Re: Ignitrons for sale

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jimlux-at-earthlink-dot-net>

 >
 > >        Can I ask, what is an ignatron?
 >          An ignitron.
 >
 >          A web search on this spelling will be most productive.
 >          Roughly:
 >          a mercury vapor filled 'vacuum' tube, with many of
 >          the characteristics of an SCR.  Proceded SCRs by decades.
 >
 >          There is a family of 'controlled rectifiers' called
 >          variously ignitrons, thyratrons, etc, with similar
 >          characteristics.  Some portion of the difference seems
 >          to be as much PR, Patent Lawyers, etc, as technology.

Although this may seem to be the case, there are big differences between a
mercury vapor thyratron and an ignitron.  Functionally, you have it right,
they are both devices  that a) are basically a  DC device and b) are
triggered on and then stay on until current drops.

Ignitrons have a pool of mercury in the bottom forming  the cathode.  A
biggish pulse to an electrode (often made of rough surfaced carborundum)
that pokes into the surface of the pool vaporizes some of the mercury,
allowing current to between cathode and anode, which heats up more of the
mercury, etc.  These puppies can be made to carry very large currents
(kiloamps) for extended periods of time (milliseconds).  Ignitrons are used
in low frequency applications (i.e. phase control "dimmers" for 60Hz, welder
controls, etc.)

A thyratron is a bit different.  It has a gas in it (mercury vapor,
hydrogen, and deuterium are popular), the pulse between grid and cathode
ionizes some of the gas, triggering it on.  These two can carry very large
currents, but the average power handling (for the same physical size! don't
start sending me emails about those giant Fxxxx thyratrons at SLAC) is
lower.  Thyratrons turn on a lot faster (way sub microsecond) and turn off a
lot faster (same) than ignitrons.