Bifilar choke windings vs tube length ratio

[Hillio]

I posted the same question at OUPower, but would like to hear you guys' take on it also.

Has anyone figured out the optimal number of turns for the bifilar chokes for a given SS tube length? I keep reading everywhere that the number of turns depends on the tube length, but I have yet to see a suggested ratio. I'm working on a cell right that has 7 tubes which are 11 inches in length.
Also, how important is the special ferrite core material to cell operation. I would like to use some 1/2" rusty steel rod I have to make the chokes if it would not create problems. I assume that efficiency would not be as good with steel cores, but if they will still work OK for testing purposes I would like to use them.

[HeairBear]

Just an idea... Find the weight of one tube and match that in weight of the wire. Equal mass?  So, if your tube weighs a pound, the amount of chosen size wire should weigh a pound also. Or, you can match the mass of the secondary of a step up transformer. If your secondary has 600 turns of a chosen size wire, the chokes would also be wound 600 turns of a chosen size of wire. It may be possible the tubes are cut to match the circuit.

[malcolm]

yes, i believe nobody has yet to come up with a ratio.  the no. of turns depends on the length and dia of the core and the target inductance.  in order to achieve resonance both the impedance of the bif and the caps must be equal.

you didn't mention the OD,ID and the gaps of your cell.  the gaps plays an important role in gas prod and cap value.

there are links on this threads regarding cap calculations (sorry, but i can remember where they are at the moment... these guys have massive amounts of info in thread and even i am overwhelmed...  not to mention the great efforts that they do... whew!!!)   knowing the cap value and your target freq, you can now calc your chokes.

there is big difference between iron and ferrite cores... permeability plays a role here..using ferrite greatly decreases the no. of turns required of a particular indc value.

i know i'm not much of a help here...being a newbie myself.... i myself needed that ratio to minimize awg wire going to waste.
goodluck on work.

[Hillio]

Thanks for the replies.  Any ideas or suggestions offered are helpful for sure.
My tubes are 3/4 inches OD for the inside tube and 1 inch OD for the outside tube.  I need to check the gaps with a feeler gauge, but I'm pretty sure that it's 2mm or less.  I'll have to dig around and try to find that info about calculating capacitance based on tube size and spacing.  It's also good to know that using a ferrite core will require less turns to get the same impedance as opposed to an iron core.

Thanks again

[Farlander]

You have to use the ferromagnetic metal to get a good and strong EMF.  Wouldn't trust a rusty tube.  I don't think the exact same length or mass of the choke is the answer.  It would be fairly impossible to achieve (like tuning tubes).  Perhaps a variable choke can be utilized... perhaps even one that is varied by the cell itself...  that would achieve resonance automatically.