Sussed it in the end.
The problem was mainly too high a kv, the bb212 varicap has a high capacitance, just 1v correction voltage shifted the o/p a few khz, so the system was trying to make too small a change in voltage to track the frequency.
Lowering the gain a little by changing the bb212 with a pair of bb105's in parallel gets only around + and - 50 hz shift of the osc frequency for the entire 5v control range, the oscillator is now nice and stable.
I will need to replace the xtal with a 10ppm varsion, or use one of my crystal ovens.
Turns out my freq counter is off 65hz in 10m/c's, not bad seeing as all the house moves its suffered.
The problem was mainly too high a kv, the bb212 varicap has a high capacitance, just 1v correction voltage shifted the o/p a few khz, so the system was trying to make too small a change in voltage to track the frequency.
Lowering the gain a little by changing the bb212 with a pair of bb105's in parallel gets only around + and - 50 hz shift of the osc frequency for the entire 5v control range, the oscillator is now nice and stable.
I will need to replace the xtal with a 10ppm varsion, or use one of my crystal ovens.
Turns out my freq counter is off 65hz in 10m/c's, not bad seeing as all the house moves its suffered.