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Re: [Amps] Ferrite Rod

To: "Larry Carman" <lncarman@swbell.net>, <amps@contesting.com>
Subject: Re: [Amps] Ferrite Rod
From: "Tom W8JI" <w8ji@w8ji.com>
Date: Wed, 3 Jan 2007 08:14:52 -0500
List-post: <mailto:amps@contesting.com>
Parallel bifilar wound chokes are fine, as long as each 
winding goes to an opposing filament terminal. Of course you 
would effectively lose half of the choke impedance with two 
chokes in parallel, a 100uH choke would become the 
equivalent of having just 50uH.

>   I believe you'll be safe running paralleled 30 amp 
> chokes in front of the
> 800 CFM. If you don't have the chokes already wound you 
> might wind single
> windings on each ferrite rod leaving just a very small 
> space between each
> winding for air flow across the rod itself.

 We *never* want to do this with high current filaments. The 
reason being nothing cancels magnetizing flux caused by the 
many ampere turns of the single winding and the core often 
saturates. The result is at best a loss of RF choke 
impedance at the filament, at worse it will introduce hum as 
the filament current modulates the reactance causing large 
reactance swings at a 120Hz rate (two impedance nulls and 
two peaks per AC cycle).

73 Tom 


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