wrote:
>>
>> As many folks will remember from previous repetitions of this topic,
>> reasons for anode-screen arcs include:
>>
>> 1. Loss of load at a phase angle that results in extremely high anode
>> voltages.
>
>When load loss happens, the first thing to arc is the Tune-C.
Not in every amp.
>The resultant metal-vapour arc reduces the anode potential to a few
>tens of volts.
>
Correct.
>> With certain amps, you can make this happen anytime you wish:
>> remove load, apply full drive - BANG.
>
>The bang is not from an arc in a vacuum.
I never said it was.
>>
>> If the RF voltage is high enough, the anode flashes over to the next
>> lower-potential object within sight.
>> For a tetrode, this is usually the
>> screen, so the screen supply experiences a very large negative current
>> input from the tube.
>
>Flashover from the positive anode produces negative screen current? Now
>there's a new one.
Yes. Sit down and work it out.
>>
>> 3. Internal arcs due to gas release. I know that Rich doesn't like to
>> accept this;
>
>The reason is that I have autopsied a fair number of kaput electron
>tubes and I have yet to see any such arc craters or barnacles -- even
>in tubes that are gassy.
See the photos referenced in my other posting - which you have been
pointed to several times before.
There are many things that I haven't seen... but I respect the evidence
of generations of engineers who have made it their full-time business to
find these things out.
Bottom line: "Although good design measures can be taken to prevent
arcing, ionization and arcing WILL occur whenever high voltage exists."
(Eimac)
>The idea that a big-bang being heard is certain evidence of an arc in
>the vacuum of the tube's envelope is laughable.
Well, I never said it was.
--
73 from Ian G/GM3SEK
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