[skyscraper]

I didn't use electrical tape, I used a strip of plastic cut from a resealable bag that components come it. I think they are made of polyethylene, which has a fairly low dielectric constant.

But the teflon sounds like a good idea, and is slightly better electrically than the other plastic. I have plenty around, too. Thanks!

The only problem with the coil now is the melted plastic introduced small gaps between some of the windings. That doesn't seem very significant to me, but I've ruled out everything else in the oscillator.