[Milsurplus] Smart People: Gassy tubes , again

[J. Forster]

>     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