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Old April 2nd 21, 08:50 AM posted to
Big Bad Bob
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Posts: 366
Default rarity of LF and HF adjustable coils, coil forms, etc.

There seems to be a general LACK of non-N.O.S. and
non-ripped-out-of-gear RF coils for LF and HF band, ESPECIALLY the coil
forms needed to wind your own, particularly ADJUSTABLE ones.

If you're into antique radio restoration this could be a SERIOUS problem!

I _HAVE_ seen sources for ferrite [and most likely powdered iron as
well] core material as ferrite rods, though. There are also toroidal
ferrite beads of an appropriate length that would work.

So getting cor ematerial isn't the problem. It's the COIL FORM that is
the problem!

I think I have a solution involving a 3D printer, nylong screws and
nuts, and those ferrite rods of various dimensions.

Here's the basic plan: Using a ferrite or powdered iron core of a
reasonably correct size, construct a coil form around it that could work

* IF transformer inside of a can
* Peaking or resonant circuit inside or outside of a can
* ratio detector transformers

you'd use a 3D printer to make an appropriate coil form with the right
inside/outside diameter

You'd attach some kind of adjusting yoke, or make it part of the 3D print

You'd use nylon screw and nuts to make the adjustment stem

You'd glue a nut onto the core, and then attach [and glue] the nylong
screw to it

Now you have an adjustable inductor, one that may even fit in the
original can [if there is one], which you can wind yourself as necessary
using standard available coil wire.

This is all DO-able, and might solve the problem of HYPER-EXPENSIVE
N.O.S. parts and (generally) unavailable coil forms.

(aka 'Bombastic Bob' in case you wondered)

'Feeling with my fingers, and thinking with my brain' - me

'your story is so touching, but it sounds just like a lie'
"Straighten up and fly right"