Math: What would need to change?

[fuzzy645]

For academic purposes, I'm wondering what would need to change in this circuit in response to using a much lower HFE rated NPN transistor.  The 2N5089 has a high HFE (I think in the 600 range), so what if it was swapped for a lower HFE NPN rated (lets say) along the along the lines of 200 HFE?

1. Would it be enough to simply tweak that 68K resistor by 9V battery + so that voltage into the emitter is approx 4.5V?

2.  Would any other components need to change (such as the series 220K resistors in the feedback section, as well as the 1K gain pot?

3.  Would a germanium NPN work?  I know there are often low HFE, so what about a Darlington Pair (although I have read that leakage will be an issue).

Thank you!!

[mac]

Negative feedback bias calculation with leakage:



I asumed that collector current is:
ic = hfe*ib + iL, hfe: current gain, ib: base current, iL: leakage

In this case R2 is infinite, so the thing gets very dependent on hfe, and temperature in the case of germs.

See my gallery, there is a small application I wrote to calculate bias of different biasing schems, including the FF.

mac