[ARC5] VR Tubes

[J. Forster]

More-

Once a gas discharge is ionized, and then turned off, the ionized atoms, a
few of them at least, stay ionized for quite a long time. This is true in
VR tubes and neon and fluourescent tubes. The ion lifetime is inversely
propostional to the gas pressure in the tube.,

There is a technique, called opto-galvanic spectroscopy, where light of
very precisely selected wavelengths can affect the current through a gas
discharge.

Another example is a long-used neon light, as in a Waber power strip.
After many years (5 or so) te neon pilots start to flicker. If such a
strip is in a darkened room, the pilot light often will not glow, but does
start to glow if the room lights are turned on. I've seen this on several
occasions.

In a DC voltage regulator application, the issue only arises during
turn-on. Once the supply is operating nominally, the current through the
VR tube is approximately constant, so the ionization never goes away. In a
TR tube this is not the case, of course. That's why the have a radioactive
source and/or a "keep alive" electrode...  to maintain a bit of ionization
so the thing blows over quickly and reliably on each main bang.

-John

=========




> On 8 Nov 2012 at 18:37, Robert  Eleazer wrote:
>
>> "For one thing, VR-tubes must be able to have some input from light to
>> "encourage" the formation of the internal "plasma""
>>
>> Then how does the one in my RT-7/APN-1 work given that it is sealed
>> inside a case that has only a few air holes in the back?
>
> As I said, it doesn't take much: even the ambient light that gets through
> those louvres would do the trick.
>
> As I understand it, all it takes is one or two photons to do it.
>
> Ken W7EKB
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