Evening star., 1923-06-24

for fully 20 per cent of the sickness
from which receivers suffer, and al
most automatically now in diagnos-
ing the case of a Sinck one one looks to
the leak Unless il is constructed
right and then used right the receiver
it is used in will never function prop
erry.
In order to understand thoroughly
the Importance of this unit it is nee
essary that a full knowledge of it's
every radio fan. 1t is, therefore. the
purpose of this article to briefly out
line the operation of the leak.
After all. this operation is really
without any technicalities whatso
ever. It is bound up in the valve
like section of the vacuum tube when
that remarkable instrument is being
used as a detector in the receiver
BY this time even the newly initiated
makes it possible to reproduce the
sounds which are put into the micro
phone at the transmitting station.
Now, the manner in which the
The electro magnetic waves. which
travel through the ether and are
picked up by the receiving aerial set
up fgh-frequency current In the
tuning elements of the receiver it.
self. The tuning element. of course,
ing wave. This in turn applied
across the grid and f1lament of the
vacuum tube.
1t is then that the tube. as de-
When the filament is lighted by cur
rent from the storage battery it emits
electrons. These little particles are
negative electricity. Since the plate
Of the vacuum tube has a high volt
age battery connected to 1t in such
t.l t.,
tanned on the plate, the electrons will
be attracted there, because unlikes
attract each other.
When the current impressed on the
grid Is positive the grid will aid in
this passage from the filament to the
plate. When. however, the grid Is
negative 1t will resist their passage,
because like and like repel each other
and since the electrons are negative
and the grid Is negative there will
be no further flow.
In this manner the vacuum tube
acts as valve, allowing only one
half of the alternating current to
pass through 1t and completely check
ing the other half. The result is that
there is a flow Of pulsating current
one direction only, and it is this
which actuates the telephones and
reproduces audible signals.
During the normal operation Of the
tube as a detector it will happen that
an excessive negative charge will be-
the electronic stream from the fla
ment. This charge tries to go some-
where when It reaches the full ca
pacity of the grid element. 1t will
leak off through the socket Of the
tube. or even the walls of the tube
along the path of least resistance.
This action, however, its too slow
and permits the grid to accumulate
full negative charge before leakage
begins.
It is necessary in order to keep the
tube from blocking up to provide a
pathway for this excessive charge to
leak off without in any way inter-
fering with the other normal function
of the tube or the circuit associated
with it. That Is the exact job Of the
grid leak.
Now. If this leak is to function
properly 1t must not be too high
resistance nor too low. Moreover, 1t
must be SO placed that 1t will form
to leak off. It is here that the most
important point to remember should
be stated. In the detector the return
OF the grid circuit must be the posi-
tive side of the filament circuit. The
word must" in this case cannot be
overemphasized.
The reason is very simple and 1t Is
bound up in the elementary principle
that unlikes attract and likes gepel
each other. Since, therefore, it is
negative charge which we wish to
get rid of we must have a positite po-
tential at the other side of the circuit
in order to attract the negative
charge-hence the reason for COM
pleting the grid circuit at the positive
side of the filament.
The grid leak functions perfectly
normally without interfering with
the high frequency currents, which
are impressed on the grid when sig
nal is received. The latter find an
easy pathway through the grid con-
denscr because OF their high fire.