[Milsurplus] Smart People: Gassy tubes , again

[hwhall at compuserve.com]

 The surplus store has several of those in a bin. Next trip there, I'll see if any have instructions printed on them.

Wayne


-----Original Message-----
From: J. Forster <jfor at quikus.com>
To: hwhall <hwhall at compuserve.com>
Cc: ramcam <ramcam at magma.ca>; milsurplus <milsurplus at mailman.qth.net>
Sent: Tue, Dec 3, 2013 4:28 pm
Subject: Re: [Milsurplus] Smart People: Gassy tubes , again

 
 
 
I don't know much about CRT rejuvenators. It was discussecat length on the 
HP_Agilent list a while back. Their operation must be discussed in the 
literature, or maybe in the instruction manuals from maybe Sencor or B&K. 
 
-John 
 
===================== 
 
 
 
> I thought Ralph's reference to the 10 percent boost applied to tubes in 
> general. I did know that strongly heating a filament was reputed to drive 
> off accumulated contamination in some cases. But what that had to do with 
> helping the getter, I didn't 'get'. Or was the point perhaps that by 
> releasing it from the cathode the getter was able to 'get' at it & was 
> helped in that way. (Sorry for the puns, couldn't help myself.) 
> 
> One reads a lot of reports about how to rejuvenate tube cathodes, but the 
> ones that seem most credible are the ones that take the different cathode 
> chemistries into account. Though cathodes get poisoned by gas, perhaps I 
> ought not stray so far from the original issue of gas removal into a new 
> (yet old) cathode rejuvenation topic. 
> 
> 
>  Wayne 
> 
> 
> 
> -----Original Message----- 
> From: J. Forster <jfor at quikus.com> 
> To: hwhall <hwhall at compuserve.com> 
> Cc: ramcam <ramcam at magma.ca>; milsurplus 
> <milsurplus at mailman.qth.net> 
> Sent: Tue, Dec 3, 2013 3:12 pm 
> Subject: Re: [Milsurplus] Smart People: Gassy tubes , again 
> 
> >     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 
> 
> 
> 
> 
> 
> 
>