Askov American. [volume] (Askov, Pine County, Minn.) 1914-current, 1922-07-06

grid. determine the value Of f. ID ID
the negative potential which must be
applied to the grid In order to reduce
the plate current To zero. The value
OF +, which Ii the positive grid poten-
tial that will cause the maximum or
saturation current to flow In the plate
circuit. Ia also determined by the rela-
tive position Of the grid with respect
to the filament and plate. II the grid
10 Of very fine mesh, the value Of Il
IL 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charge the grid and will be repealed.
Similarly a small positive charge APP
piled to fine mesh will tend to ac-
celerate the velocity Of the electrOns.
In case Of very coarse mesh grid.
the elecfrons can pass through the ap-
ertures In the grid without coming In
% close to the charge on II and q
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 Ia Fig. VIII. O-G. Is the
current that will How In the plate cir
cult when there IL no potential ap-
Piled to the grid. Suppose a positive
potential as OIL In 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 ap-
piled to II.
negative potential Of OH ~ now
applied to the grid where OH In Squal
In value to OIL. 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 value He or A-C. less than II
was when there was no potential ap-
piled to the grid. So Il 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
IL used rs detector or rectitier Of
radio signals. s,.ssSsre 49, ~t,-,..--.
The incoming radio signal Is a high
frequency alternating current. Let us
apply an alternating difference Of pO-
tentiai 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
IN Is shown the alternating difference
OF potential applied to the grid.
Through the first quarter OF a cycle,
from zero At to a maximum mega.
tive value at X. equal to OH, the
plate circuit current will vary from
O-G. Its value at + when no grid 20
tential Is applied to value at Q equal
to H-Ca
During the next quarter Of a cycle
the grid potential changes from
maximum negative value mt X to zero
at l.. The corresponding values Of
plate circuit current are shown by the
portion of the plate current curve
OR.
"f cycle the applied grid potential
increases from zero at l. to a maxi.
mum positive value at NJ. equal to
OIL. and causes the plate circuit to in
crease from In. Its value when the
plate potential II zero. to In, an in
crease In plate current equal to BID.
During the remaining fourth quar-
ter OF cycle as the applied grid DO
tential varies from 4 maximum posi.
tive value At NJ to zero at N, the plate
circuit current varies from q value s
to +.
Assuming that the Characteristic
curve 40 shown In Fig. VIII and Fig.
IN was with potential Of 70 volts
on the plate, then. II the plate current
Is to be reduced to zero by 4 varia.
ton Of plate voltage-with no poten.
tial applied to the grid--the plate
voltage must be reduced to zero or a
reductions Of - volts must be made.
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