[Milsurplus] Smart People: Gassy tubes , again

[Ralph Cameron]

John/Wayne
The attached link sheds a little light on getters in general but not on 
rejuvenators.
http://tubecrafter.com/tubecrafter_015.htm

Ralph
VE3BBM
On 12/3/2013 6:05 PM, J. Forster wrote:
>>      I remember those, but as I remember them, the rejuvenators were
>> installed and left in place for the remaining life of the picture
>> tube. It's easy to see how the higher temperature can comepensate for
>> a cathode's waning emission ability.
> Yes.
>
>> I don't understand how running the filament at boosted voltage for only
>> 20 mins affects the getter function. Is it because the getter flash
>> material gets hotter? If so, would longer times also make a greater
>> difference for tubes with more gas?
> No. A picture tube has a large surface area. The amount of gas that
> diffuses in is proportional to surface area, all other things being equal.
>
> Now, when a gas atom is struck by an electron, it acquires a (+)positive
> charge, so it flees the plate and moves toward the cathode. When it
> impacts the cathode, it 'poison's' the cathode. An increased voltage for a
> short time, 'boils' off this poisoning to some extent, cleaning the
> cathode and improving emission.
>
> This is why I suggested running a tube at 10% to 20% of rated current. If
> you degas at higher Ip, the cathode gets poisoned and Gm goes down.
>
> BTW, I -think- that the TV rejuvenators are used with the electron gun
> biased off, but am not cert6ain.
>
> FWIW,
>
> -JOhn
>
> =================.
>
>
>
>>     Wayne
>> WB4OGM
>>
>>
>>
>>   -----Original Message-----
>>   From: Ralph Cameron <ramcam at magma.ca>
>>   To: milsurplus <milsurplus at mailman.qth.net>
>>   Sent: Tue, Dec 3, 2013 9:18 am
>>   Subject: [Milsurplus] Smart People: Gassy tubes , again
>>
>>
>>
>>
>>   One may remember the trick of restoring CRTs that had lost emission due
>>   to filament contamination. Some of the so called "CRT" rejuvenators
>>   boosted the filament voltage with directly heated cathodes to burn off
>>   some of the accumulated "junk" in the vacuum. Most of this junk was
>>   metal contaminants. A 10% boost in filament voltage for 15-20 mins may
>>   help the getter.
>>
>>   Ralph
>>   VE3BBM
>
>
>
>

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