12ax7 ecc83 tube NOS Mullard Blackburn factory I61 B9J1 preamp tube test strong one piece
1 tube 12ax7 ecc83 Mullard NOS ,
Blackburn factory code I61 B9J1
tested on tube tester TV7D/U = 44 & 46 (reference good at 32 & 32)
grey ribbed plate , O getter
box 177