Guillermo,
It's impossible for the getter to absorb gas unless the anode is heated up hot
enough to do it, if that's where the getter is at. I read some have two
filaments of zirconium made to heat up to two different temperatures. The high
heat one to absorb, O2, CO2, etc, and the lower heated one to absorb the
hydrogen the hotter one emitted. If it's tantalum, you don't have to heat it up
as hot, nor have two different temperatures. The temperature on it though runs
around 1000 deg C (red-orange hot) for optimum absorption. If it is the anode
type, the anode has to be heated red orange for tantalum, and yellow to white
hot for zirconium just to absorb the gas properly. Under 300 deg C which is
just under where you can't see the anode turn red in the dark, is where
zirconium will not do any good at all, neither for hydrogen or O2 and the
others. These heat colors work for any metal, but not for graphite. You can
check them against any heat treatment or metalurgical chart.
In running the heater only, if the heater isn't coated in something to absorb
gas which it shouldn't be, can liberate a slight amount of gas into the tube
where it gets as hot as it is. The only way to get the anode up to the correct
temperature then for an anode type getter would be to apply anode voltage so
the anode will heat up.
Best,
Will
*********** REPLY SEPARATOR ***********
On 7/29/06 at 12:49 AM GGLL wrote:
>Ian White GM3SEK escribió:
>
>>
>> It also explains why transmitting tubes generally need to be pre-heated
>> after a long period out of use. The process of slow diffusion to the
>> surface of the materials means that gas will probably have accumulated,
>> and the getter needs some time at a high temperature in order to do its
>> job.
>
> Very clear explanation, Ian, thank you very much. I want to ask
> something
>about.
> This pre-heating process (in, for example, NOS tubes or those used in
>good
>condition but long time stored ones) must also be done by making the anode
>orange hot in high power tubes (those with "gettered" anodes) or it's just
>enough to run them with filament on for many hours?.
>
>
>Best regards
>Guillermo - LU8EYW.
>
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