>
>Rich Measures wrote:
>>
>>>
>>>It has always appeared to me that normal well documented arcs
>>>and sparks in tubes have been used to sell nichrome.
>>>
>>Tom -- My position has always been that unless gas is subsequently found
>>with a high-pot., an arc is not logical. Tom's answer is that the gas
>>disappeared because of gettering. Is gettering very likely while the
>>tube is being removed from the amplifier for high-pot. testing?
>>
>Yes. If there is a small gas release, the gettering action (which
>depends on the gas molecules colliding with the metal surfaces) would
>take place on a timescale of seconds.
A big bang is heard. The main breakers blow. What souce powers the tube
during the gettering? It is my opinion that instant gettering is
undiluted codswallop.
> That's way too slow to prevent an
>arc, but fast enough to clean up the vacuum before you can get the tube
>to a hi-pot tester.
>
>>
>>>Terry's amplifier very well could have been the victim of just such a
>>>common effect, but since it is not nearly as well publicized outside
>>>engineering circles as parasites it is overlooked.
>>>
>>Barnacles that disappear?
>>'
>Microscopic 'whiskers' may be a better term. They can start an arc by
>field emission, but are burnt off by the high current density.
With copper atoms, yes. I have never heard of tantalum atoms forming
whiskers. When copper whiskers arc and burn away, a slight tink sound is
heard.
>
>
>However, I'm still uneasy about Terry's experience, because that seemed
>to be reproducible on demand, which is not characteristic of a random
>event like an arc.
The 2K-4 has some fairly unique resonances. The anode-resonance is
c.95MHz. The 29uH HV RFC has a resonance near 95Mhz. The output
compartment appears to have a resonance near the same frequency. My
guess is that the resonance freq. of the output compartment can be
slightly tuned by lifting the lid. . When a 2K-4 has a parasite,
several turns of the HV RFC are typically toasted
>
cheers, Ian
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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