MY GUESS IS YOUR TUBE WAS GOING FLAT. THERE ARE A LOT OF RF RATED MICAS ( WW II ERA SURPLUS) OUT THERE.. IF YOU WANNA CONJECTURE.. BUT HAVENT SEEN THIS DESCRIBED PROBLEM IN THE GLOBE KINGS I HAVE HAD OR WORKED ON. BECAUSE OF THE CONSTRUCTION OF THOSE DOOR KNOB CAPS ( ESSENTIALLY PRESS FIT TOGETHER) MOISTURE CAN DEGRADE THEM OVER TIME. LARRY W6WUH