Power amp vs preamp topology

[john_guitar]

Greetings,

I have the following problem that I cannot fully understand.
In literature it is said that in a common preamp stage the topology for taking the output is as in attached figure top02.
However, when it comes to Power amplification they always put the output transformer in the place of Ra (plate resistor) like in attached figure top01. Is it possible to create a topology like the attached figure top02 (which is similar to a preamp stage).?

What are the differences between these two topologies??
They say that power amps must amplify also current (not only Voltage amplification). If do we amplify the voltage, the current is amplified also (according to the resistance), isn't it?

So, is it possible to have power amplification with topology in figure top01?

Thanks in advance

[Steve Conner]

Yes, some hi-fi designs use it, and they call it parafeed.

[Tom Phillips]

Your top 02 will produce little useful amplification.
Since you said that you want to "understand" this I am going to give you some homework reading which I think will answer your question plus many more that will probably follow.

Go to the page at Technical books online and download the Basic Audio series by Norman Crowhurst.

I believe that your current question will be answered by the Power Amplification section starting on page 2-67 of volume 2.

Have Fun,
Tom

[J M Fahey]

Top 01 produces *a lot* of power amplification.
As in producing, say, 10W with 1mW input (say, 15V RMS across a 220K grid resistor).
A Power amplification factor of 10/0.001=10000 (ten thousand).
It´s the typical single ended power amplifier.

Top 02 produces nothing because the transformer winding is shorting the DC supply to ground.
To boot, DC is fed through an impossibly high 100K resistor.

EDIT: Top 01 produces also Voltage amplification: about 200V RMS (at the plate) with about 15V RMS drive= about 15X voltage gain.
If you consider the voltage across the speaker connected to the secondary, you´ll have to divide that voltage gain by the output transformer turns ratio.