Paul Burridge wrote:
One thing bugs me about building oscillators and that's the
possibility that they may not start in the first place, or else start
fine then somewhere down the line just flip into an overtone or
sub-harmonic for no apparent reason.

Yes. This area is all about limit cycles, attracters, and such like, in
non-linear equations.

If only one could physically prod
the circuit around to induce instability but of course that's unlikely
to show up any potential problem. What's needed is some method of
instigating instability to try to show up any latent tendency for any
particular osc to go tits-up and I can only think of one practical way
of precipitating it: varying the power supply voltage.

There is no general solution to non-linear equations. One can only use
experience and brute force by trying the usual suspects.

If one can vary the supply over a fairly wide range and the oscillator
only responds by very small changes in output frequency and doesn't
jerk into another frequency/output mode altogether, is this a
sufficient test on its own of that oscillator's likely stability in
the field?

One tries varying components and the PS and hopes for the best:-)

Kevin Aylward

http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

"That which is mostly observed, is that which replicates the most"
http://www.anasoft.co.uk/replicators/index.html

"quotes with no meaning, are meaningless" - Kevin Aylward.