Ok, many of you have suggested rather than just simulation I should actually
build something. Joe (W3JDR) has kindly donated a circuit diagram which I
started off with.

Best way to get going quickly is dead bug style, soldered straight to the
copper side of a PCB. I have never used this style of construction as it
looked flimsy, but it looked like a good way to go just for prototyping.
Well, the circuit went together fast and the finished product is very
steady, so I am now a convert to this construction method! I may need a new
iron though, as the basic low power model I have struggled to heat up the
large area of board.

Firstly I built the circuit (almost) as directed, slight modifications were
made to suit parts I had. Fixed capacitors were used as this allowed
evaluation without worrying about the diodes performance. The oscillation
voltage across the tank was about 1 vp-p measured with an older 50MHz CRO
and a 1:1 probe. Oscillation seemed stable and I liked the result.

Question: I used the ARRL equation for a cylindrical inductor and seemed way
off (50%). Should I expect the copper sheet to affect the inductance, and
how.

I then replaced the fixed capacitors with BB909 (3-30pF) diodes. The result
wasn't so good. Oscillation voltage was less (lower Q tank maybe) and the
stablility seemed poor (again poor Q). I will attempt more measurements
tonight.

James.