Two versions of the Eital-McCullough 4W20,000A power tetrode: at left., an early version (1952), cut open to reveal the “bombardment” cathode; at right, one from 1955. This tube is documented extensively in TC for oct. 2010. A very early bulbedd model, possibly the X486 protype, is illustrated on Norm Wilson’s n6jv.com web site.