Hello Alan,

I recall you having some odd kind of J310 JFETs with Idss ~ 100mA and Up -3.6V or less. Is the same batch also used here for the VCO buffer stage?

I'm not sure what's up with those 100mA Idss JFETs (maybe rebadged PN4391?) either, but genuine J310s tend to have pretty uniform Idss round 40mA. That's also what I use. Philips (PMBF)J310 ones are an exception. Lower avg Idss and more variation.

you did a great work. why don't you try ratio detector as it works much better than yours one. you can use a Ratio detector coil. if you need any help to build Ratio detector coil let me know I can help you.