Re: [Amps] toroid filament choke?

[Will Matney <craxd1@ezwv.com>]

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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