[ARC5] [Boatanchors] More and More "Gassy" Tubes

[J. Forster]

You need some Ip, IMO. If there is no electron flow, the gettering process
does not work properly.

It takes an electron flux to ionize the neutral gas atoms. W/o the
electrons, no ions.

Neutral atoms are not attracted to anything.

-John

====================



> Residual gas from sitting on a shelf is very common, even with tubes of
> relatively recent manufacture.  For example, when I replaced a set of
> 6146B
> finals that were purchased fresh in 1980 and installed in 2005, I
> neglected
> to give them a little "burn-in" before firing the rig back up for the
> neutralization.  My impatience was punished with a couple of
> inter-electrode arc's at first.  Then I just stopped and left the tube
> with
> heater and HV applied (no Ip because it was easy to run it this way) for a
> few hours.  Although the tube wasn't very hot, it was sufficient to
> activate the getter and clean up the residual gas.  After that little
> exercise the tubes performed flawlessly.
>
> Dennis AE6C
>
>
> On Mon, Apr 21, 2014 at 8:53 AM, Bill Cromwell <wrcromwell at gmail.com>
> wrote:
>
>> On 04/21/2014 09:58 AM, J. Forster wrote:
>>
>>> Tubes are not perfectly sealed, and some gasses (He especially)
>>> diffuses
>>> through glass. That's the bad news.
>>>
>>> The good news is many can be saved. That's what the getter is for. BUT,
>>> the tube MUST be operating for the getter to work. The trick is to
>>> power
>>> the tube without destroying it and let the getter to do it's job.
>>>
>>> Apply normal filament.
>>>
>>> Apply negative grid bias to ensure cutoff through a roughly 100k
>>> resistor
>>>
>>> Apply about 150 to 200 VDC to the plate through a current limiting
>>> resistor to limit current to roughly 1/2 max Ip.
>>>
>>> Slowly reduce grid bias, until Ip is about 20% of design Ip.
>>>
>>> WAIT. At least a day.
>>>
>>> The above an all be done on a tube tester.
>>>
>>> Retest for gas.
>>>
>>> -John
>>>
>>> ===================
>>>
>>>  I have done this and had about 95 per cent success. Obviously if the
>> glass is visibly cracked or the getter looks like chalk or cobwebs it
>> isn't
>> going to work.
>>
>> 73,
>>
>> Bill  KU8H
>>
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