Vacuum Tube Output Transformer Measurements Determining Turns & Impedance Ratio & Matching To Tubes

I have been asked a lot of questions over the years about transformers and this is my attempt to answer the basics - transformer/magnetics design is an engineering field all in its own so there are no YT videos that will make transformers a simple subject - I hope this helps the vacuum tube audio amplifier builder.
Here is another link that might help - http://www.ozvalveamps.org/optrans.htm