The Ward County independent. [volume] (Minot, Ward County, N.D.) 1902-1965, 1922-07-06

grid, determine the value Of f.. f. is
the negative potential which must be
applied to the grid in order to reduce
the plate current to zero. The value
of T. which is the positive grid poten-
tia1 that will cause the maximum or
SlturatiOn current to flow in the plate
circuit, is also determined by the rela-
tive position of the grid with respect
to the tilanrnt and plate. If the grid
is of very fine mesh, the value of +
is small because the electrOnS in pass
ing through the small mesh of the
grid on their journey from the fila
9nent 10 the plate will negatively
charge the grid and will be repealed.
Similarly Il small positive charge APP
piled TO Il fine mesh will tend to ac-
f:eler;lte the velocity Of the elertruns.
In ease of Il very coarse mesh grid,
the electrOnS cam pass through the APP
&.rt,lreS in the grid without coming in
so close to the charge on it and Il
relatively high potential will be re-
tiuired on the grid to control the cleo
ron stream, or in other words, the
current flowing in the plate circuit.
Referring to Fig. VIII, O-G. is the
':urrrnt that will flow in the plate cir
%.Hit when there is no potential APP
piled to the grid. Suppose II positive
potential as Oh is applied to the grid.
The corresponding plate circuit current
wiH be I'D or ED, more than it was
when the grid had no potential APP
piled to it.
negative potential of OH IS now
applied to the grid where OH is ru,lal
in value to OIL, but opposite in sign.
The application of the negative pO-
;te,rista when applied to the grid will
cause the plate current to be reduced
TO Il value He or A-C, less than it
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 us much as the same positive
.p0tenti;rl increased the plate circuit
current This irregular cunductivty of
che tube is made use of when the tube
is used as Il deter1Or or rectiiier of
radio signals.
The incoming radio signal is high
Frequency alternating current. Let us
apply an alternating difference of pO-
tensi:li whose maximum positive val
ne is equal to OF and whose maximum
neg3tive value is equal to OH. to the
grid Of the thrce-elrctrode tube
whose characteristic curve is the same
as thai shown in Fig. VIII. In Fig.
IN is shown the alternating difference
of potential applied t" the grid
Through The first quarter of ii cycle
from zer" IT J to Il maximum mega
live ralne 1T X. equal to OH, the
plate circuit current will vary from
'o+;, lis value ut Z when no grid po-
genital is applied to Il value at @ equal
SO He
During the next Quarter of d cycle
che grid potential changes from a
znaxinlm negative value at X to zero
at l. The corresponding values of
plate scircuit current Are shown by the
portion Of the plate current curve
OR,
During the next or third quarter
1f a cycle the applied grid potential
Increases from zero at l. to a maxi
mum positive value at NJ, equal to
1eI, and causes the plate circuit to in
crease from lib. it's value when the
plate potential is zero, ITO I'D, an in
screase in plate current equal to BID.
During the remaining fourth quar-
tier Of a cycle as the applied grid po-
.tential varies from a maximum posi-
tive value at NJ to zero at n, the plate
circuit current varies from value S
to r. ...s.. a
Assuming that the characteristic
curve as shown in Fig. VIII and Fig.
Il was with a potential Of 40 volts
asn the plate, then, if the plate current
rs to be reduced to zero by varia-
ton Of plate vOltage-with no poten-
fiaI applied to the grid-the plate
voltage must be reduced to zero or a
reduction of 40 volts must be made.