[AMPS] Network analysis of suppressors

[measures]

>
>Hi Ian,
>
>> Tom, please explain in your view, why tube type amplifiers are fitted with
>> suppressors. And when amps with 3-500z's (for example) go band, why do
>> they go bang?
>> 
>> Ian, ZS6BTE
>
>Tubes flash over because something either exceeds the normal 
>breakdown voltage, or because something inside the tube lowers 
>the breakdown voltage.

Ian asked about a bang.  External arcs can make a loud bang.  In a 
vacuum, arcs do not bang.  
>
>It's pretty common for 3-500Z's to gas up a little and flash over. The 
>gas comes either from internal material outgassing or seal leakage.
>
>The arc itself can getter the tube, and remove the gas. As a matter 
>of fact controlled arcs can be used to getter certain tubes in 
>manufacturing. 
>
>The 3-500Z normally getters itself when the anode reaches 
>temperatures that show some color. In order to completely getter, 
>some 3-500 anode designs have to be heated to a red color.

Heating a graphite-snode 3-500Z/8008 to a red color apparently increases 
the amount of  leakage current in the tube.  
>
>There is nothing sinister about an arc. 

Especially an arc which leaves no mark.  
>
>What amazes me is how people conclude a tube will arc from 
>some momentary parasitic that occurs one every year, 


Owners of amplifiers who report arcs, often report they heard a big bang. 
   An arc inside the tube can not make this sound. As far as I know, Tom 
Rauch is the principal person who concluded that the tube itself arced.  

> but the very 
>same tube WON'T arc from 8 kV of peak RF voltage at the signal 
>frequency. 
>
>What is particularly amazing is the anode impedance and Q of the 
>circuit is many times lower at VHF than at the operating frequency, 
>and yet some people actually seem to believe more voltage is 
>developed at VHF than at the fundamental frequency!

If the Tune-C had no resonances, this would be quite true.  In the real 
world, Tune-Cs have resonances.  What is the first resonance of the 
Tune-C in the AL-80, Tom?
thanks
>
>This whole parasitic thing is pretty odd, from a technical standpoint.
>
A large amen to that.  If you have not read it, and you are intersted, I 
can snailmail you a copy of G. W. Fyler's article on parasitic 
oscillation in the 1935 Journal of the Institute of Radio Engineers.  
>
cheers, Tom

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