I just wanted to be useful with my list of free books...If he is serious... I dont know that but i am trustful of people ...

No one here will explain him in few line the function of this power tubes...

I advise him to ask for atmasphere help politely; he is one of the best tube amp and class D  designer and he is here very often in audiogon ...

Common guys, give him a break. You do not have to know how a technology works to realize it does.

I’ve asked this question directly to humans and haven’t had good answers. I don’t think many people really do know. Google reference is not good on this point for some reason. YouTube doesnt offer an explanation of what happens inside a tube that I could find without getting odd vids scarily technical and not helpful.

And then there’s this amazing forum which offers incredibly smart people willing to offer their knowledge and be very helpful.

So this is my last hope

The book is free...

http://www.guitarstudio.tv/documents/Designing-V-T-Amplifiers.pdf

This one is free too...

http://www.introni.it/pdf/18%20-%20Vacuum%20Tube%20Amplifiers.pdf

This book is free too :

https://pearl-hifi.com/06_Lit_Archive/15_Mfrs_Publications/GEC_UK/GEC-UK_AF_Amplifier_Design.pdf

more basic and free book :

http://www.tubebooks.org/file_downloads/bereskin_buildit.pdf

Very good book here , begin here :

https://www.vtadiy.com/book/

Deeper book :

https://www.theseus.fi/bitstream/handle/10024/126712/Popovs_Sergejs.pdf?sequence=1&isAllowed=y

Another one :

http://www.lundahl.se/wp-content/uploads/datasheets/amplifier_30wpp.pdf

I will stop here...

And listen to this short youtube video :

Let's design an build a vacuum tube amplifier from scratch

https://www.youtube.com/watch?v=9AABLml-ERE

This OP  is a bit provocative , between a bot and a narrow mind audiophile... He never ask a question by curiosity and sincerity it seems... He already know the answer and laugh in his beard ...

I may be wrong... But it is what i think after his thread about S.S. and tubes amp.