Guys see that resistor there where I have the red pen. Should that be there in this model?

I'm trying to think - maybe it's some type of double source transformation or something.
I'm thinking that Vi is across that hie + whatever else is to the right of it.

So what's with the VT and the RT? Why go to the trouble?

 

Vt and Rt are simply the Thevenin equivaent of the signal source driving the transistor. This way the effect of a non-ideal source can be dealt with. If Rt is not there then the driving source would be an ideal voltage source (zero impedance).

 

Yeh I was thinking that myself Electrician. He's setting us up for other types of models then. KK it just wrecked my brain last night. Thanks for the confirmation

 

Recently another person asked how to bias the same transistor circuit you show. So I simulated it to show its severe distortion without any negative feedback and the very low distortion (and low gain) with negative feedback: