>> 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
>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
- R. L. Measures, 805.386.3734, AG6K, www.vcnet.com/measures.
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