>>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.
>
Also, one needs to bypass the primary and secondary windings to the core
so that there is no RF potential between the windings. The transforner
can be mounted on a piece of 0.125" thick epoxy-glass [G10] board. The
core to gnd capacitance figures in the C2 tuned input values on the
higher bands. 20uH of L is plenty for 160m-10m coverage. More L is not
mo-betta.
>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.
Winding with #22 is a bit easier than winding with bar-stock.
>
>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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cheers
Rich...
R. L. Measures, 805-386-3734, AG6K
--
FAQ on WWW: http://www.contesting.com/ampfaq.html
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Search: http://www.contesting.com/km9p/search.htm
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