guildhall, Vt.) 1873-1964, 1922-06-29

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
of f, which is the positive grid poten-
tial that will cause the maximum or
saturation 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 K
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charge the grid and will be repealed.
Similarly small positive charge APP
piled to fine mesh will tend to ac-
celerate the velocity Of the electrons.
In case of a very coarse mesh grid,
the e1ectrons can pass through the APP
ertures in the grid without coming in
so close to the charge on it and
relatively high potential will be re-
quired on the grid to control the cleo
iron 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 APP
pied to the grid. Suppose positive
potentiai as OIL 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 APP
piled to it.
A negative potential of OH rs now
applied to the grid where OH is Squal
in value to Oh, but opposite in sign
Che application of the negative po-
tential when applied to the grid will
cause the plate current to be reduced
to value He or A-C less than it
was when there was no potential ap-
piled to the grid. SO it 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 a detector or rectifier Of
radio signals.
The incoming radio signal is high
frequency alternating current. Let us
apply an alternating difference of po-
tential whose maximum positive val
Ge is equal to Oh ard 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 a cycle,
from zero at j to maximum mega
tive value at K, equal to OH, the
plate circuit current will vary from
O-G, its value at Z when no grid pO-
tential is applied to value at Q equal
10 H-CA
During the next quarter of q cycle
the grid potential changes from 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 a cycle the applied grid potential
increases from zero at l. to a maxi
mum positive value at M, equal to
Oh, 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 cycle as the applied grid pc.
sential varies from a maximum posi-.
tive value at NJ to zero at N, the plate
circuit current varies from a value
to Il.
Assuming that the characteristic
curve as shown in Fig, VIII and Fig
TX was with potential of 40 volts
on the plate, then, If the plate current
is to be reduced to zero by varia
ton of plate voltage-with no poten
tial applied TO the grld-the plate
voltage must be reduced to zero or q
J reduction of 40 volts must be made