New-York tribune., 1922-10-15
Radio Receiver Connection
Most perplexing TO Fans
Outlined and Its Basic
Principles Are Described
Three Circuits ON Tube
Need Negative Potential
OR Radio Arnplificasion;
Battery Plus 10 Detector

Where several parts of the circuit are
joined together.
The puzaling feature of this connec-
ton is that almost every diagram pub
ilshed shows it different, the result
being that the radio novice who de.
sires to construct his own set is left
in bewildering maze of doubt as to
just which is correct and which is
wrong.
1t is my purpose therefore in this
story to outline the basic principles
which determine the correct method
or joining vacuum tube circuits to-
gcther.
o Thrcc Different Circuits
In the first place it should be dis
tlnctly borne in mind that there are
three different circuits in a vacuum
tube set, no matter where or for what
purpose the tube is being used. These
are first the iilament circuit, which of
course heats up the filament and causes
1t TO emit negative electrons from it's
surface. Second, the grid circuit.
which acts as the control element of
the tube, and third, the plate circuit.
Inc fllanrent circuit is from the posi-
tive OF the storage battery through one
side of the filament, out of the other
side of the filament, back to the mega
tive post of the storage battery The
gr.d circuit consists of the tuner Cor
in the case of amplifying circuits, the
secondary of the transformer to the
grid, and the other side Of the tuner
OF tran5T ormer to one side of he fila
ment The plate circuit runs from the
plate through the telephones (or
primary of transformer through the
high voltage, or B battery to the fla
ment In both the case of the grid
and the plate circuits. their individual
circuits are completed inside the
vacuum tube from the filament.
Now let us take first of all the
vacuum tube used as an amplifier for
radio frequencies. That is in cases
where i. Is used to amplify the weak
radio impulses picked up by an aerial
before those impulses are passed
through the detector for rectification
There are number of tricky things
connected with this form of amplifi-
cation, and it is necessary that the
circuit used in connection with it be
kept in the utmos. state Of stability
that it is possible to obtain, otherwise
nothing but squeals and bowling will
result.
Negative Potential Needed
1t is necessary therefore that
negative potential be maintained on
the grid of ali the radio frequency
simplifying tubes. In the first stage
of radio frequency this can be ac-
complished BY means Of a potentio-
meter placed across the storage bat
terry. and thc center contact of the
potentiometer being connected to the
tuning element in the aerial circuit
The path is then from the filament
through the tuner to the grid. By
means of the potentiometer the cor
rec. amount of negative potential can
be regulated and placed on the grid.
Since a negative potential is i'm
lorative for this purpose the negative
side Of the storage battery will be the
common lead" for all radio frequency
simplifying tubes. In other words, one
frequency transformer will be con-
nccted to the grid and the other side
of this transformer will be joined to
the negative side of the storage bat
terry in every case
When we come to the use of the
vacuum tube as detector we are
confronted with an entirely different
situation. In this case there will be
a constant ccuniulation of negative
olectrons on the grid of the tube dur
ing it's operation, and unless there is
some means provided this charge will
interfere with the proper functioning
Of the tube.
Grid Leak Required
The method universally adopted to
take care of this situation is by means
of a grid leak. This is nothing more
than a very high resistance, which
normally is in the neighborhood of
one megohm-or, expressed differently
--one million ohms.
Now in order that the negative
charge can leak off from the grid and
permit the tube to operate efficiently as
a detector it is necessary to join the
other side of this grid leak to the posi-
tive side of the storage battery. This
is based on the fundamental law that
sequently the positive side Of the bat
terry draws off the negative charge
through the leak, while the grid con-
denser permits the high frequency cur
rents TO pass through to the grid of
the tube without interfering with the
action of the grid leak
In the case of the vacuum tube be-
ing used for the purpose of audio-fre-
quency ampliication, the common lead
will also be to the positive side Of the
storage battery. This is because of the
fact that the audio-section of the re-
ceiver is joined directly to the de-
tector tube.
Such are the basic principles which
govern the common lead Of the vacuum
tube in the different uses to which it
may be put. There is very important
point that could be we'll included in
this article in connection with radio
frequency amplifcarfon. When this
form of amplification is used on short
waves very serious difficulties are en-
countered because of the high FREE
quencies involved. 1t is imperative
under the circumstances that capacity
in the circuit be kept down to a mini
mum.
Where more than one stage Of radio
frequency amplificatlon is used it is
very unwise plan to use Jacks be-
tweeen the stages. Some fans do this
for the purpose of facilitating opera
tlon IN bringing in one or more stages
OF amplification, just the same as thew
do with audiofrequency amplification.
Inc Jack, however, acts as a condenser
IN the radio section of the receiver.
and should not be used. In fact. the
wire connections between the varions
parts in the radio amplification sect;on
Of the set should be kept as short : : q
is physically possible in order to oh =
tain the best results.
Government Has Ten Stations
The Federal government now main
tains ten broadcasting stations for the
purpose OF sending out crop and mar
ket news. -~ 80