I did the sums using RB=20 and RE=100

OK with you so far - Rb/Re gives 0.2 which is less than the R.H.S - so is acceptable.

Then I decided that the other side of the equation always stays the same, so RB/RE has to greater than or equal to 0.2631ohms,

Again agreed (I used 230V rather than 240 and so got 0.27' but that's not significant)

so if RB is 20 ohms RE cannot be more than 5.26 ohms.

Now you've lost me - we started out with Re = 100 Ohms (with Rb = 20).


   - Andy.

I did the sums using RB=20 and RE=100

OK with you so far - Rb/Re gives 0.2 which is less than the R.H.S - so is acceptable.

Then I decided that the other side of the equation always stays the same, so RB/RE has to greater than or equal to 0.2631ohms,

Again agreed (I used 230V rather than 240 and so got 0.27' but that's not significant)

so if RB is 20 ohms RE cannot be more than 5.26 ohms.

Now you've lost me - we started out with Re = 100 Ohms (with Rb = 20).


   - Andy.