>Rich Measures said:
>
>>A correctly sized "glitch" resistor does not need to be replaced after
>an
>>"event". A HV fuse may not prevent gold-sputtering damage to the grid
>of
>>the tube from VHF parasites. {see photos in September 1990, QST}
>
>>Limiting peak current discharge current is quite probably more
>important,
>>and a fuse isn't fast enuff.
>
>Yes I think the fuse cannot be fast enough. However, I am begining to
>believe that the amount of damage sustained by an internal flashover
>(i.e. gold sputtering) can be lessened by the addition of a HV fuse.
If the fuse were helpful there would be no gold sputtering.
>Just for clarification, my reference to the word "flashover" is an
>electric arc
>thru free space from the high voltage DC line to a lower potential bus.
(to the grid collet, which is grounded)
>
>Internal, external, or whatever, due to gas,
If the tube is gassy - trash-time.
> parasitics, foreign
>particles or any other reason. I think repeated flashovers cause an
>accumulated damage that can eventually kill the tube.
A cathode-grid short caused by a cathode flake is fatal. However, a
moderate amount of loose gold melt-balls can be safely settled into the
base of the tube by tapping in the vertical plane.
>The lesser the amount of energy passed by each event, the better the going
gets in the
>long term.
>
True, Alex. Reducing VHF amplification is also useful.
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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