Conrad Tube
DC Amplifier Triode
~1924

This tube was designed and patented by Frank Conrad, Westinghouse engineer. As shown in the cut-away, the tube used four parallel connected filaments, each with its own grid. A WD-11 type base was used. Conrad claimed this structure gave four times the Gm of an ordinary tube without a corresponding increase in grid-plate capacity. The patent application was made in 1924, but as far as is known the tube was never produced commercially.