Andy,
I finished building and testing my OCXO today...
I started out trying a 15K resistor for R5 but found it limited the BS170 MOSFET's gate voltage too much. ?I could only get about 2.95 volts maximum on the gate with the temp adjustment potentiometer fully open. ?The MOSFET's took a long time to heat up like that. ?Next I tried a 27K resistor for R5 and found it to be just about perfect. ?Now the maximum gate voltage reaches about 3.35 with the potentiometer fully open.
I wound up having the potentiometer set to about 80% (just a rough guess) which results about 100 mW's of continuos heater current. ?Maximum startup current is about 225 mW. ?I can live with that.
73,
John
AA7US
AA7US