deForest did it, so can we.

hal hfeinstein at
Mon Jun 19 21:31:56 CDT 2006

This URL is a picture of a home made audion. Its made from a bell jar. 
An ashtray is used
for the base. Rob, where do you order tantalum wire from? And is the stuff
dangerous to heat up and work with?

Robert E.Seastrom wrote:
> 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
>    carbon.
> 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.:
>                                         ---rob

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