Geo. C Clark Detector
DC Detector Triode
~1922

This is a very interesting type of solonoid tube. The filament is a small tungsten loop that sits inside the plane of the nickel hoop that serves as the plate. The grid is the spiral winding just outside the plate and has one end tied to the normal grid pin and the other end tied to the shell. The bulb is etched Geo. C Clark, and Clark is stamped into the top of the plate hoop. For more information see the George C. Clark write-up in the articles section.