Good point kubeek.
Yes I did find that unlike the jfet that can only go negative the dmos fet can go a couple of hundred mv positive and still be operating in its linear region, not a brilliant thing for a battery application as Id will be at its max.
Jims circuits in the referenced page all have a bias resistor in the drain and even an Led!, and the unused gate is biased too, the vlf receivers preamp is a bit of a bodge.
Interesting Jim also couldnt get a grounded fet preamp to work either.
Another improvement I can make is to put a few pf mimmick cap inline with the Bfo, the o/p is 3 or 4 volts and blasts the rear end.
Thanks guys.