deForest did it, so can we.

Robert E.Seastrom rs at
Mon Jun 19 18:59:00 CDT 2006

hal <hfeinstein at> writes:

> (2) Next skill, what do you
> make the filament out of?  I think you can buy thoriated
> tungsten, yes, but  I wonder what old DeForest used for
> his filaments?  Nickel wire? 

wikipedia article:
has a link to the patents.  841,386 says in part:

   While various means may be employed for heating said gaseous medium I
   find it convenient to employ electrical means and, therefore, I prefer
   to employ as the electrode F a filament of carbon or metal and to
   connect the same in series with a battery B' and a rheostat R'.  I
   have ascertained that a filament of metal, especially one of tantalum,
   renders the oscillation-detector much more sensitive than one of

it is not surprising that deforest would try tantalum as it was an
interim filament material in light bulbs after carbon lost popularity
and before tungsten was adopted (tantalum is pretty friendly to work
with whereas tungsten is not very ductile - not sure what was done to
be able to work it into light bulb filaments, but i suspect that it
probably involved super high purity and very carefully controlled
alloying).  according to sylvania's web site, the thoriated tungsten
wire is preferred for arc lamps and power tubes.

but i digress.  tantalum wire is not particularly expensive stuff,
considering the quantities of it we're anticipating using.:


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