>G'day from Down Under,
> Our current project is a 3CX3000A7 GG
>amplifier. We have built the power supply and are now starting the main
>grunt department. The amp will be a monobander for 20m, with a possibility
>of changing tank coils to operate other bands but that may come later.
>
>The question is the filament choke. The filament runs 7.5V @ 50A and we
>were wondering how to wind a suitable choke. What we have in mind is to
>tape 3 or 5 ferrite rods (3/8" diam is all that is avail in Australia) and
>winding the HEAVY DUTY bifilar coil around the bundle so that we have a
>decent diameter to wind the thick wire onto.
Hi guys,
I don't know if bundling ferrite rods will work, but here is a suggestion
that I learned from some other people out here on the mail reflector:
If you wish you can just skip the chokes on the secondary of your
filament transformer and let it be at RF potential. Then you wind
smaller, low current chokes for the 120 or 240 Volt lines on the primary
of the transformer. The only thing you really care about is keeping the
RF out of your power supply.
If you do run the transformer at RF potential you MUST, MUST, MUST float
the transformer. DO NOT ground the case.
The advantage here is that you only have to wind small chokes for the 1.6
Amps or so at 240 Volts. That's a BIG difference.
Hope this helps.
73,
Jon
KE9NA
-------------------------------------
Jon Ogden
KE9NA
http://www.qsl.net/ke9na
"A life lived in fear is a life half lived."
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