The Balun Designs bifilar-wound choke-baluns use #16 or #14 (not sure) bare wire slid into very small Teflon tubing. (I think Amidon has it).
I use the 1171, rated at 5kw and 10kv - - with T-network and ladder line.
Good pictures, graphs, and specs on that site.
73, --kv5r
PS: no connection to them, just a customer.
