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Re: [Amps] Switching Power Supplies

To: amps@contesting.com
Subject: Re: [Amps] Switching Power Supplies
From: Tony King - W4ZT <amps080605@w4zt.com>
Date: Fri, 14 Jul 2006 14:56:43 -0400
List-post: <mailto:amps@contesting.com>
Tom W8JI wrote:
<snip>
>  I can't imagine why an amateur would want to use a 
> switching supply for a filament. What reason is there to do 
> that?
> 
> 73 Tom 

Tom,

The reason I chose a small switcher for my filament supply was to 
provide a stable DC filament voltage over changing input line voltages. 
The switcher I found was a fully shielded commercial variety that 
appears to be relatively RFI free, weighs less than the transformer 
normally used and generates none of the heat an analog regulator produces.

My experience with switchers may be limited compared to others but most 
of the problems I have seen have been noise coupled to and radiated by 
the incoming power line. The switcher for the amp filament has an output 
which is very clean on the scope over varying loads and input voltages. 
At the same time, there was very little detectable RFI from the line 
cord sniffing across the HF bands.

Well built switchers do exist but it certainly demands a proper 
application of that technology as you pointed out with the coupling in 
the ICOM and MFJ examples.

Thanks for your comments.

73, Tony W4ZT

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