Pullman herald. [volume] (Pullman, W.T. [Wash.]) 1888-1989, 1922-06-30

2Eld, determine the value of f. T. is
ti-H negative potential which must be
applied to the grid in order to reduce
lhe piate current to zero. The value
OF r, which is the positive grid noten-
tlal that will cause the maximum or
saturation current to flow in the plate
circuit Is also determined by the rpla-
tive position of the grid with respect
70 The hlament and plate. If the grid
IS vi very line mesh, The value OF l.
is small because the eleCtrOns in paSS-
ing through the small mesh of the
grid on their journey from the fla
nent 10 the plate will negatively
charge the grid and will be repealed.
Similarly small positive charge an
pied to fine mesh will tend to ac-
CELEBRATE the velocity of the electrons.
In case of a very coarse mesh grid.
The electronS can pass through the an
ertureS in the grid without coming in
50 close to the charge on il and a
relatively high potential will be re
CURED on the grid to control the elpc-
tron stream, or in other words, the
current flowing in the plate circuit.
Referring to Fig VII. 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 it was
when the grid had no potential aIe
piled TO it,
A negative potential of OH RS now
applied TO the grid where OH is Nqual
in value to Oh, but opposite in sign.
The application of the negative DO
tential when applied to the grid Will
cause the plate current to be reduced
TO value He or A-C, less than /.
was when there was no potential APP
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 rectifer 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 OIL 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 a cycle.
from zero at J to "A maximum mega
tive value at X, equal TO OH, the
plate circuit current will vary from
O-G, its value at 7 when no grid po-
tential is applied to a value at Q equal
to He
During the next quarter Of cycle
the grid potential changes from
maximum negative value at X 10 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 NJ, equal 10
OIL, 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 po-
tential varies from maximum posi-
tive value al NJ 10 zero at y, the plate
circuit current varies from a value :
to T.
Assuming that the characteristic
curve as shown in Fig. VIII and Fig.
IN was with 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 10 zero or n
reduction of 40 volts must bp made