deForest did it, so can we.

hal hfeinstein at
Mon Jun 19 17:58:58 CDT 2006

After looking at one web site I got thinking it might
be possible to build a basement version of a
vacuum tube triode like deForest's audion.

The basics are: Fleming put a heated electrode and a plate element into a
glass vacuum bulb to create, --the Fleming valve.  DeForest based his
invention closely (some say too closely) on Flemings work creating
a triode he called the Audion.  Some commentators say that it took
a ham named Armstrong to figure out how the Audion really worked.
Once Armstrong knew how to work with the Audion (Armstrong
devised a method of displaying relationships between grid current
and plate voltage, creating what we now call the "tube chart." He
devised one for the Audion, perhaps the first).  From this tube chart he
could now design audio and RF amplifiers. Adding RF feedback to
an Audion amplifiers he created the regenerative detector
and later, demonstrated the principle of superregeneration.

So,  how do you build a Audion that is a basic triode in your basement?
Like most projects you will need to master several auxiliary skills
to do it.  Here are the first few  (1) How to make an vacuum bulb
to hold the elements.  Remember we are working on ham budgets here,
not those of NASA.  I talked this over with Sandy.  My first
ideas was to use mercury to create a vacuum.  But, maybe you
need so much mercury that you first need a hazmat permit to
obtain it.   No luck there. A vacuum pump?  Maybe, or
successive cooling with dry ice?  (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? (3) how do you put wires to power the
filament, grid and plate through the glass bulb and still hold
a high vacuum?  And on that track:  what is "getter" and
where do you get it from? 

According to Sandy the finish line for this attempt should be to
use the homemade Audion to build a regenerative receiver
without either destroying the basement lab or fatally irradiating
ourselves.  Personally, I think chemical laboratory glassware
might have stuff we could adapt rather then creating our own
vacuum bulb.   Any ideas?


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