1966 Mag: Build NE-2 Neon Bulb Computer - scan available

[Brent Hilpert]

William Donzelli wrote:
> 
> > > Ignitrons are very different beasts from thyratrons.
> >
> > They're both gas-filled power-control devices performing similar functions.
> 
> Mmmm...sort of. After a few beers.
> 
> Thyratrons can contain gases or mercury (or I think, in some case,
> both), and they still use a filament, much like a normal tube
> (pliotron or kenotron, if any GE people are keeping score) and some
> sort of grid for control, although in many thyratrons the grid looks
> nothing like a grid. Thyratrons are used for control rather than
> rectification, although one can rectify with them (IBMs power supply
> for the 709 - they were likely used to give some sort of help in
> regulating the DC output).
> 
> Ignitrons use mercury (I have never heard of one that does not,
> although krytrons are pretty similar) and do not have filaments. The
> conductor is the mercury plasma created by the igniter arc, and
> conduction is more or less the arc between the pool and the anode.
> Ignitrons tend to be used more for rectification than control(and when
> used for control, they tend to be simple on-off, rather than the more
> sophisticated setups thyratrons are often see with).

Not 'sort of', and one doesn't need beer to see their similarities. They are
sub-classes of a common class; yes, there are differences, otherwise they
wouldn't have different classification names, but the fundamental principle of
using ionized gas to reduce conduction losses is the same. They are both
triggerred on-off devices and ignitrons were used very much in
controlled-rectification applications, their switching speed is actually
reasonably fast ("usually less than 50uS"), making them fine for control in
60Hz systems, as with thyratrons. They are typically discussed in the same
section in textbooks.  They perform similar or nearly identical *functions* -
their final *application* may typically differ due to different specs (notably
higher current capacity for ignitrons), although I would suggest there are
areas where their final application could cross over.

To quote from a reference at hand: "The great advantage of the high-current
and overload capacity of the mercury pool has been combined with the control
versatility of the thyratron in the ignitron."