Filament Choke

[Duppy Conquerer]

Hello Fellas,
My project calls for a filament choke capable of handling 75 amps of cathode current at the lower spectrum of 27 MHz for a mono bander. I have seen a broad band choke that has the capability that i am looking for, however, the physical dimensions makes it problematic, in that, i only have 1/2" in to spare after the choke is installed without taking into account isolation from chassis...the choke in question measures 3 1/2" in diameter and the under chassis cavity is only 4" from top of the underbelly of chassis to bottom of enclosure, which basically leaves me a little less than an 1/2" of wiggle room. Now, here are my concerns:
Magnetic fields coupling to chassis ground potential creating all sorts sonic introduction to the input of the cathode circuitry.
Question here now is, the feasibility of the madness...will i be able to squeeze by?

 

[Duppy Conquerer]

No response to the dilemma

Ok, it's been quite some time since i requested some feedback with reference to the dilemma i have been having, and i have decided to construct my own filament choke. I am now invoking the knowledge from big boys lurking in the wings..come on now. Again, this is for a mono bander on the lower side of 27 MHz spectrum. I will need a good reference material, size of the required magnetic wire, and size of the ferrite rod.
Looking forward to hear from you guys.
73
Duppy Conquerer

 

[Captain Kilowatt]

I can't imagine a filament choke 3 1/2 inches in diameter. As for wire size consult a copper wire table for the proper size to carry the required amps. 75 amps would require at least 6 gauge wire with 4 gauge being better. Enameled magnet wire is preferred as it can be wound in a tighter circle because of the lack of bulky insulation. You do not need a lot of inductance at 27 MHz especially if you install bypass capacitors on the cold ends of the choke between the choke and the transformer.As for the size of the ferrite core, well that would depend on the inner diameter of the choke. Basically stuff it full of ferrite rods.

Now I have a question. No offense intended but if you are having this kind of dilemma over a simple filament choke are you sure you can tackle the meat and potatoes of the rest of the project? Filament chokes are dead simple whereas high voltage and RF currents in tank circuits etc can be far from it.

 

[KM3F]

75 amp heater current sounds like a pretty big tube is contemplated for a lot of power on CB band.
You better know what your doing.

 

[Duppy Conquerer]

Thanks for the quick response, and the information. Ok, the part that i am trying to get an handle on is the permability and size of core to use, bearing in mind that i have limited real estate under chassis - 4 inches in depth. Also, i realize that the choke needs to be shielded from strays, so i want to give plenty of head room. As to your question or concern, no offense taken, as a matter of fact, it humored me somewhat, but was well taken. I do have the confidence for the undertaking, and do understand the dangers involved. Do you have any suggestive reading materials on the subject?
Thanks much.
Duppy Conquerer

 

[Duppy Conquerer]

KM3F
I seek for knowledge..and my thirst has been quenched. Thanks.