[Milsurplus] "Blue Glow" mystery.

[J. Forster]

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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