http://techchannel.att.com/play-video.cfm/2011/12/19/AT&T-Archives-Modern-Aladdins-Lamp Here is, albeit 'old', film describing ''vacuum tube theory''. Even you other ''old-timers'' will enjoy and you 'newbies' get a glimpse of the grand-days of electronics, telephone and radio broadcasting.... 73 Marv k2vhw