Tansistor models

For the two problems in the attachment.I have been trying to calculate Vbe but the value I'm getting is always > 0.7V, which is wrong.

Feedback Amplifier Analysis

The solution is included. Only further explanations are required. I don't understand how the 2-port parameters in part 3 work. For the gain in part 4, what is the theory for dividing it by Ro + the top. If you could just go over it that would be great! Parts 5,6,7 make sense. Simple, easy to follow explanations please :)

Differential Amp Analysis

Finding resistance for differential stages

Multi-Stage Amplifier

Questions about a two stage amplifier

Worked out problems request

I am trying to get more practice working Basic BJT Amplifer problems for my Electronics class. However, I don't know if I am doing the problems correctly. Please give me (at least) 3 worked out problems with explict explanations of every step from the DC KVL equations, the Hybrid pi values, the small signal equivalent circuit, and how to find the voltage or current gains. I need some lucid examples to clear up why my when I work the problems they don't come out right (as compared to the answers in the back of the book). Please address a moderatley involved common-emitter amplifier, emitter-follower amplifer, and common-base amplifer circuits. I don't really understand how to ass... click for more