Hi Colin"So would they be the 30 pF ones Dorke mentioned above.?"
No.They are about 120p or higher. The mylar dielectric gave them the high capacitance.
On talkingelectronics.com under Crystal Set I show how to make a variable cap with cooking foil
Thank you very much. That's worth a fortune. I'm defintely going to try that. BTW have you seen the other sites with instructions for making air variable capacitors?
E.g.. http://www.eham.net/articles/5217
I'm tempted to try that, but I think I'm better off with yours first.
Thanks