Why on earth?

Differences in tubes over You-Tube?  Must be really really dramatic with linear and non linear distortions in double digits.  Well, some tubes are that bad so OK. 

Going NOS I assume? Ukraine sourced?  Russian or Czeck?

Love my tube amp but not a fan of YouTube for discovering new audio equipment.

So shoving rat poop in all the unused rca, xlr and speaker connectors isn’t going to make everything sound better?  And increase the soundstage?

Boy do I feel silly.😁

Maybe you forgot the foil triangles on all the door corners.  🤣

" Never understood that one"

It is in layman's terms "The psycology of advertising".

Billions of dollars in research has been done to learn what motivates consumers to want to buy a product.

Much of advertising is based on such research, which includes such factors as "association" (for example an attractive women in a car ad spreads her legs and says "Take me for a ride in your Lincoln".

Or simple repetition has also been proven to work very effectively to manipulate people's perception of a product and their need for it.  Just over and over repetition impresses the brain to believe and adopt what is being promoted.

Logical, rational thinking has almost nothing to do with effectiveness of advertising.