On the Cover

“Life tests on continous evacuation of 304TL / March 8, 1943” Shows impromptu test rig at Eimac’s Salt Lake City plant. Subject: 304TL triode is at upper center of photo, attached to a vacuum manifold atop an oil diffusion pump. An ion-guage tube is on the same manifold, to the left. A mechanical forepump is at lower left, supported by a wood packing crate. Tuned circuits to form a power oscillator are on a plywood plate at upper right, with three light bulbs a dummy load. Tube was running at 1600 v@ 600 mA, or 960 W input. Note the easy access to high voltage.

Photo: Perha_Eimac archive, a holding of History San Jose.