On Oct 1, 2005, at 6:36 AM, <exray@bellsouth.net> wrote:
> Wiil,
>
> For years it was and is common practice to outgas tubes by applying HV
> at low current i.e. one or two ma. till the tube arcs. Then reduce the
> HV a tad till the tube stops arcing. Leave the HV at this value for 30
> minutes or so. Then raise the HV slightly.
I have never heard this one. If this procedure works as advertised,
why do manufacturers build an ion pump into large electron tubes?
>
> Also try to run the tube at reduced HV and a heavy load. Get it as hot
> as possible.
Running a 3-500ZG as hot as possible will cause the carbon (graphite)
to outgas.
> Then reduce the current to 1 or 2 ma. and raise the HV. This is a long
> process. BE certain to use a current limited supply.
>
> When you can hold off 20 to 30% more than rated HV your finished!
The peak positive anode potential in a linear amplifier with a tank
circuit is about 2x the anode supply potential Healthy 3-500Zs are
rated at 4000V-max, yet they high-pot at > 15,000V -- or roughly double
what they encounter in linear service using a 4kV anode supply. If I
high-potted a 3-500Z that measured 4000v plus 30% -- or 5200v, I would
put it in the scrap bucket.
>
> George
> W4IW
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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