Material for coil bobbins?

[Geaney]

Hi Guys, what's the best material to use when making coil bobbins? I've found a source for brass eyelets and the tool to fit them. I was thinking of just using regular PVC pipe for bobbins but then that would probably get messy when soldering to the eyelets, etc. I guess cardboard with some shellac on it would work but I thought I'd ask the team before I go any further.

Cheers,

John

[AlanBeckett]

What sort of Bobbins John?
Mains? af?, rf? Iron Cored?

Alan

[pwdrive]

SRBP/Phenolic tube ?

Lawrence.

[camallison]

I have used these people in the past http://www.engineered-composites.co.uk/g...and-tubes/

Not sure what their prices are like as I had "purchase order access" to them and wasn't paying.

Colin

PS - email barbara@engineered-composites.co.uk as she may be able to supply from their offcuts bin.

[Yorkie]

To an extent it depends on the frequency the coil will operate at. Some plastics become lossy at higher frequencies - especially black plastics as they may have carbon in them. I read a useful tip some years back about testing coil formers for use at VHF/UHF. Put it in a microwave oven for a couple of minutes with a glass of water alongside to absorb some of the microwave energy. Remove the coil former and see it it's heated up much. If it hasn't then clearly its good at microwave frequencies so will pose no problems at lower frequencies.

I'd have thought that polycarbonate, acrylic, acetal, delrin, tunol, paxolin (or other phenolic resin) tubing would be fine. Trouble is that most suppliers seem to want to sell it in 2M lengths, but some will cut it down to your sizes. Though you don't mention any diameter John, if for example, if you wanted 20mm external/14mm internal, this outfit sell acrylic tube (as well as lots of other sizes, shapes colours etc) and would no doubt cut it into ten 200mm lengths for postage.

http://www.plastock.co.uk/Tube/Round/Acr...-p348.html 20mm OS 14mm ID £10.01GBP

(Don't know the shipping situation from UK to CH - if you do spot anything from UK suppliers who won't ship it to you, I'd be happy to get it and forward it on).

Hope that helps a bit.

[Nick]

I bought some thin paxolin sheet on eBay for not-a-lot - used it for the formers for my DAC90A o/p xfrmr...

eBay is good for that sort of stuff...

[Geaney]

Thanks chaps, I plan to make some rf coils for the (second) Radialva set I got for spares ages ago. I re-built the chassis mechanically but it needs re-wiring and the missing coils fabricated. One is about 3/8in dia the other more like 5/8in dia. Both bobbins are about 1in long.

I'll go hunting based on your suggestions.

Cheers, John

[pwdrive]

Are they slugged John, what frequency range?

Lawrence.

[Radio Fixer]

I have a 12" length of Paxolin tube that is 1/2" in diameter with a 1/16" wall (plenty thick enough). It might do both coils with a bit of experimentation.

You are welcome to some of that if it helps. Free !

Gary

[Geaney]

Thanks Gary, I've attached a photo from the original set I restored and you can see the two coils mounted on the right hand side of the chassis - the lower one is a single coil and the supper one has two coils on it. There are no slugs fortunately. I'm new to this coil winding stuff so I figured I start of with trying to reproduce the lower (single) one first and see how it goes. I'll PM my address and if you could spare about 3in of the paxolin tube that would be brilliant. I'm happy to pay postage of course.
Cheers, John