6h8c 6sn7 tube metal base preamp tubes matched pair black smooth plate oval mica on top badboy , pan getter , external welded 

2 tubes = pair 6h8c metal base tubes 

tested strong 112/120 ; 96/96 on tube tester TV7D/U military tube tester instrument calibrated ( good at 40/40) 

made in Russian federation in the 1950's 

box 120