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You used series diodes to protect the base-emitter junctions of the NPN. That's fine. But then you probably should include a galvanic connection across the diodes, as well.

In this case, something like this:

The resulting simulation looks like this:

Try out both and see how it works for you.

Just as a note, though. I used \$470\:\text{k}\Omega\$ resistors because I worried a little about the BJTs finding a quiescent point instead of oscillating. (I think your choice of \$150\:\text{k}\Omega\$ pushes too close towards allowing a quiescent point. The Sziklai pair has too much current gain.)

Just as a note, though. I used \$470\:\text{k}\Omega\$ resistors because I worried a little about the BJTs finding a quiescent point instead of oscillating. (I think your choice of \$150\:\text{k}\Omega\$ pushes too close towards allowing a quiescent point. The Sziklai pair has too much current gain.) I might go as low as \$330\:\text{k}\Omega\$. But no lower than that.

Just as a note, though. I used \$470\:\text{k}\Omega\$ resistors because I worried a little about the BJTs finding a quiescent point instead of oscillating. (I think your choice of \$150\:\text{k}\Omega\$ pushes too close towards allowing a quiescent point. The Sziklai pair has too much current gain.)