2 x unused ECC86 tubes
Telefunken tubes with diamond <> on bottom
one tube still in its factory sealed box
Very good test result
S/gm = 5,8 + 5,5mA/V (100% = 4,6mA/V - usable starts with 2,8mA/V)
Final assessment: Only the slope/gm S/gm provides information about the emission
Further explanation: According to military standards, tubes with 60% (minimum value) were classified as usable.