Aquiring parts for a 160 amplifier. Planning on (4) 813's with a tank circuit of 11 mh and 1000pf, but I've seen plate chokes from 47 ohms to 220 ohms and 2 turns up to 8 turns. I've also seen Amidon beads. Is there a formula for paracitics below 30 Mhz? Geo W7LFD