[Amps] tube flatulence - gettering

[R.Measures]

On Nov 19, 2004, at 12:15 PM, jsb at digistar.com wrote:

> On Fri, 19 Nov 2004, R. Measures wrote:
>
>> Hello, Jason -- Blue on the glass is not gas.  It is caused by
>> high-speed electrons fluorescencing the fluxing agents in the glass
>> recipe.  If the blue light is in the region between the anode and the
>> grounded grid, that's atmospheric oxygen and nitrogen getting through 
>> a
>> bad seal.  Normally, glass fluorescence occurs in areas where the
>> electron stream from the hot filament misses the anode and hits the
>> glass.  In time, the struck area of the glass turns brownish.
>
> Interesting - so is it safe to assume that the blue fluorescence does 
> not
> appear when idle because the tube has no bias to pull the electrons 
> away
> from the ionization cloud?

Correct, Jason

> The blue glow only appears when the amplifier
> is keyed and its intensity does not change when producing RF output vs.
> ZSAC.
>
> I'm bludgeoning the explanation but hopefully you'll get the gist - hi
>
>> Amperex 8163s have a solid, machined graphite anode-cooler that has no
>> gaps where the filament-glow can be seen from above.
>
> I would love to see that machining process...
>
>> OTOH, Eimac 8163s have a sheet-metal anode cooler with small gaps
>> between the fins that allows one to see the filament-glow.
>
> Nothing to be seen in any of these tubes inside the anode "compartment"
> between the interior of the anode and exterior of the grid cage.  The 
> blue
> glow is most noticeable, obviously, when the room lights are off but 
> only
> along the interior of the top dome of the glass envelope, and only when
> keyed.


>
>> My guess is that these sight-paths to the filament is where the glass 
>> is
>> fluorescing.
>
> That's it exactly.  There also are "spots" along the base of the grid
> flashing (or whatever it is called) that coincide with the openings 
> along
> the base of the anode flashing.  Brownish smudges inside the glass as
> well.  The 3-400Z you hi-pot tested at 2000V, "rode hard, put away 
> wet",
> is the one that's the worst.

This means it's emitting the most electrons -- which is hardly a bad 
thing.  However, a tube that has only 2000v of BD is almost certain to 
eventually grid-filament short.
>
>> -- I have not seen any gettering take place in any gassy 8163/3-400Z 
>> or
>> 3-500Z.  Neither Amperex or Eimac mentions such on their tech. spec
>> sheets.
>
> I wish I could find specs on the Amperex 8163 - I have searched high 
> and
> low on the net but no results.  I guess i'm looking in the wrong place.
>
I have a copy somewhere.  There is nothing extraordinary on it.

cheerz,

Richard L. Measures, AG6K, 805.386.3734.  www.somis.org