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Re: [TCML] Secondary form material



I don't understand your comment about PVC. As several others have pointed out already that PVC makes a perfectly dandy coil form if handled with reasonable care in selection and preparation. I've had excellent luck with something far older and simpler - cardboard tubes coated [and to some extent impregnated with] shellac. The cardboard is coated with thinned shellac on both the outside and the inside [takes a little doing] and the process repeated until the whole form is solid and quite rigid. The largest form I've made was for a "radio coil" and it was 7" in diameter. Measured RF losses were negligible and the coil has an excellent Q. My biggest TC secondary is wound on a 5-1/4" mailing tube treated the same way. I've used this approach because I had a good supply of thin-wall mailing tubes but if I were to build a coil now I'd probably go the PVC route, same as I do with VDG columns.

Ed

Andrew Robinson wrote:

As many have already discovered, PVC is apparently a terrible material to use as a secondary coil form. About a week ago my engineering group also discovered that acrylic is extremely hard to work with. We ended up cracking our only secondary coil form which we slaved over to find! So my question to everyone out there is what on earth should we use for the secondary coil form. We need a 4" OD coil form and if possible, if you can name a material that can also be an 1/8" thick we have a nice cutting tool that makes the most perfect end caps. So ideally 4" OD and 3.75" ID is perfect for what we need. I've called numerous plumbing companies with no help what so ever. Thanks everyone!

Regards,
Andrew Robinson



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