Class B audio amp with auto bias

 While looking for the Knight kit KG-207 telephone amplifier documentation

https://wb9kzy.blogspot.com/2023/07/50-years-ago-was-50th-anniversary-of.html

I found the hardcopy of this EDN Design Idea:

https://www.edn.com/class-b-amplifier-has-automatic-bias/

I had tried this before but thought I'd reconsider it as far as a possible LM386 killer.  First I thought I'd try entering it into LTspice:

But I wasn't able to get it to accept the TI TLV271 spice file, LTspice is still largely a mystery to me :)

Then I thought just for expediency, try an LT1793 Linear Technology op amp in place of the TLV271:

This does simulate (after I also spec'd a value for C1) but I didn't take it too far since the currents involved were already way past the 2.7 mA idle current of the NJM386.

  Also using an opamp isn't right since this is supposed to be an all-discrete circuit.  One final problem is that the circuit (as configured) has no voltage amplification - it's really more of an impedance converter.

input in green, output in red

So three strikes means I've dumped it for now without retrying it on the breadboard.  But maybe I'll revisit it in the future since the automatic bias configuration sounds interesting.  

Best Regards,
Chuck, WB9KZY
http://wb9kzy.com/ham.htm