To: <amps@contesting.com>
>> Date: Fri, 22 May 1998 10:01:57 +0100
>> From: Peter Chadwick <Peter_Chadwick@mitel.com>
>> Subject: [AMPS] parasitics
>> To: 'amps' <amps@contesting.com>
>
>> I question the parasitic bending, because I don't see where the current
>> comes from. In an oscillation mode, as opposed to an arc, current is limited
>> by emission, and that's around 65mA per watt of heating current for a
>> thoriated tungsten filament. This gives an upper limit for the 3-500Z
>> filament assembly of around 4 to 5 amps.
>
>Actually the saturated emission current can be as high as 100 mA per
>watt at normal operating temperatures of 1900k (the section on
>Electron Emission, page 9-9, of Electronic Designers Handbook by
>Giacoletto).
>
>In pulse service, with 5.5 volts on the filament, Eimac supplied
>data indicates the saturated current is just over 10 amperes with
>3000 volts of positive grid voltage and 5000 volts on the anode.
>
>I think we can be very sure a typical amateur PA won't reach
>ten amperes.
>
Agreed, Mr. Rauch, however something is apparently capable of melting the
copper-wire in 1A rated chokes in the DC path of grid current, yet I do
not find evidence of arcs in the anode or in the grid. I should be
opening another filament-grid shorted today, and I will post the results
here -- provided they are not "unfriendly" to my agenda, of course.
>.......
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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