Tuning range of this beauty? - UK Vintage Radio Repair and Restoration Discussion Forum

Al (astral highway) · 24th May 2017, 6:13 pm

This is a pull from probably a Racal board.
I would like to use it to fine tune my magnetic loop antenna (in parallel with a small hand-wound inductor)

It appears to have a fine brass mechanism to vary inductance, but by how much? I'm guessing a fraction of a uH??

I have several, they're not easy to extract from a double sided board with integral ground-plane!!

Thanks folks

Restoration73 · 24th May 2017, 6:38 pm

Are you sure this is not a trimmer capacitor? A small variable inductor will have a coil
construction - small values have a plastic former with an aluminium slug.

Al (astral highway) · 24th May 2017, 7:03 pm

It's so tiny that it could be either. If it's an inductor, it has stray capacitance. If it's a capacitor, it has stray inductance!

TonyDuell · 24th May 2017, 7:11 pm

Of course. Every component has resistance, capacitance and inductance. Actually I can believe in zero resistance (superconductivity), but not zero capacitance or inductance (which would require major changes to electrodynamics).

But what is the DC resistance between the connections of this component? A trimmer capacitor would be open-circuit, a (small) inductor essentially short-circuit.

jimmc101 · 24th May 2017, 9:11 pm

Looks very much like a glass piston trimmer capacitor to me.
First hit on Google gives these. None are identical to yours but some appear to be quite similar.

Jim

Al (astral highway) · 24th May 2017, 10:23 pm

Quote:

Originally Posted by jimmc101

Looks very much like a glass piston trimmer capacitor to me.

Cheers, Jim! I love that company! Been a while since I ordered from them but they always have things that are unobtainium in th UK!

24th May 2017, 6:13 pm	#1
Al (astral highway) Dekatron Join Date: Nov 2006 Location: London, UK. Posts: 3,496	Tuning range of this beauty? This is a pull from probably a Racal board. I would like to use it to fine tune my magnetic loop antenna (in parallel with a small hand-wound inductor) It appears to have a fine brass mechanism to vary inductance, but by how much? I'm guessing a fraction of a uH?? I have several, they're not easy to extract from a double sided board with integral ground-plane!! Thanks folks Attached Thumbnails __________________ Al Last edited by Al (astral highway); 24th May 2017 at 6:14 pm. Reason: Forgot photo

24th May 2017, 6:38 pm	#2
Restoration73 Nonode Join Date: Jun 2013 Location: Surbiton, SW London, UK. Posts: 2,801	Re: Tuning range of this beauty? Are you sure this is not a trimmer capacitor? A small variable inductor will have a coil construction - small values have a plastic former with an aluminium slug.

24th May 2017, 7:03 pm	#3
Al (astral highway) Dekatron Join Date: Nov 2006 Location: London, UK. Posts: 3,496	Re: Tuning range of this beauty? It's so tiny that it could be either. If it's an inductor, it has stray capacitance. If it's a capacitor, it has stray inductance! __________________ Al

24th May 2017, 7:11 pm	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,208	Re: Tuning range of this beauty? Of course. Every component has resistance, capacitance and inductance. Actually I can believe in zero resistance (superconductivity), but not zero capacitance or inductance (which would require major changes to electrodynamics). But what is the DC resistance between the connections of this component? A trimmer capacitor would be open-circuit, a (small) inductor essentially short-circuit.

24th May 2017, 9:11 pm	#5
jimmc101 Heptode Join Date: Mar 2009 Location: Portsmouth, Hampshire, UK. Posts: 674	Re: Tuning range of this beauty? Looks very much like a glass piston trimmer capacitor to me. First hit on Google gives these. None are identical to yours but some appear to be quite similar. Jim