Evening star., 1924-05-20
new RADIO TUBES
MARK BIG ADVANCE
Burnt-Out Filament Is No Longer
Cause of Trouble and
Expense.
STRONGEST EVER BUILT
New Invention Solves Problem of
Repairs.


Copyright, 1924, by North American News
paper Ailiance.)
~ new kind of vacuum tube for
use in radio broadcasting stations
mas been perfected in France and is
now in use in the great sending
station at the Eiffel Tower, in Paris.
Not only Is the new tube one of the
most powerful ever built, but it in
wolves principles of design and oper-
atlon SO novel as to constitute a real
~ revolutionary advance in this part
Of radio technique.
The new tube will come apart
any time for repairs and readjust-
ment. 1t does not have to be pump
ed out in advance by a vacuum ma
chine; on the contrary. the pump
.nat maintains the necessary vacuum
is continually attached to the tube
itself The tube is kept pumped
Gown continually to any desired de-
calls hardness"
The new design was invented by
Prof. F. Holweck. a well known
physicist of the Institute de Radium
ana an International expert on the
proouctlon and use Of X-rays. In
oeed. 1T was for the generation of
tne hlgh-voltAge currents used in
1ray work. not for radio use. that
new type OF tube. But tests of the
new tuoes in the Eiffel Tower sta
tlon showed them so useful for radio
thahsmission th that this. rather than
the use in N-ray machines. promises
70 be their main utility to science.
Cooling Is Easy.
The first tubes built on the new
design had a rated power of 10 kilo-
watts. More recently a l5-kilowatt
tube has been built and still larger
ones are proposed. The demountable
construction of the tube not only
permits easy repairs, but facilitates
the design of the artificial cooling
devices that become so necessary with
tubes handling an amount of power
Is great as this.
The flament of the tube is not yery
dlherent from the usual designs, but
the plate. instead of taking any Gus
tomary form. is copper cylinder
that entirely surrounds the filament.
Outside this copper cylinder there is
space in which water circulates in
order to keep the plate cool. The
grid, interposed. as usual. between
the filament and the copper cylinder
that replaces the plate. is of heavy
molybdenum wire.
The copper cylinder that acts as
plate is clamped at either end to
short glass tubes of about the same
diameter. One of these tubes carries
the sealed-in connections for the cleo
trio circuits to the filament and grid.
The other glass tube serves merely
as connection to the pump that
maintains the vacuum.
Can Keep Vacuum.
The connections between the copper
cylinder and the two glass tubes, as
well as all other necessary connec-
70 hI nd ynin
sealed by rubber gaskets. All are
clamped down tight and the rubber
used is of a special quality that will
not give OF gases. With all joints
properly closed and clamped the tube
can be maintained at as perfect a
vacuum as any other kind of tube.
Nevertheless, the joints can be loos-
ened easily and repairs to internal
parts can be made without delay or
damgae to other parts of the appara-
tuS
In operation the pump and the
tube are kept in continual connection. |
Tho glass tube sealed onto the lower |
end of the copper cylinder mentioned |
this joint, too, being carefully ground |
SO that it is absolutely tight. The |
pump itself operates, in the usual
fashion, by means OF a metal cylinder
rotating very rapidly inside a cylin-
drical case. The rotation Of the cylin- |
der drags the particles of air along
and removes them from the part of
the cylindrical case to which the
vacuum tube is connected. DIR. Hol-
week has perfected, also, a detailed
design of this pump. involving espe-
ctally series of grooves on the re-
volving cylinder and on the inner side
of the case in which it revolves. The
resulting pump is said to be much
more perfect and efficient than any
pump of this design previously built |
In operation the vacuum tube is
carefully put together. all joints are
closed, the tube is attached to the
pump and the pump is started. In a |
short time the vacuum is sufficiently !
perfect. the current is turned on and |
broadcasting can began. AS long as |
the tube Is in use the pump is kept in |
rotation and the vacuum is thereby |
maintained.
Saves Tube Breakaxe.
tubes has been used for broadcasting
except at the Eiffel Tower station
1t is probable, however. that other |
broadcasting stations will obtain and |
try them before long. and their ad- |
vent in the United States will prob |
ably not be long delayed. AS broad
casting stations become more and
more powerful the tubes of ordinary
design becomes more and more costly. |
Tube breakage becomes a serious ex-
pense.
And with the present design Of
tubes used in the United States any
breakage inside the tube. as, for ex-
ample. burnt out filament, is like
1y to mean that the tube is ruined al
together. 1t is impossible to take
these tubes apart without opening
the glass bulb and resealing 1t later !
With the Holweck tube this matter |
or repairs becomes a very simple and |