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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