Transistor Oscillator Simulation Convergence
NPN uses a default BF=100 parameter. Your circuit shows a collector resistor that is 100 times smaller than your base resistor, plus it must drive the next stage through a capacitor. These things suggest to me strongly that your collector resistor is too low in value (or that your base resistor should be lower.) If you don't change the default BF=100 value with the NPN model, then I'd recommend either increasing the collector resistor values or else reducing the base resistor values. Or, just increase \$\beta\$ by setting BF=200 or so.

The other aspect is charge storage within the BJT. The two parameters I'd want to change would be either TF or TR or both. TF is computed from the BJT's unity-gain bandwidth and TR is computed from the saturation time constant. In the NPN model, both these values are set to 0 which is not at all realistic and will cause problems in a circuit like this.

TF isn't actually constant in a real BJT, but the simpler models assume it is. (In reality, it varies with the collector current.) It is used to model the excess charge stored in the BJT when its emitter-base junction is forward biased and used in order to calculate the BJT's emitter diffusion capacitance. (You can work out the value using a power supply, small signal source, and an oscilloscope.) If you have no clue about its value, just use TF=300p. With RF BJTs, though, it will be smaller than that.

TR is more complicated to measure and models the excess charge stored in the BJT when its collector-base junction is forward-biased. It calculates the BJT's collector diffusion capacitance. If you have no clue about its value, just use TR=20n.



So, I'd probably just accept the NPN model but set things up like this:

.model MYNPN ako:NPN NPN(TR=20n TF=300p BF=200)


Or something similar. You might be able to get away with a lower BF. But given your resistor values, I'd avoid the temptation and stick with a higher value for BF than the default.