Only used , not abused, domestically, ie not bumped around ina van at any time. Mechanically broken dome end of GT badged Sovtek 5881, neat circular crack. Black deposit around a jet out of the envelope matching a black deposit on the metal "protection" cage screwed to the cab back panel. Gripper function around valve base was fine. Not obviously valve/cage touching, but close, I will reposition this cage 1/4 inch lower down. Is this a recognised design/construction failing perhaps Russian 5881 a bit longer than 6L6.
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on