[AMPS] parasitics

Rich Measures measures@vc.net
Fri, 22 May 98 07:37:04 -0800

>> 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 
>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. 


R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures  

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