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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