bft66 spice
Phase noise and frequency accuracy are two different issues. You are referring to an oven controlled oscillator, the SC cut has higher Q, less temperature dependence . I don't do oven controlled oscillators I am just interested in the basic noise theory and improvements but I am not in the business of making these, this is pure research ..
For these oscillators you MUST have a coarse mechanical tuning and a less then 1 Hz electronic tuning
Below 30 MHz I would use 2N4416 and above a modern bipolar transistor with Ft of about 5 Ghz, and Ic max of 60 to 100 mA.
In the DC circuit, the PNP transistor samples the DC current up to some offset, and within the loop gain and bandwidth compensates this. The third transistor act as a temperature stabilizing diode. It inverts the voltage drop at the output, including the noise by -180 deg and feeds it back so canceling these contributions to some high degree
Ulrich