Hello dear community. I am new here as this is my first post ever.

I have decided to study on valve amplifiers and my first attempt is this G9. I am also planning on building it (of course!) but in lack of a budget (yet) and in excess of interest I am still trying to figure out the math and physics behind this (simple as it seems) design.

Now dear fellas, for my questions:

I am not 100% optimistic about my calculations but bear with me. Life's a journey of trial and error after all.

First of all, I have big trouble understanding the point of R7=47KΩ. I have calculated (for HT=245V) my V1 Bias Point at -6V for the 2.2k resistor. I also understand that the R7 resistor provides a voltage for the grid being a little lower than the cathode at all times. What is the purpose of this though? Studying valve theory I've seen the 1M Grid Leak and the 2.2k Cathode Bias shunting to the ground.

My second issue is about gain. I have calculated (my Bias Point is still 6V) my closed loop gain for the 1st Stage being Acl1=37 (that is for max input on the rotary, that is R11=1K). I have also calculated the 2nd stage gain being A=22.

I believe a microphone voltage output is about 15mV (right?) so I get about 100mV after the input trafo.

Considering my gain calculations, this all adds up to 77V for the 2nd stage output. That is about 35V on the output trafo, right?

I am fairly positive that I have mistakes in my math and understanding.

What's an ideal output (before output trafo) voltage on an audio preamp like this?

I've spent some time in the forum reading posts about this design and I have noticed that most people's troubles are about the PSU voltage regulation and such. I more concerned about the actual amplification circuitry.

I know I am not but an infant in a group of war veterans but, in my defense, valves are considered ancestral technology in my university (Electronics Engineering) and I also got s**t for brains