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[AMPS] 3-500Z

To: <>
Subject: [AMPS] 3-500Z
From: (2)
Date: Fri, 28 Sep 2001 21:26:05 -0700
>> Is the 500mA limit one imposed on safe conditions for the anode, or
>> for the cathode?
>Neither. It is a typical operating parameter based on a certain ratio 
>of peak to average current. 
>> 600mA @ 2600V = 1560Wdc input; output (measured) = 1100W; apparent
>> efficiency 70%, apparent Pd = 460W (realizing some drive power appears
>> in the output).  Under these condx the amp is just hitting a small
>> amount of compression (<1 dB) but with more drive the output will
>> continue to climb; problem is Ig, which gets hard to keep below 150mA
>> when you drive it too hard.
>As long as IMD is OK, you are OK. Unlike MOX cathode tubes, 
>thoriated tungsten tubes are NOT damaged by excessive peak 
>emission demands. 

//  Amen.

>They simply limit at a certain current. That is 
>why you can operate a thoriated tungsten filament at reduced 
>heating voltage with no damage, and why the tube can actually be 
>operated while the filament is still warming up without damage. 
>Now here is a neat thing to think about.
>Rich claims parasitics can somehow bend the filament from the 
>extreme currents making magnetic fields, many amperes! The 15 
>amperes of heating current won't bend it, but the plate current will.

//  AC current does not have the same magnetic effect as DC current.   In 
the autopsy photo on p.15 in the September, 1990 *QST* ("Parasitics 
Revisited"), the filament of a low-hours 3-500Z is bent enough to touch 
the grid-cage.  How would you explain this, Mr. Rauch? 
>He also claims the tube's emission will start to saturate at 400mA 
With a new 3-500z, saturation typically begins above 420mA avg., or 
1.25a-peak.  (p.7, Eimac 3-500Z Technical Data; 1-2-79)

>Which one is correct at what moment of time?
>Factually, the saturated emission current is just over ten amperes 
>in a 3-500Z...

//  Perhaps, however, I have seen #28 Cu wire melt and pi-wound grid 
chokes implode.


-  R. L. Measures, 805.386.3734, AG6K,  

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