Wow, great responses guys, thanks
![Cheesy :D](https://www.eevblog.com/forum/Smileys/default/xcheesy.gif.pagespeed.ic.KPzuH4J-TG.png)
I have played with the R1 C1 values but, as has been predicted, the results can drift or be inconsistent.
Now I have several choices to look at:
1. Use a 74AUP1G86 XOR logic IC with Schmitt trigger inputs
1. Use a 74HC4046A PLL IC which will need a divide by 2 circuit for the feedback loop, probably just a JK flip flop
2. Use a tuned LC tank multiplier but won't that produce a sine wave output?
I'm discarding the transformer rectifier option as too expensive and large.
I will order components for all 3 and test each one.
Thanks again.