Ok so I have looked at prob. 200 different old black market amp designs, home brew Ham designs and all of Heathkits, Dentron, and Alpha's popular models. I have been trying to cherry pick those feature I like in the various designs. Because I can read Russian and German I have been looking at their designs too. Although I will say my technical Russian is not even close to my German. Do not waste you time trying Googles Translation matrix it butcher's the Russian to the point that it is often gibberish. So Swan and Kenwood both had models marketed to Amateurs that used 6lq6 tubes or tubes in that family ie magnoval 9 pin with cathode cap. Everyone thinks no legit amp designed for Amateurs used cheap sweep tubes but at least these two companies made models with them.