[Milsurplus] Smart People: Gassy tubes , again

[hwhall at compuserve.com]

The most interesting bit in that presentation is the note that old getters can be reflashed with some useful output. Seems like I have heard something like that before. I was curious about what sort of device could do the job.
  
If we have a tube that is gassy, is the reason (a) that the getter has lost its ability to capture the gas, (b) the gas is so tenuous it doesn't easily come into contact with the getter to be captured, or (c) the gas components aren't vulnerable to getter capture?
  
If (a), then reflashing a getter can improve the situation. If (b) or (c), it won't. But if (b), then the gas may eventually clean up via the getter, or may be inconsequential due to its small amount.
 

 Wayne

-----Original Message-----
From: Ralph Cameron <ramcam at magma.ca>
To: jfor <jfor at quikus.com>
Cc: hwhall <hwhall at compuserve.com>; milsurplus <milsurplus at mailman.qth.net>
Sent: Tue, Dec 3, 2013 6:54 pm
Subject: Re: [Milsurplus] Smart People: Gassy tubes , again

 
 
 
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 
> 
> 
> 
> 
 
--