The Hartford herald. [volume] (Hartford, Ky.) 1875-1926, 1922-08-02

grid, determine the value OF Il. u Is
the negative potential which must be
applied to the grid in order to reduce
the plate current to zcro. The value
of T, which is the positive grid pOten-
tiai that will cause the maximum or
s;Ituratiun current to flow IN the plate
circuit, is also determined by the reia-
tive position of the grid with respect
10 the iilament and plate. II the grid
is of very fine MESH the value of T.
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charge the grid and will he repealed.
Similarly "a small positive charge ap-
piled to a 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 APP
ertures In the grid without coming in
So close to the charge on il 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
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
"a han tho grid had m nnfantial
piled to il.
A negative potential of OH rs now
applied 10 the grid where OH is Squal
in value to OIL, bat opposite in sign.
The application of the negative po-
tentlal when applied to the grid will
cause the plate current to be reduced
TO u 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 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 rectilier of
radio signals.
The incoming radio signal is "a high
frequency alternating current. Let us
apply an alternating difference of po-
teniial whose gaXlmun positive val
ne Is equal Ia Of and whose maximum
negative value is equal to OH, to the
grid of the three-elect rode tube
whose characteristic curve is the same
as that shown in Fig. VIII. In Fig.
~ is shown the alternating difference
of potential applied TO the grid
Through the first quarter of cycle.
from zero at ! to II maximum mega
tive value at X, equal To OH, the
plate circuit current will vary from
O-G, It's value AT l. when no grid pO-
tentiai Is applied to value at q equal
to He.
During the next quarter of a cycle
the grid potential changes from Il
maximum negative value nj 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 MAXI
mum positive value at NJ, equal to
OIL, and causes the plate circuit to in.
crease from l.B, its value when the
plate potential is zero, 10 I'D, an in.
crease in plate current equal TO BID.
During the remaining fourth quar-.
ter Of cycle as the applied grid po-
tentlal varies from maximum posi-
tive value at NJ 10 zero al n, the plate
circuit current varies from value \
to II.
Assuming that the characteristic
curve as shown in Fig VIII and Fig.
TX was with potential of 40 volts
ON the phte. then, II the plate current
Is 10 be reduced TO zero by varia-
ton Of plate yoltage-with no poten-
ual applied to the grid-the plate
voltage must be reduced 10 zero or a
a hs. "A