[Milsurplus] "Blue Glow" mystery.

[Richard Brunner]

Yes, also the anode should be dense for productive generation of x-rays, 
also cobalt, iron or copper.  I doubt a thin glass tube envelope would cut 
it.  Also 500 volts isn't much.  Also are the electrons actually accelerated 
or merely milling around?  (so many questions...I quit)

Richard


> The x-rays are generated when the kinetic energy of a fast-moving electron
> is suddenly stopped. Some comes off as radiation, some as heat. The reason
> Tungsten is used is it's high melting point.
>
> -John
>
> =================
>
>
>
>> If the blue glow is within the tube, that's gas.  If the blue glow is on
>> the
>> surface inside the glass envelope that's electrons hitting the glass, and
>> indicates a good vacuum.  When a tube is "cut-off" that does not mean
>> there
>> is absolutely NO electron flow.  As the tube approaches cut-off, it
>> approaches it as a limit, and the current is reduced to a very small
>> amount,
>> maybe a few mils or microamperes.  Electrons may also find unintended
>> paths
>> around tube parts uncontrolled by the grid, etc.
>>
>> As an extreme example, early radar modulators used big triodes, passing
>> amperes for a few microseconds with a tube voltage drop of maybe 1500
>> volts.
>> and a few milliamperes when cut off at 15 kv.  The result was the tubes
>> dissipated almost as much power when cut-off as when conducting.
>>
>> X-Rays need much more voltage drop, 10 kv comes to mind for soft X-Rays.
>> (of
>> course I'm an expert.....) You also need the right kind of target/anode.
>>
>> Richard, AA1P
>>
>>
>>>>    The dark blue glow that seems to be right at the glass
>>>> is caused by x-rays from the tube.  Its commonly seen in
>>>> tubes like audio output tubes with fairly high voltage on
>>>> the plates. Some older tubes had a black coating on the
>>>> inside of the glass to stop it.
>>>
>>> That's my big question and point.
>>> You are of course correct about the blue glow,
>>> but why is this one happening in a cut-off tube
>>> with no current flow, then disappearing when
>>> current is flowing?  That's opposite of what
>>> I've seen before.
>>
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>
>


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