[Amps] Tetrodes

[Ian White GM3SEK]

  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