>Rich Measures wrote:
>>>I disagree. A microamp hipot tester will not be capable of any plasma
>>>generation..if you want to try and duplicate the fault conditions.
>>>
>>My highpot tester has plenty of current capability to create a gas plasma
>>in gassy tubes. The bluish plasma glows plainly in a darkened room.
>
>But that's only a high-voltage, low-current glow discharge. The highpot
>tester cannot create a low-voltage, high-current arc. Only the B+ supply
>has the muscle to do that.
>
A high-pot. is not being used to possibly bend filament helices. It is
being used to measure gas leakage at 9kV in fil.-grid shorted tubes that
*already have bent filament helices*.. The issue at hand is whether or
not filament-grid shorted tubes have gas.
>As far as I can see, the damage mechanism has to involve an arc powered
>by the energy stored in the B+ supply.
Why are there no arc-marks in tubes I have autopsied that have a
filament-grid short?
>We can be sure that the filament
>doesn't have the emission capability to supply enough electrons for the
>current involved, and the space charge in the vacuum doesn't store
>enough electrons or enough energy.
I am not so sure because I have seen too many 1A grid/gnd RFCs whose
copper wire has melted in two. We pretty much know what the repetitive
peak emission capability is. However, in a one-shot event, who really
knows?.
>
>An arc can start from an extremely small release of gas. It then feeds
>itself from ions ripped off the metal surface, but after a short time
>these will 'plate out' on the inside of the tube.
>
>There should be some visual evidence of surface erosion caused by an
>arc,
I agree that there should be a permanent arc mark in the metal at the
points where the arc struck.
>.......
cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
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