deForest did it, so can we.

[hal]

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?

http://www.sas.org/tcs/weeklyIssues/2004-05-28/review/art/triode2b.jpg




Robert E.Seastrom wrote:
> hal <hfeinstein at cox.net> 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:  http://en.wikipedia.org/wiki/Audion_tube
> 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.
> http://www.sylvania.com/BusinessProducts/MaterialsandComponents/ElectronicsDisplayProducts/TungstenWire/
>
> but i digress.  tantalum wire is not particularly expensive stuff,
> considering the quantities of it we're anticipating using.:
>
> http://www.sisweb.com/ms/sis/wire4.htm
>
>                                         ---rob
>
>
>