[Amps] Outgassing tubes.

[Will Matney]

Bill,

Your correct. That's a similar thing to what is done in cleaning or rejuvenating a CRT. The arc burns this stuff off and restores it's function. I've saved a many a CRT using a rejuvenator. Any sharp point will arc quicker than a dull point. But, if you start to get arcs on a regular basis, chances are you have a gassy tube.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 10/2/05 at 9:10 PM Bill Fuqua wrote:

>At 08:10 PM 10/2/2005 -0400, Will Matney wrote:
>>Jim,
>>
>>I should have added that those arcs, even though one might think minor, 
>>put's a quick surge to any power supply of several amps current similar
>to 
>>taking the B+ lead and quickly shorting it to ground and back off. This 
>>over time can weaken components like rectfiers and filters until one
>fails.
>>
>>Best,
>>
>>Will
>
>
>I have been on vacation and just got back and saw this thread starting 
>with"Question".
>     OK, you apply HV to a tube and it arcs a couple of times and then it 
>is OK. Does that mean that you have remove gas from it or gettered the gas 
>somehow? No!  You may have conditioned the tube. There is a procedure 
>called conditioning. This is often done in vacuum devices that have high 
>voltage applied to their internal elements, not just vacuum tubes.  You 
>start at a lower voltage and raise it until you get an arc. The current is 
>limited so that you don't cause serious damage to the elements.  The arc 
>discharge removes sharp pieces on the elements blast away tiny pieces of 
>stuff on the elements that produce field ionization at lower  voltages.
>You 
>continue this until you get to the operating voltage on the elements that 
>you desire.  I believe there is an EIMAC application note referring to
>this 
>in some of the higher power tubes.  Sometimes little bits of stuff in the 
>tube get where it should not  be or sharp edges are formed during the 
>manufacturing of the tube.
>     I have just gotten back from quite a long drive and ready to call it
>a 
>night. I have not read all the email on this subject so if I have repeated 
>something someone else has said I apologize.
>
>73
>Bill wa4lav
>
>
>
>
>>*********** REPLY SEPARATOR  ***********
>>
>>On 10/2/05 at 1:31 PM Jim Reid wrote:
>>
>> >Will wrote,  in part:
>> >
>> >> Plus with age, a small amount of atmosphere can seep in,
>> >> especially on glass tubes and where the ceramic to steel
>> >> meets on a steel tube. Though on any old tube that finally
>> >> does start to do this more, one should think about replacing
>> >> them sooner or later. They could end up damaging the power
>> >> supply.
>> >
>> >Perhaps that is what happened to my little AL-811H.
>> >My tubes were "only" about 10 or 11 years old, however.
>> >They were used very little over that time;  maybe they gassed
>> >up slowly from the atmosphere.  Would that account for
>> >the low transconductance shown,  see below?
>> >
>> >I sent the
>> >tubes over to KH6CDO in Honolulu.  He measured three of them
>> >at 800 umoh. Spec is supposed to be 900,  I think he said.  The
>> >fourth tube could not be tested.  The "glued-on" anode connector
>> >atop that bottle had come "unstuck" when I removed the plate
>> >cap connector.  Frank tried to file off some of the glue residue
>> >to get it conductive from the anode for the test;  he couldn't remove
>> >any of it;  I wonder if that tube ever participated in the amp,  hi.
>> >Or,  maybe it was the tube which arced?
>> >
>> >Anyway,  as Will suggests above,  it was the power supply
>> >where failure is now found.  Will see what it is in a few
>> >days or so.
>> >
>> >73,  Jim W6KPI
>>
>>
>>
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