I made many attempts at building a Colpitts oscillator, and this one by far supposed to be the most advanced and with high chance of success.
Yet, it's still not enough. I tested voltages on the amplifier and they all seem to be as I predicted in calculations, so the amplifier should be fine. I researched the air gap problem on cylinder rod cores and used this calculator to verify that this solenoid of around 300 turns, 0.1 mm wire, 10 mm diameter, 94 mm rod length, 100 initial permeability (for carbon steel) should have around 25 effective permeability and so inductance is from 5 to 7 mH, which should give around 9 to 11 kHz frequency. Yet all this huge effort that I put into this thing seems like a waste now.
Theory does not work in practice.
What could be the reason?