The amplification state of the triode is that the emitter junction is positively biased and the collector junction is reversely biased.

But in the first picture, only the signal voltage is applied to the emitter junction. Generally speaking, the signal voltage is too small to turn on the PN junction, so the emitter junction is not forward biased.

Secondly, after VBB is added to the emitter junction, the position of Rb makes the transistor unable to work normally due to short circuit at the input end when this pattern is static.

Therefore, a suitable resistor RB must be placed between the signal source and the base. In this way, an appropriate pipeline pressure drop can be obtained.

In chapter 2, the group member of the amplifier circuit is UBEQ >；; Uon and emitter junction are forward biased and collector junction is reverse biased.

Select the resistor correctly and match it with the power supply, so that the amplifier tube has suitable static working current.

The input signal acts on the input loop.

The output dynamic signal acts on the load.

This is the principle for judging such problems.

I hope I can help you.