There is quite of bit of info if you start digging into 'West' amplifiers, Grand Funk and even searching Mel Schacher ... they used tubes that weren't nescessarily designed for those West amplifiers, and while it created the sought after distortion, it also tended to blow more than a few tubes along the way .. rumor has it they had a tech with nomex gloves on right behind the stack whose job the whole show was to replace the tubes in Mel's amp as he blew them (sounds good anyhow

) ... if I get time I will try and find the articles, they are somewhere in my files ...