For sale 2 tubes VT-231 (6sn7) Sylvania bad boys 

black plate

external welded 

silver foil getter botton 

black base 

clear glass 

military  specifications JAN CHS 

same code on glass F4

tested strong on tube tester TV7D/U 

test tube 1= 96 & 102 code on glass F4

test tube 2= 110 & 110 code on glass F4

reference good at 50 & 50 

reference 100% = 80 & 80 

top tubes strong performance , rare tubes 

box 196

pair 9