[kalee20]

Thanks Hugo!

Reading through with a bit more leisure, your vibrator-replacement using the two AZX17 transistors... I'm wondering why you didn't want the drive transformer to saturate?

If you let the main transformer saturate, the collector current shoots up at onset of saturation, and the fixed base current is no longer enough to keep the relevant ASZ17 in full conduction. So the collector voltage rises, the voltage across the main and feedback transformer falls, the base current falls, and the whole thing changes state. But, it is preceded by a rather stressful collector current spike.

If you design the feedback transformer so that this saturates FIRST, then at the onset of saturation the primary current in the feedback transformer starts to rise. But, it is limited by the primary resistance of 144 ohms, so you don't get a massive collector current spike. With more voltage dropped across the winding's resistance there is less available magnetically - the voltage across the feedback coil drops, the ASZ17 starts to turn off, and the circuit changes state as before, but much more kindly to the ASZ17's.

It's good to see, however, that the original power transformer gave operation at 60Hz-ish. Normally, operating frequency (around 100Hz) would be well-defined by the natural frequency of vibrating reed with a little mass on the unsupported end. So at 100Hz, the original transformer would be comfortably away from saturation.