I always like to study the schematics of the All American "farmhouse" battery radios. However I have never been able to lay my hand on an American vintage radio, even the 1940-50s amercian radio "tubes" are abundant in Europe. You called them" old junky radios", I call them treasures in the Uk
. I have been homebrewing the american classic farmhouse 4 tubes superhets both miniature and Octal base versions, now working on the homebrew of AC AA5 (without live chassis, rectifier and series filaments) and 12V B+ automotive AA5 from scratch.