2d 21 The Sylvania Type 2D21 is a miniature four element thyratron with negative control character. 2D21. THYRATRON. OPERATIONAL RANGE. OF CRITICAL GRID VOLTAGE. TYPE 2D21 SHIELD
2d 22, 2D21. THYRATRON. OPERATIONAL RANGE. OF CRITICAL GRID VOLTAGE. TYPE 2D21 SHIELD.
