[Amps] toroid filament choke?
Will Matney
craxd1 at ezwv.com
Wed Oct 27 01:41:14 EDT 2004
Tony,
You have to keep in mind the current surge there until the heater warms
up. The colder the heater is, the more current it draws. I would use a
conductor with at least 750 cir mils per ampere. For 3 amperes, that
equals out to be about 16 AWG wire for the minimum. Without doing any
calculations, a higher inductance is indeed needed for 160 meters. The
core referred to would only be about 2-1/4" ID core which is probably
about the smallest one could use. I was thinking of more like a 2-1/2"
ID. The core can be wound two different ways. One way, bifilar and the
other with two windings on each 1/2 of the core. I prefer the bifilar
for this. Once you determine the core you want, you need to figure the
circumference of one turn of wire. Then figure how many turns the core
will hold. Multiply the two and add the lead lengths. Cut two pieces of
formvar insulated magnet wire this length and wind the choke. One could
use a TFE insulated wire but you cant get as many turns this way because
the insulation is thicker. The number of turns needs to fill the core
until a space at the bottom between the start and stop is about 30
degrees from the center of the Toroid. A few turns here or there wont
matter much. Last, you want to check the self resonance too. There's
generally texts on how to do this in dip meter manuals. If yours don't,
check out the old Heathkit dip meter manuals.
Tony King wrote:
> Thanks Will,
>
> I was thinking they should be fine and your comments about keeping
them close to the tube are right in line with what I was thinking. I
had another response, off list as well, which suggested that I needed a
hole circumference which was 7 inches to insure I could get enough wire
inside for 160 meters but I think it can be much smaller with only a 3
amp filament requirement.
>
> I know you're one of the resident experts on transformers so I bet
you have a good opinion on that one ;)
>
> 73, Tony W4ZT
>
>
> At 12:18 AM 10/27/2004, you wrote:
>
>> Tony,
>>
>> Ferrite toroidal heater chokes work just fine as far as I've seen.
You would think that coupling to other components could happen but this
is not the case. Ferrite toroids have a self-shielding property to where
the flux wont hardly couple to anything around it. Thats the reason why
you have to add a winding to check one with a dip meter. Iron toroids
are another thing and will directly couple. However, it's best to mount
both these out in the open on the chassis by themselves, and the use of
bypassing is a must as in any choke. Typically, they're mounted as close
to the tube socket as possible and tie directly to the heater pins.
>>
>> Will Matney
>>
>> Tony King wrote:
>>
>>> Do any of you have opinions about using a toroid in a filament
choke for a GS-35B G-G amp covering 160-10 meters? I am thinking that it
would be much more practical than any rod type choke since the single
tube filament current requirements are only 3 amps.
>>>
>>> Core size and types, core sources, inductance and stray resonances
are things that come to my mind. I'm sure there are others. All of
your opinions and suggestions are invited and welcome.
>>>
>>> 73, Tony W4ZT
>>>
>>> I can't spell ;)
>>>
>>>
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