January 1933 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
If this article had appeared in the New York Times in the
year 2014, its author, Glenn Ellsworth, would have been labeled
a 'Depression Denier!' Don't be confused by the word 'denier,'
which most often prior to about 1999 was used to refer to a type
of silver coin or a measure of fineness of silk cloth. Today, it
is seen most often as describing one who would deny something. 'Denyer'
is the alternate spelling used by some authors to avoid confusion,
and since the level of spelling knowledge is so low, most people
never notice. But, I digress. The reason I bring up the point is
because this article was published in 1933, little more than three
years after the Stock Market Crash of October 29, 1929
Tuesday'). Mr. Ellsworth says in part, "Many service
departments are fairly busy, even with the so-called
depression at its height." His audacity would nowadays
earn him pariah status and negate any value his work might otherwise
bring to the science world. As long as I'm pointing out contemporary
expectations, I'll also mention that a modern magazine would show
the person holding the tube as wearing a full suit of battle gear
including non-asbestos, heat-resistant welding-type gloves, a UV-impregnable
welding helmet, ear plugs, and an emergency reaction medical and
firefighting team standing by with lights flashing on all vehicles.
Isn't is amazing that our ancestors survived long enough to make
your and my presence possible?
Blowtorching Tubes to Life
the April, 1930, issue of Radio-Craft appeared an interesting article
by George Stoneham regarding a baking process in bringing back to
a semblance of activity those tubes which have tungsten filaments.
Mr. Stoneham used a reflector set over an electric heater in
his experiments. In all probability the results obtained are the
same as those secured by the author; however, there are a few drawbacks
to the method described by Mr. Stoneham.
Many service departments are fairly busy, even with the so-called
depression at its height and, what with trying to do several men's
work, the shop technician is inclined to forget that he has one
or more tubes in the cooker. The continued heat of the electric
stove will melt the cement which holds the glass to the base and
while the cement no doubt will harden again as the tube cools, the
cement crystallizes, with the result that a slight strain will break
it. Another drawback of the baking process is that the tube cannot
be watched during the operation.
A description of the procedure and results of experiments in
our shop, with all the later tube models, both heater and filament
types, may be of interest to other radio men.
After having recorded the tube characteristics, subject the tube
to the slow heat of a blowtorch, as shown in Fig. 1. (The torch
illustrated is a Ratco part No. 4061; the 4 in. flame will reach
a heat of over 2,000 deg. F.) Hold the tube two or three inches
from the point of the flame and revolve the tube slowly.
Bring the "patient" closer and closer to the flame, until the
flame comes in contact with the glass, and keep the tube in this
position until the silvery deposit on the interior of the glass
envelope has been driven off.
The operator will notice that within a second or two from the
time of contact with the flame a round spot which is clear of the
deposit will appear inside the tube; the best results will be secured
by following the deposit with the flame and driving it from the
glass of the tube itself. Finally, place the tube in a location
where it may be permitted to cool slowly and without chilling.
The cooling process finished, place the tube in the tester and
compare the present readings with those taken before the operation;
then put them in a set and compare the performance with that of
a "known" new tube. The results will be very gratifying; in fact,
this procedure may even be tried on a new tube that does not quite
come up to standards of an individual service department, with surprising
This reactivation process has been applied to the following tube
types: the '24, '30, '31, '27, '26, '71, '45, '47 and '51. In fact,
we are using in a short-wave receiver a set of '30's, '31's and
a '32 which had been thrown into the junk box as of no further use
but which, when reactivated by the blowtorch method, came to life
in great shape and are still' doing service comparable with that
of new tubes, after seven months of continued use.
Our best results were obtained from tubes that showed a heavy
deposit on the inside of the glass, while tubes having very little
of the deposit generally did not react to the treatment. The proportion
of cures to incurables is about 80%; about 20% were quite beyond
recall from the limbo of defunct "valves."
It has been brought to the attention of the writer that one experimenter
has found that the glass may melt when using the baking process;
probably the tubes were exposed to a temperature greater than 3,700
deg. F. In using the torch, the tube is constantly under the eye
of the attendant and as soon as the deposit leaves the surface of
the glass, the flame is directed to another portion of the envelope.
This same technician has reported that tube noise had increased
after reactivation. The chances are that noise would have been experienced
anyway, due to looseness of the elements which will be found at
times even in some of the best known brands, however, we have not
found any trouble in this respect.
In our service work we have picked up a goodly number of extra
dollars by availing ourselves of this "kink." A nominal fee of 35c
per tube is charged and the customer figures that we are pretty
good Service Men to do business with, since we have not stuck him
for the price of new tubes; also, he figures that we must know "our
stuff" to be able to offer him this unusual service, and he passes
the good word along to his friends. Of course, it is not advisable
to discourage potential sales of new tubes, but this stunt is a
mighty handy "ace" for use in many instances where time, money or
some other factor is of importance.
Posted January 16, 2015