My Si FF is a little lower than vcc/2, (0.2-0.3v). I trust my ears more than my DDM.

Marty, ever tried to set ib1 = ib2 ?

With Si the condition is, if ic2=vcc/2:

R2/R3 = vcc/2/vbe1*(1 - R4/R3/hfe2)

and

R1 = 2*hfe2*R2*(1 - vbe2/vcc)/(hfe1 + 1) - hfe2*R3/(hfe1 + 1)

R1=q1 collector resistor; R2=the sum of both q2 collector resistors; R3=the drive pot; vbe1=q1 base-emiter diode forward drop; R4=the feedback resistor; hfe2=q2 gain.

For example, if hfe1=90; hfe2=120; the drive pot R3=2k; R4=100k; vbe1,2=0.6v; vcc=9v then:

R2=8.75k; R1=18.9k; ib1=ib2=0.0042857ma; vc2=vcc/2.

Note that R4/R3/hfe2<1 or hfe2>R4/R3, that's why I used a drive pot of 2k.

With Ge leakage must be considered. Some more algebra.

Curious result I've posted long ago. I discovered this accidentally playing with R1 to find the best value.

mac