Abstract: 1. An electron-discharge device comprising: an evacuated envelope; a cold electrode supported within said envelope; a thermionic filamentary cathode; and means including at least one spring member affixed to said cathode and supported from said envelope for normally supporting said cathode in tension in a position within said envelope spaced from said cold electrode and adapted to relax said tension in response to rapid acceleration of said envelope in a predetermined direction perpendicular to said filamentary cathode, the space between said normal position of said cathode and the inner wall of said envelope being substantially unobstructed in a direction opposite to said predetermined direction whereby said cathode is supported by said wall throughout substantially its entire length when subjected to said acceleration.