The Ely miner. [volume] (Ely, Minn.) 1895-1986, 1926-01-01
BY ARTHUR r. MoRAsH, S. g.,
In Boston Herald


Many radio fans have, no doubt,
which inactive tubes may be restored
to their former activity, but according
to the many questions concerning 1t,
there has been evidently shroud of
mystery cast over the process.
Some know from observation, and
many others know through sad eX-
perience, that the vacuum tube con-
tains a filament that becomes lumi-
nous when current passes through
1t. This filament receives its cur
rent from the A battery. Contrary
to the popular belief, the filament is
not put in the tube for illumination
purposes, but to serve as a source of
the electrons necessary In the mech
anism" of the vacuum tube. A more
technical term for the filament Is
''hot Cathode" and simply means that
1t becomes a source of negatively
charged particles known as electrons
when 1t reaches the proper tempera-
ture. This temperature is obtained
by passing current through the fila
ment. For this reason 1t would per-
haps be more to the point to call
this current the heating instead of
the more common expression, "fila-
ment" current.
Treating Fiiaments.
The first filaments were of pure
tungsten, carbon, platinum, ETC., but
1t was soon discovered that the num-
Der of electrons emitted by the hot
cathode, or filament, could be enor-
mously increased by coating the sur
face of the filament with certain
chemical compounds. The compounds
that proved to be the most active in
this respect are the alkaline earth
oxides, such as barium, calcium, stron-
tium, etc.
However, a still more active mate
rial was discovered in recent years,
and is known as "thorium oxide" 1t
may be of interest to know that it Is
of the titanium series of chemical
elements, and is used in the forma-
ton of incandescent gas nantes.
Another very interesting fact is that
1t is radioactive.
general types of filaments have come
into prominence, they being the oxide
coated filaments and the thoriated fl
ament. The WD11 and II are ex-
amples of the former, while the UV199
and UV201A tubes are in the latter
class. AS the oxide-coated filament
cannot be rejuvenated, I will not dis
urfhn in, "a, ;ola h,,+
will focus my entire attention on the
thoriated style element.
This type of filament consists Of
tungsten core that has been treated
with thorium oxide, not merely coat
ed with the compound, but actually
impregnated, so that the amount of
active material on the surface Of the
filament is comparatively small In
comparison with the total amount. 1t
is because of this feature that tube
employing a filament of this variety
seldom goes out of service because of
a burned-out filament, but because the
emission has dropped below the
necessary value. When this condition
has been reached the tube is said to
De ludctlVe. Lie rear significance OF
this expression is that most of the
active material has been evaporated
from the surface Of the filament, and
as a consequence the number Of cleo
irons emitted is reduced to very low
value.
How to "FIash" a Tube.
This process merely consists of
burning the filament by passing
current through 1t, but with the B
battery totally disconnected. Why
should the B battery be disconnect-
ed during the reactivating measures?
Well, this is necessary because with
the B battery connected, the posi-
tive high voltage charge on the plate
would cause the material to become