Recommendations on PTFE air tubing

I’m considering, slowly, an RCA cable design that’d utilize possibly PTFE air tubing possibly inside a larger PTFE tubing, so please recommend something, I’m sure air tubing is generally utilized in DIY work.
What would be good for encasing 24AWG wire, in terms of tube diamater and outer radius? Since PTFE is durable do you think a 0.1mm (0,00393") outer radius would be fine?
The amount of air I guess should be enough in terms of internal tubing air space that there’s at least the conductor’s radius’ worth of air between the conductor surface and the plastic? Fine, or is less fine for RCA voltage?
Since I need to balance the C and L by geometry, I don’t want the tubing creating too much distance between conductors, lessening the ability to manipulate their coupling as needed…

(Since talking of interaction between conductors, this would be a “pseduo-balanced” (as it’s called for some reason), design with signal and ground running as wire conductors inside a heavy enough passive shield.)

Have have you used with what, with good results?
I don’t want to spend too much on blindly testing results.

https://www.iconoclastcable.com/

Yes.
But I’m not designing a copy of the Iconoclast RCA, I’m of course trying to understand how to apply the concepts. Is the PTFE tubing dimension used in Iconoclast really universal enough to be scaled to any application? Etc.
(Why am I not copying the Iconoclast? I am, by principles that always hold, there’s just considerations with the geometry I have in mind whose properties are not addressed in Galen’s design briefs.

I’d use Hyperflex tubing:

So that’s 6.35mm diameter and yes, apparently superior to PTFE. That actually would be suitable for use as the larger outer air tube, over which I’d do the shields.
What I’m wondering, should I not have the conductors themselves in individual, smaller air tubing inside the larger tube, might be overkill? I’m getting molybdenum wire, so I’ll have to “insulate” it myself, maybe with just a suitable tape IF there’s no benefit from running that too through tubing. I’m guesing not.
(Is insulating bare wire by a tape (maybe a fabric one) any good?)

You could consider two layers of plumbers tape. Wrap one clockwise and the other counter clockwise.

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One layer might work. But I was thinking about bending and how that might open up a seam if just one layer.

Hi Arenith,

Have you seen these articles? I think the author is describing what you want:

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What is your goal? Thickness between the two wires matters can matter more than distance to a single wire. The whole field between the wire integrates through the dielectric.

Realistically, the total capacitance and dielectric absorption are so very low compared to the signal and source/load impedance not to be relevant. Intentionally having some L and C as tuning parameters will have more impact good or bad.

Well yes, that’s very close to what I had in mind actually! Are you clairvoyant or something?

Hi Arenith,

No - not a clairvoyant sadly.
I had only just read the 2nd article I posted a day or two before you asked your question so it was front of mind.

I’ve not made my own cables but I was sorely tempted after reading those articles.
I was impressed by the way the author explained the science behind the technical decisions.
And my understanding is he is happy to answer questions.

Good luck with your build!
Mark

I sent a question to him regarding some possible improvements.
The efficacy of the central conductor as a drain in an RCA configuration is under question, it surely has some effect but measuring the efficacy would require some more serious test gear… A possible improvement would be having a foil type conductor inside the tube for more surface area. Also given a foil width that’s close to the tube’s inner diameter would give a more consistent geometric reference, if that matters. Dunno.
The point of no screening and avoiding the added capacitance is very valid but then again I don’t want a totally unshielded RCA - conductive carbon tape might be valid here. My phono cables are shielded this way (with ground also as a wire along the signal inside) and they aren’t prone to noise, being phono cables, so apparently it’s effective. Won’t likely increase capacitance much, as metal screening would.