• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Using mains transformer as output transformer

It’s an ALL TUBE PA rig.
OK. I don't see the point in it, and I'm glad I won't be the one physically loading it in/out. I used to do FOH with a bass player with an Ampeg SVT 300W tube head which he used because "tone". Thing must have weighed 40kg, where my SS head was 6 and no one would have been able to tell the difference between his mine, especially with the right 200g pedal in front of mine.

Good luck with your project, but it seems to me like trying to build an RC plane out of concrete as an engineering challenge.